Glossary
Every technical term used across the curriculum, with a plain definition. Terms gain entries here as pieces are authored.
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__resolveReference A per-entity resolver function required by the Apollo Federation subgraph spec. When the router… _entities A root-level Query field added to every Apollo Federation subgraph schema. The router sends a li… 'use client' directive A React directive placed at the top of a module file to declare that the file and everything it… /authorize endpoint The authorization server URL (RFC 6749 §3.1) where the client redirects the resource owner's bro… /token endpoint The OAuth 2.0 server endpoint (defined in RFC 6749) where a client exchanges an authorization gr… 0-RTT A QUIC and TLS 1.3 mode where a returning client sends encrypted application data in its very fi… 1-RTT The standard QUIC handshake for a new connection: the client sends its TLS 1.3 ClientHello and Q…A
abstract data type (ADT) A specification that describes what operations are supported and what they do, without specifyin… access token A short-lived credential, defined in OAuth 2.0 (RFC 6749), that a client presents to a resource… accumulator A variable initialized before a loop that collects or combines values from each iteration—sum, p… ACK A TCP segment flag and field that confirms received data. The acknowledgment number tells the se… adaptive sort A sorting algorithm that detects and exploits existing order in its input, running faster when t… adder (circuit) A digital circuit that adds binary numbers. A half-adder takes two single-bit inputs and produce… adjacency list A graph representation using an array (or map) of lists, where each vertex stores a list of its… adjacency matrix A graph representation using a V×V matrix where cell [u][v] = 1 (or weight) if edge (u,v) exists… advisory lock An application-defined PostgreSQL lock (pg_advisory_lock) not tied to any row or table — commonl… algorithm A finite, unambiguous sequence of instructions that transforms given inputs into desired outputs… alias bomb A DNS attack in which an attacker crafts a chain of CNAME (alias) records that forces recursive… aliasing (variables) The situation where two or more variable names are bound to the same object in memory — both hol… ALPN A TLS extension (RFC 7301) where the client lists its supported application protocols in the Cli… Amdahl's law Amdahl's law states that the maximum speedup of a program using multiple processors is bounded b… amortized time The average time per operation, computed over a sequence of operations. Some operations are expe… anagram Two strings are anagrams if they contain the same characters with the same frequencies. Example:… anycast A routing scheme where the same IP address is announced by multiple servers in different locatio… Apollo Federation An open specification for composing multiple independently deployed GraphQL services (subgraphs)… AppendEntries The Raft RPC that a leader sends to followers both to replicate log entries and as a periodic he… APQ (Automatic Persisted Queries) An Apollo GraphQL protocol where the client sends only a SHA-256 hash of the query string instea… argument A value supplied by the caller at the call site, e.g. add(3, 5) — 3 and 5 are arguments. Argumen… ARP Address Resolution Protocol: maps a known IPv4 address to a MAC address within a local network s… array A data structure that stores elements of the same type in a contiguous block of memory, allowing… array index An element's position in an array, counted from 0. The index is converted to a memory address by… ASCII American Standard Code for Information Interchange. A 7-bit character encoding that maps integer… assembler A program that translates assembly language source code into machine code, one mnemonic at a tim… assembly language A low-level programming language that uses human-readable mnemonics (like ADD, MOV, JMP) as a th… assignment The operation that writes a new value into the memory cell bound to a variable. In TypeScript/Ja… asymptotic Describing how a function behaves as its argument grows toward infinity, ignoring constant facto… async Short for asynchronous. The approach where a program sends a request to a slow device and, inste… at-least-once A message-delivery guarantee that ensures every message is delivered to the consumer at least on… at-most-once A message-delivery guarantee where a message is sent once and never retried, so it is delivered… aud claim The aud claim in a JWT (RFC 7519) identifies the intended recipients of the token — typically a… authoritative An authoritative DNS server holds the definitive zone records for a domain and answers queries d… authorization code A short-lived, single-use code returned by the authorization server to the client's redirect URI… auto_explain.sample_rate The fraction of statements the auto_explain extension logs plans for — used to capture slow-quer… autovacuum PostgreSQL's background daemon that automatically runs VACUUM and ANALYZE on tables, reclaiming… auxiliary space The extra memory used by an algorithm beyond the input itself: new arrays, temporary variables,…B
backend_xmin The oldest transaction ID that a PostgreSQL backend's current snapshot still considers potential… backhaul The aggregation link between edge access points — cell towers, Wi-Fi base stations, remote offic… backtracking A recursive technique that explores all candidate solutions by building them incrementally: choo… bandwidth-delay product The product of a link's bandwidth and the round-trip time (RTT), measured in bytes: BDP = bandwi… base address The byte address of an array's first cell — the fixed anchor the array name refers to. Every ele… base case The condition in a recursive function that stops recursion and returns a result directly, withou… baseline profile An Android performance artifact that lists classes and methods to be compiled Ahead-of-Time by t… basic operation The single representative step counted when analysing an algorithm's cost — for example, the com… batchLoadFn The user-supplied function passed to DataLoader's constructor that receives an array of keys acc… bearer token An access credential defined in RFC 6750 where possession alone grants access — no cryptographic… BGP Border Gateway Protocol: the path-vector routing protocol that exchanges reachability between au… Big-O notation A mathematical notation that expresses an upper bound on how an algorithm's time or space grows… binary Relating to a system with exactly two states or symbols (0 and 1). Computer hardware uses binary… binary search A search algorithm that operates on a sorted array by repeatedly comparing the target with the m… binding (variable) The association between a variable name and the memory address of the cell that holds its value.… binomial coefficient The mathematical expression C(n, k) = n! / (k!(n-k)!), read as 'n choose k', which counts the nu… bit The smallest unit of data in a computer: a single binary digit that can hold exactly two values,… bit pattern A specific sequence of 0s and 1s occupying a contiguous set of bits in memory. A bit pattern by… bloat The wasted disk space that accumulates in a PostgreSQL table or index when MVCC dead tuples are… blocking call A call that does not return until its work is finished. When the work is a slow device, the call… boolean A value that can only be true (1) or false (0) — a single bit interpreted as a truth value. Name… boolean (JS) The JavaScript primitive type with exactly two values: true and false. Represents a single binar… branch misprediction A branch misprediction occurs when the CPU's branch predictor guesses the wrong path, forcing th… branch prediction Branch prediction is a CPU mechanism that guesses the outcome of a conditional branch before it… branching factor In a recursion tree, the number of recursive calls made by a single function invocation. For exa… bubble sort A comparison-based sorting algorithm that repeatedly passes through the array, swapping adjacent… bucket A container (list or slot) in a hash map or hash table where items are stored after hashing. Mul… bytecode A compact, platform-neutral intermediate binary representation produced by compiling source code… Byzantine fault tolerance A class of failure in which a node behaves arbitrarily — sending conflicting, incorrect, or mali…C
cable Broadband internet delivered over the coaxial (HFC) infrastructure originally built for cable TV… cache hit A request that the cache satisfies from a stored copy without contacting the origin. The hit rat… cache key The identifier a cache uses to look up a stored response — typically composed of the request URL… cache line The fixed-size unit of data transferred between main memory and a CPU cache — commonly 64 bytes… cache locality The degree to which a program's memory accesses cluster in space and time, determining how effec… cache miss A request the cache cannot satisfy because the data is absent, expired, or invalidated, forcing… cache stampede A failure pattern where a popular cache entry expires and many concurrent requests simultaneousl… Cache-Control An HTTP response (and request) header that directs caches how long and under what conditions a r… call stack The memory area where function calls store their local variables and return addresses. Each recu… callback A function handed to a non-blocking call with the instruction to run it when the result is ready… candidate In Raft consensus, a candidate is a server that has timed out waiting for heartbeats from the cu… candidate solution A potential complete solution being built during backtracking. Initially partial, it may or may… CAP theorem A fundamental theorem in distributed systems proving that a system can guarantee at most two out… CDN Content Delivery Network: a geographically distributed set of edge servers that cache and serve… certificate An X.509 data structure that binds a public key to an identity (domain, organization, or person)… chaining (separate chaining) A collision resolution technique where each bucket stores a linked list of key–value pairs. When… character A single letter, digit, punctuation mark, or space in a string. Each character has a code (e.g.,… character code The numeric value representing a character, typically ASCII (0–127) or Unicode (0–1,114,111). Us… choose-explore-undo The core pattern of backtracking: (1) choose a value or branch, (2) recurse (explore) deeper wit… cipher suite A named combination of algorithms — key exchange, authentication, bulk encryption, and MAC — tha… circuit (logic) A network of logic gates connected so that the output of one gate feeds the input of another. A… circuit breaker A resilience pattern that wraps calls to an external dependency and tracks failure rate. When fa… circular buffer A fixed-size array treated as a ring: two pointers (front and rear) wrap around using modulo, el… client_credentials grant An OAuth 2.0 grant type (RFC 6749 §4.4) where a confidential client authenticates directly with… client_secret A shared secret issued by the authorization server to a confidential client at registration, use… clog_buffers How many CLOG pages PostgreSQL caches in shared memory; too few causes disk I/O during visibilit… co-location Placing services or components that communicate frequently on the same host, rack, or data-centr… code_challenge The value sent to the authorization endpoint in a PKCE flow (RFC 7636): a Base64URL-encoded SHA-… code_verifier A high-entropy random string (43-128 characters, RFC 7636) generated by the client at the start… coding gain The reduction in the required signal-to-noise ratio (in dB) that an error-correcting or data-com… collision A hash collision occurs when two distinct keys produce the same hash value and therefore map to… combination A selection of k items from a set of n items where order does not matter. {A, B} and {B, A} are… commit index In the Raft consensus algorithm, the highest log entry index the leader knows to be safely repli… commit log (CLOG) PostgreSQL's transaction-status log (pg_xact/): two bits per transaction id recording committed… compiler A program that reads source code in a high-level language and translates the whole program into… complement In two-sum, the complement of a number x (given target t) is t - x. If x + complement = target,… complete binary tree A binary tree where all levels are completely filled except possibly the last, which is filled f… complexity scoring A GraphQL server-side technique that assigns a numeric cost to each field in a query's AST befor… composite In browser rendering, a composite layer is a portion of a page that the browser promotes to its… compositor layer A separate GPU-backed surface the browser promotes for an element when it needs to be composited… compositor thread A dedicated browser thread that composites rasterized layers into the final frame and handles in… concatenation Joining two or more sequences — strings, arrays, or byte buffers — end-to-end to form a single s… concurrency Dealing with many tasks by interleaving them on a single core: the tasks take turns and only one… congestion control TCP's mechanism for preventing network collapse by adjusting how much data is in flight. It star… congestion window A sender-side TCP variable (cwnd) that caps the number of unacknowledged bytes allowed in flight… connected graph An undirected graph where a path exists between every pair of vertices. A directed graph with th… connection migration A QUIC feature that allows an existing connection to survive a change in the client's IP address… connection storm A connection storm is a failure mode where a large number of clients simultaneously attempt to e… consensus A distributed-systems problem in which a cluster of nodes must agree on a single value despite n… consent screen The UI screen shown by the authorization server where the resource owner explicitly approves the… const declaration A variable declaration using the `const` keyword that seals the binding — the variable cannot be… constant time An operation that takes O(1) time regardless of input size — the number of steps is bounded by a… constraint A rule or condition that restricts the valid values or states in a system. In databases, constra… consumer group A named set of Kafka consumers that jointly consume a topic, with each partition assigned to exa… consumer rebalancing In Kafka, the process by which the group coordinator reassigns topic partitions across the activ… contiguous memory Contiguous memory is a block of memory addresses where elements are stored consecutively with no… continuous profiling The practice of collecting CPU, memory, and other profiling data from production services contin… core One complete fetch–decode–execute engine inside a processor. A core executes exactly one instruc… correctness A property of an algorithm or program that guarantees it produces the right output for every val… crash The controlled termination of a program by the runtime when an exception is raised and no handle… crash-fault-tolerant (CFT) A property of a distributed system that lets it continue operating correctly when some nodes cra… CRLite A Mozilla scheme that compresses the full set of WebPKI certificate revocations into a compact f… CSSOM CSS Object Model: a browser API that represents parsed stylesheets and computed styles as JavaSc… cum-time (cumulative) In sampling profilers such as pprof and Python's cProfile, the cumulative time attributed to a f… cursor-based pagination A pagination strategy that uses an opaque cursor — typically the last row's ID or a composite so… cycle A path that starts and ends at the same vertex, traversing at least one edge, without repeating…D
datagram A self-contained, independently routed packet that carries enough addressing information to be d… DataLoader A utility library (originally by Facebook) that coalesces individual .load(key) calls made durin… dead-letter queue (DLQ) A secondary queue in a messaging system that receives messages the primary queue could not deliv… deadlock A cycle in the lock-wait graph where each transaction holds a resource another is waiting for, s… Debezium An open-source platform of Kafka Connect source connectors that implements log-based change data… debugging The disciplined process of locating the cause of incorrect program behaviour. Because the machin… declaration (variable) The statement that reserves a memory cell and establishes the name-to-address binding for a vari… decorrelated jitter A retry-backoff strategy in which each wait interval is chosen uniformly at random between a bas… degree The number of edges incident to a vertex. In a directed graph, in-degree is edges pointing to th… delivery semantics The contract a messaging system makes about how many times a consumer receives each message. The… deoptimization (deopt) The process where V8 discards optimized machine code for a function and falls back to executing… depth limit A GraphQL server guard that inspects the query AST before execution and rejects any query whose… deque Double-ended queue: a data structure where insertion and deletion occur at both ends (front and… dequeue To remove and return the element at the front of a queue. In a FIFO queue, dequeue removes the o… deterministic A property of a process whose output is fully determined by its input and starting state: given… device code flow An OAuth 2.0 grant type (RFC 8628) for input-constrained devices such as smart TVs. The device d… digit One of the ten symbols 0-9 that numbers are written with. directed graph A graph where edges have a direction: an edge (u,v) points from u to v. Also called a digraph. C… divide and conquer An algorithm design paradigm that recursively splits a problem into smaller subproblems of the s… DLQ (dead-letter queue) Abbreviation for dead-letter queue. In practice, DLQ also names the specific AWS SQS and Azure S… DLQ redrive An Amazon SQS operation that moves messages from a dead-letter queue back to a source queue (or… DNS query A client request to resolve a hostname to an IP address. The OS / local client resolver forwards… DNSSEC A suite of IETF extensions (RFC 4033–4035) that adds cryptographic signatures to DNS records. Ea… DoH DNS over HTTPS (RFC 8484): tunnels DNS queries inside HTTPS on port 443, hiding them from on-pat… DOM Document Object Model: a tree of nodes the browser constructs from parsed HTML, where each eleme… dominant term The term in a cost expression that grows fastest and therefore determines the Big-O class once l… DoQ DNS over QUIC (RFC 9250): carries DNS queries directly over QUIC streams on port 853, combining… DoT DNS over TLS (DoT, RFC 7858): a protocol that wraps DNS queries inside a TLS connection on port… double-ended queue A queue where insertion and deletion occur at both ends (front and rear). Same as a deque. Requi… DPoP Demonstrating Proof of Possession (RFC 9449): an OAuth 2.0 mechanism that sender-constrains acce… DSCP Differentiated Services Code Point: a 6-bit field in the IP header (RFC 2474) that marks a packe… dual-write problem The problem that arises when a service must write to two separate systems — for example a databa… duplicate detection The process of identifying records, messages, or requests that have already been processed. Comm… dynamic array A resizable array that doubles its allocated capacity when full, copying elements to a new block… dynamic typing A type discipline where the type of a value is tracked at run time by the runtime itself (not at…E
early exit Stopping a loop or function as soon as the answer is known, without processing remaining element… eBPF A Linux kernel subsystem that allows sandboxed programs to run safely in kernel space without mo… ECDHE Elliptic-Curve Diffie-Hellman Ephemeral: a key-agreement algorithm used in TLS where both sides… ECH Encrypted Client Hello (RFC 9849): a TLS 1.3 extension that encrypts the inner ClientHello — inc… ECMP Equal-Cost Multi-Path routing: when the routing table contains multiple next-hops for the same d… edge case An input or state that lies at the extreme boundary of valid input space — empty collections, ze… edge worker A short-lived compute function executed inside a CDN point-of-presence rather than in a central… effectively-once An end-to-end processing guarantee achieved by combining at-least-once delivery with idempotent… Election Safety A Raft safety property stating that at most one leader can be elected in any given term. It is e… election timeout In Raft, the interval a follower waits without receiving a heartbeat before declaring itself a c… element size The fixed number of bytes one array element occupies. Because every element of an array shares o… encapsulation An object-oriented principle that bundles data and the methods that operate on it into a single… encoding A shared convention that assigns meaning to a bit pattern. The same sequence of bits can represe… enqueue To add an element to the rear of a queue. In a FIFO queue, enqueue inserts the new element at th… error condition A situation a program reaches that it cannot continue past with its normal logic — a missing fil… escape analysis A compiler analysis that proves an object never leaves the function that created it — so it can… ESI Edge Side Includes: an XML-based markup language (W3C submission, 2001) that lets a CDN or rever… event loop The mechanism that runs callbacks: a callback queue plus a loop that, whenever the call stack is… exactly-once A delivery guarantee that each message is received and processed by the consumer exactly one tim… exactly-once processing An application-level guarantee that each input message causes exactly one state change or side-e… exception The runtime mechanism that responds when an error is raised: it stops normal control flow — the… exception handler A block of code written to catch a raised exception and recover from it — in JavaScript, a catch… expand-contract migration A three-phase zero-downtime schema change pattern: expand (add new columns/tables alongside old… exponential backoff A retry strategy where the wait time before each successive attempt doubles (or grows by a fixed… exponential output A problem property where the number of valid outputs grows as 2ⁿ with input size n — generating… exponential time A time complexity class where running time grows as c^n for some constant c > 1, most commonly O… extract minimum A priority queue operation that removes and returns the element with the smallest (or in extract…F
factorial output The output of a factorial calculation: n! = n × (n−1) × … × 1. Factorial values grow faster than… factorial time A time complexity class O(n!) where the number of operations grows as the factorial of the input… false sharing False sharing occurs when two or more CPU cores repeatedly modify independent variables that hap… FAPI 2.0 Financial-grade API 2.0: an OpenID Foundation security profile built on OAuth 2.0 and OIDC, desi… fast and slow pointers A two-pointer technique (Floyd's cycle detection / tortoise-and-hare) where a slow pointer advan… FCP (first contentful paint) First Contentful Paint: a browser performance metric that records the time from navigation start… feasibility check A test that determines whether a candidate solution satisfies all constraints before committing… FeedbackVector A per-function array V8 allocates to record runtime type feedback — one slot per IC site (proper… fencing token A monotonically increasing token number issued by a lock service each time a client acquires a d… fetch waterfall A performance pattern where multiple network requests are issued sequentially — each waiting for… FIB A Fibonacci number is a member of the sequence defined by F(0)=0, F(1)=1, F(n)=F(n−1)+F(n−2): 0,… fiber A transmission medium made of thin glass or plastic strands that carry data as pulses of light u… field A named slot inside an object, also called a property. A field is a key-value pair: the key is t… FIFO First In, First Out: an ordering discipline where the element inserted earliest is the first to… fillfactor A storage parameter setting how full a page may get before a new one is allocated; values below… firewall A network security device that inspects packets and enforces a policy of allow or deny. Stateles… flame graph A stack-trace visualization invented by Brendan Gregg in which sampled call stacks are merged an… follower In Raft, a passive cluster member that accepts log entries from the leader and applies them to i… forced synchronous layout A browser performance problem where JavaScript reads a layout property (e.g. offsetWidth, getBou… forward error correction Forward error correction: a technique where the sender adds redundant packets derived from sourc… forward secrecy A property of a key-agreement protocol whereby a compromise of the server's long-term private ke… forwarding table A data structure in a router's forwarding plane (also called FIB, Forwarding Information Base) t… frame A single rendered image in the browser's display pipeline, produced once per refresh cycle (16.6… frequency counting The pattern of counting how many times each value appears in a dataset using a hash map. One O(n… frequency map A hash map where keys are values from the input and counts (integers) are the values. Built in o… from_collapse_limit How many subquery items the planner will flatten into the parent query's join tree before leavin… front A pointer to the first (oldest) element in a queue. Dequeue operations remove from the front. In… full jitter A retry backoff strategy where the delay before each attempt is drawn uniformly at random from z… functional dependencies (extended statistics) An extended-statistics object telling the planner that one column's value determines another's,…G
garbage collection Automatic memory management performed by a runtime system: the garbage collector (GC) periodical… generic plan A prepared-statement plan compiled once, parameter-agnostic, and reused for every execution — tr… GeoDNS A DNS technique where the authoritative server returns different A/AAAA records based on the geo… GEQO (genetic query optimizer) PostgreSQL's heuristic join-ordering strategy: for queries with many joins it uses a genetic/evo… geqo_threshold The join count at which PostgreSQL switches from exhaustive join-order search to the genetic opt… GraphQL A query language for APIs and a server-side runtime, originally developed at Facebook, where the… GraphQL introspection A built-in GraphQL mechanism that lets clients query the schema itself using meta-fields __schem… GraphQL resolver A function attached to a GraphQL schema field that returns the field's value when a query is exe… GREASE Generate Random Extensions And Sustain Extensibility (RFC 8701): a technique where TLS clients a… greater than One number is greater than another when it sits further right on the number line. Written with t… group key A computed value assigned to each item in a grouping operation; items that compute the same key… grouping A hash-map pattern where the value is a list (not a count): for each item, compute a group key,… growth rate The asymptotic rate at which an algorithm's resource cost (time or space) increases as input siz…H
handshake An initial exchange of messages between two parties that establishes a shared context before dat… happens-before A formal ordering guarantee between two operations: if A happens-before B, then B is guaranteed… introduced 1 used hardware performance counter A hardware register inside the CPU's Performance Monitoring Unit (PMU) that counts low-level mic… hardware prefetcher A dedicated hardware unit inside the CPU that monitors memory access patterns and speculatively… hash function A deterministic function that maps an arbitrary key to a fixed-range integer (the hash code), us… hash map A hash-table-backed key-value store that supports average O(1) insert, lookup, and delete. Unlik… hash set A hash-table-backed collection of unique keys with no associated values, supporting average O(1)… hash table A data structure that maps keys to values by applying a hash function to derive an array index,… head The first node in a linked list. All traversal starts from the head, since there is no backward… header A named key-value metadata field transmitted at the start of an HTTP request or response, separa… header compression The technique of reducing the size of HTTP headers sent on the wire. In HTTP/1.1 headers are pla… heap PostgreSQL's row-oriented table storage: rows live in 8 KB pages with tuple headers, a null bitm… heartbeat A periodic message a node sends to signal that it is still alive. In Raft the leader broadcasts… hidden class (Map/Shape) An internal V8 structure (called Map in V8 source, Shape in SpiderMonkey) that describes an obje… high-level language A programming language that abstracts over the details of a specific CPU — its registers, instru… HKDF HMAC-based Extract-and-Expand Key Derivation Function (RFC 5869): a two-step KDF that first extr… HNSW Hierarchical Navigable Small World — an index for vector similarity search with logarithmic look… hot shard A shard in a distributed database or cache that receives disproportionately more traffic than it… HOT update (heap-only tuple) A PostgreSQL optimization that avoids writing a new index entry when an UPDATE does not change a… hotspot A region of code where a disproportionately large fraction of CPU samples or execution time is c… HPACK The header compression format for HTTP/2 (RFC 7541). HPACK maintains a static table of 61 common… HPKP HTTP Public Key Pinning (RFC 7469): a now-removed browser security header that let a server decl… HSM Hardware Security Module: a tamper-resistant physical device that generates, stores, and uses cr… HSTS HTTP Strict Transport Security (RFC 6797): a response header (Strict-Transport-Security) that in… HTTP frame The basic unit of communication in HTTP/2 (RFC 9113): a 9-byte header (3 bytes length, 1 byte ty… HTTPS record A DNS resource record type (RFC 9460) that publishes HTTPS connection parameters — supported ALP… hybrid logical clock (HLC) A timestamp combining a logical counter with wall-clock time, giving distributed nodes a consist… hydration The client-side process where a JavaScript framework (React, Vue, etc.) attaches event listeners… hydration mismatch An error that occurs during hydration when the HTML the browser received from the server differs… hypothesis In debugging, a specific, testable claim about where a program's behaviour diverged from what wa…I
ICMP Internet Control Message Protocol (RFC 792): a companion to IP that carries error and diagnostic… id_token A signed JWT defined by OpenID Connect that an authorization server returns alongside an access… idempotency The property of an operation that produces the same result whether applied once or multiple time… Idempotency-Key A unique client-supplied token — typically a UUID — sent in the Idempotency-Key HTTP header on a… idempotent producer A message producer that guarantees each logical message is written to a log or queue exactly onc… idle_in_transaction_session_timeout A setting that terminates a session holding a transaction open but doing nothing — preventing it… Ignition (V8 interpreter) V8's bytecode interpreter, first enabled in V8 5.3 / Chrome 53 (for low-memory Android devices)… immutable A value or object whose state cannot be changed after creation. Immutable data eliminates a clas… implicit grant (removed) A former OAuth 2.0 flow in which the authorization server returned an access token directly in t… in place A property of an algorithm that transforms its input using only a constant (O(1)) or at most O(l… in-place change A modification that overwrites an existing memory cell at the same address, replacing its conten… in-place sort A sorting algorithm that rearranges elements within the original array using O(1) or O(log n) ex… inbox pattern A consumer-side deduplication pattern where a service persists an incoming event's unique ID to… index An auxiliary data structure — most commonly a B-tree — maintained alongside a table to speed up… indirection Storing the address of a value rather than the value itself, so a cell points at the data instea… inline cache (IC) A per-call-site optimization where V8 caches the hidden class it last saw and the corresponding… input and output The data supplied to a program (input) and the data it produces (output). Precise definition of… input bound A lower bound on algorithm complexity determined by the size of the input itself: any algorithm… insert To add an element to a priority queue. In a binary heap, insert() adds the element at the end an… insertion sort A comparison-based sorting algorithm that builds the sorted result one element at a time by shif… InstallSnapshot A Raft RPC the leader uses to transfer a complete state-machine snapshot to a follower that has… instrumentation profiler A profiler that injects timing probes into every function entry and exit point at compile time o… integer overflow What happens when an arithmetic result is too large to fit in the fixed number of bits a type re… interface vs implementation The two sides of an abstraction. The interface is the visible surface a user depends on — for a… interpreter A program that reads and executes source code (or bytecode) statement by statement at run time,… IPC (instructions per cycle) Instructions per cycle: the average number of instructions a CPU core retires in one clock cycle… ISN (Initial Sequence Number) Initial Sequence Number: the 32-bit value a TCP endpoint picks for its first byte when opening a… isolation level A setting that controls how much a transaction is shielded from concurrent changes made by other… ISR (Incremental Static Regeneration) A Next.js rendering strategy that serves a pre-built static page instantly and regenerates it in… iss claim In OIDC and OAuth 2.0, the issuer is the case-sensitive HTTPS URL that uniquely identifies an au… iteration One pass through a loop body. If a loop runs 10 times, it performs 10 iterations. In array trave…J
JA3 A TLS client fingerprinting method created at Salesforce in 2017 that extracts selected numeric… JA4 A TLS client fingerprinting suite developed by FoxIO as the successor to JA3, using a sortable a… JAR (RFC 9101) JWT-Secured Authorization Request (JAR, RFC 9101): an OAuth 2.0 extension that packages authoriz… JIT (just-in-time compilation) A hybrid execution strategy in which the runtime compiles frequently executed bytecode or interp… JIT compilation PostgreSQL compiles expression evaluation in scan, join, and aggregate nodes to machine code at… JIT warmup The ramp-up period after a JavaScript process starts during which functions execute in the inter… jitter Random variation added to a retry delay to prevent synchronized bursts. Without jitter, every cl… join_collapse_limit The join count above which the planner stops reordering explicit JOINs and (with geqo_threshold)… joint consensus The Raft mechanism for safely changing cluster membership. When transitioning from configuration… JWKS JSON Web Key Set: a JSON document containing an array of public keys (each in JWK format) that a… JWT JSON Web Token (RFC 7519): a compact, URL-safe token format that encodes a set of claims as a JS…K
Kafka idempotent producer A Kafka producer configured with enable.idempotence=true that receives a unique producer ID (PID… Kafka transactions A Kafka feature (introduced in KIP-98) that lets a producer write to multiple partitions atomica… Keep-Alive An HTTP or TCP mechanism that holds a connection open between requests, avoiding the cost of a n… key-value pair A key together with the value stored under it. An object is a collection of key-value pairs: eac… KIP-98 Kafka Improvement Proposal 98, merged in Kafka 0.11.0, which introduced the two primitives that… kTLS Kernel TLS (kTLS): a Linux kernel feature that moves TLS record encryption and decryption from u…L
L1 cache The first and fastest level in the CPU cache hierarchy, private to each core. L1 is split into a… L2 cache The second level of the CPU cache hierarchy, sitting between L1 and L3. L2 is larger and slower… L3 cache The last level of on-die CPU cache, shared across all cores on the same socket. L3 is the larges… latency The time elapsed from initiating an operation to receiving its result — for example, from sendin… layout The browser pipeline step that computes the exact position and size of every visible element by… layout thrash A performance failure where JavaScript alternates reading and writing geometry properties within… LCP (Largest Contentful Paint) Largest Contentful Paint: a Core Web Vital that measures the render time of the largest visible… Leader Append-Only A Raft safety property: a leader never overwrites or deletes entries in its own log — it only ap… Leader Completeness A Raft safety property: if a log entry is committed in a given term, it is present in the logs o… leader lease A time-bounded agreement among a Raft majority that the current leader remains the only leader f… leaky abstraction An abstraction that fails to fully hide the layer below it, so implementation detail becomes vis… learner (non-voting) A Raft cluster member that receives replicated log entries from the leader but does not count to… less than One number is less than another when it sits further left on the number line. Written with the <… let declaration A variable declaration using the `let` keyword that reserves a memory cell, names it, and allows… libpq PostgreSQL's C client library implementing the frontend/backend wire protocol; psql, PgBouncer,… linear time A time complexity class O(n) where the number of operations grows proportionally to the input si… linked list A sequential data structure where elements are stored in nodes, each holding a value and a point… linker A tool that combines multiple object files and library archives into a single executable binary.… list depth The maximum nesting level of a recursive list structure. A flat list has depth 1; each additiona… load factor In a hash table, the ratio of items to buckets: α = count / size. Higher load factors lead to lo… loader (OS loader) The operating-system component that reads an executable file from disk, creates a new process wi… local scope The scope that is limited to a single function body. A variable declared inside a function has l… local variable A variable declared inside a function body. Its scope is limited to that function body, and its… Log Matching A Raft safety property composed of two guarantees: (1) if two log entries in different servers h… logarithmic time A time complexity class O(log n) where each step reduces the remaining problem size by a constan… logic gate A hardware component that computes one boolean operation. Built from transistors, it takes one o… logical AND A boolean operation that returns true (1) if and only if both inputs are true (1); returns false… logical NOT A boolean operation that takes one input and returns its inverse: NOT 1 = 0, NOT 0 = 1. Also cal… logical OR A boolean operation that returns true (1) if at least one input is true (1); returns false (0) o… logical replication Streaming row-level changes (not raw disk blocks) from one PostgreSQL database to another; the b… Long Animation Frames (LoAF) The Long Animation Frames API — a PerformanceObserver entry (Chromium, 2023+) reporting any fram… introduced 1 used loop invariant A property that holds true before every iteration of a loop and is preserved by each iteration.… lost update A concurrency anomaly where two transactions read the same value, each computes an update indepe…M
macrobenchmark A benchmark that measures end-to-end performance of complete user flows — startup time, scroll f… Maglev (V8 mid-tier JIT) V8's mid-tier optimizing JIT compiler, sitting between Sparkplug (fast baseline) and TurboFan (s… max-heap A heap where the parent node is always greater than or equal to its children. The root always co… maxReceiveCount An Amazon SQS redrive policy setting that controls how many times a consumer may receive a messa… megamorphic IC An inline-cache state reached when a call site has seen more than four distinct object shapes. V… memcache lease A mechanism introduced in Facebook's Memcached deployment (NSDI 2013) to prevent two cache patho… memory cell The smallest individually addressable unit of RAM, typically one byte (8 bits). Each cell has a… merge The combine step of merge sort: given two sorted subarrays, produce a single sorted array by rep… merge sort A divide-and-conquer sorting algorithm that recursively splits an array into halves, sorts each… MESI cache coherency A cache coherency protocol used in multi-core CPUs to keep private L1/L2 caches consistent. Each… metastable failure A self-sustaining system collapse where a transient trigger (e.g. a traffic spike or a cache flu… method A function that is stored as a field of an object and operates on the data of that same object.… microbenchmark A benchmark that measures the performance of a single isolated function or code block, deliberat… min-heap A heap where the parent node is always less than or equal to its children. The root always conta… ML-KEM Module-Lattice-Based Key-Encapsulation Mechanism (NIST FIPS 203, 2024): a post-quantum KEM deriv… mnemonic A short, human-readable abbreviation that stands for a machine-code operation in assembly langua… modulation The process of encoding information onto a carrier signal by varying one or more of its properti… module A unit of code that groups related definitions behind a boundary. A module exposes a public inte… monomorphic IC An inline-cache state where a call site has seen exactly one object shape. V8 caches the single… monotonic predicate A boolean function f(x) that changes value at most once as x increases — either from false to tr… monotonic stack A stack where elements are maintained in sorted order (increasing or decreasing) by removing ele… most common values (MCV) A statistic storing a column's most frequent values and their frequencies, sharpening selectivit… MSS Maximum Segment Size: a TCP option exchanged in SYN segments that advertises the largest payload… mTLS-bound tokens (RFC 8705) Certificate-bound access tokens (RFC 8705): an OAuth 2.0 mechanism that binds an access token to… MTU Maximum Transmission Unit: the largest IP datagram, in bytes, that a network link can carry with… Multi-Paxos An optimization of basic Paxos for replicating a sequence of commands. A stable leader runs Phas… Multi-Raft An architecture in which a single process runs many independent Raft consensus groups simultaneo… multiplexing A technique for sending multiple independent logical channels over a single shared physical link… MultiXact PostgreSQL's mechanism for tracking a row locked by multiple transactions at once (e.g. SELECT .… MultiXact ID A 32-bit id stored in a tuple's xmax when several transactions hold a shared lock on the row; it… must-staple OCSP Must-Staple (RFC 7633): an X.509 v3 certificate extension that requires the TLS server to i… mutation An in-place change to an existing memory cell: an assignment that overwrites the bit pattern at… MVCC Multi-Version Concurrency Control: each writer creates a new row version and each transaction re…N
n_distinct A per-column statistic estimating the number of distinct values; it drives row-count estimates a… N+1 problem A data-access anti-pattern where code executes one query to fetch a list of N items and then N a… nameserver A DNS server that holds the authoritative records for a zone and answers queries about hostnames… natural number A counting number: 1, 2, 3, and so on. ND Neighbor Discovery (RFC 4861): the IPv6 protocol that replaces ARP and ICMP Router Discovery. No… negative caching Storing the fact that a lookup produced no result, so subsequent identical queries are answered… neighbor (adjacent vertex) A vertex v is a neighbor of u if an edge exists between them. In a directed graph, v is a neighb… next greater element For each element in an array, the next element to its right that is larger than it. If no such e… next pointer A field in a node that stores the memory address of the next node in a linked list. The last nod… node A single unit in a linked list. Contains a value and a pointer to the next node. The first node… non-blocking call A call to a slow device that does not wait for the work to finish. It hands the request to the d… nonce A number used once: a random value included in a cryptographic protocol to guarantee that each m… null (JS) The JavaScript primitive value representing deliberate absence of any object or value. Distinct… NUMA A multiprocessor memory design where each CPU socket has its own local memory, and accessing mem… number (JS) The JavaScript primitive type for all numeric values, stored as a 64-bit IEEE 754 double-precisi…O
O(log n) time Time complexity where each step halves (or reduces by a constant factor) the remaining problem s… OAuth 2.1 OAuth 2.1 (IETF draft): a consolidation of OAuth 2.0 (RFC 6749) and its security best practices… object file The output of compiling or assembling a single source file. An object file contains machine-code… object reference A value stored in a variable's memory cell that is the heap address of an object, not the object… observer effect The distortion of a program's performance characteristics caused by the act of measuring it: ins… OCSP Online Certificate Status Protocol (RFC 6960): a protocol for checking the revocation status of… off-CPU profile A profile that records time a thread spends off the CPU — blocked on I/O, locks, page faults, or… offset How many bytes past a base address a piece of data begins. For an array element, the offset equa… OpenID Connect OpenID Connect: an identity layer on top of OAuth 2.0 that adds user authentication to OAuth's a… operation batching A GraphQL transport technique where the client sends multiple operations in a single HTTP reques… operations per second A throughput metric counting how many discrete operations a system completes in one second. Used… opposite ends A two-pointer pattern where one pointer starts at index 0 and the other at the last index, then… optimistic update A UI pattern where the client applies a state change immediately — before the server confirms —… origin shield An intermediate CDN caching tier placed between edge PoPs and the origin server. When multiple e… Orinoco GC The codename for V8's modern garbage collector, which replaced a stop-the-world design with para… outbox pattern Write a domain change and an event row to an outbox table in one transaction; an async worker la… overwrite To replace the current bit pattern in a memory cell with a new value, destroying the previous co…P
PACELC theorem An extension of the CAP theorem proposed by Daniel Abadi to describe distributed system trade-of… packet A unit of data routed through a network, consisting of a header containing control fields (sourc… paint The browser pipeline step that converts the layout tree into a list of drawing commands (a displ… PAR (RFC 9126) Pushed Authorization Request (RFC 9126): an OAuth 2.0 extension where the client sends the full… parallelism Many tasks literally running at the same instant, which requires multiple cores — one instructio… parameter A named variable declared in a function signature that receives its value from the caller's argu… partial solution An incomplete candidate solution being built during backtracking—it may satisfy some constraints… partition A subroutine in quicksort that rearranges elements in a subarray so that all elements smaller th… pass-by-value A calling convention where the argument's value is copied into the callee's stack frame as a par… path A sequence of vertices where consecutive vertices are connected by edges. A simple path visits e… Paxos A family of protocols for reaching consensus in a cluster of crash-prone nodes, introduced by Le… peek To view the highest-priority element without removing it from a priority queue. In a binary heap… perf_event_open A Linux system call that opens a file descriptor for a hardware or software performance event on… PerformanceLongTaskTiming A PerformanceObserver entry type that reports any main-thread task longer than 50 ms — the brows… permutation An ordered arrangement of all elements of a set. A set of n distinct elements has n! permutation… persisted queries A GraphQL security and performance technique where operation strings are pre-registered on the s… PFS (Perfect Forward Secrecy) Perfect Forward Secrecy: the same property as forward secrecy — a compromise of the server's lon… pg_repack A PostgreSQL extension that removes table and index bloat online by copying rows to a shadow tab… PgBouncer A lightweight connection pooler that multiplexes thousands of client connections onto a small se… PGO (profile-guided optimisation) Profile-guided optimisation (PGO) is a compiler technique that feeds runtime execution data from… phantom read A SQL-standard concurrency anomaly where a transaction re-executes a range query and finds rows… pipelining An HTTP/1.1 feature that allows a client to send multiple requests on a persistent TCP connectio… pivot An element selected from a subarray to drive the partition step in quicksort. After partitioning… PKCE Proof Key for Code Exchange (RFC 7636): an OAuth 2.0 extension that defends against authorizatio… place value The value a digit carries because of where it sits in a number: the same digit means ones, tens,… PMTUD Path MTU Discovery (RFC 1191 for IPv4, RFC 1981 for IPv6): a mechanism that finds the smallest M… poison pill A message that a consumer can never process successfully, causing it to crash or throw on every… polymorphic IC An inline-cache state where a call site has seen between two and four distinct object shapes. V8… polymorphic inlining Inlining a called function directly at the call site when the engine has seen a small, fixed set… POP Point of Presence: a physical CDN or cloud facility housing edge servers, routers, and interconn… postgres_fdw A foreign-data-wrapper extension that lets one PostgreSQL query tables in a remote PostgreSQL in… postmaster The supervisor process of a PostgreSQL instance: it listens for connections, forks a backend pro… power set The set of all subsets of a given set, including the empty set and the set itself. A set of n el… pprof pprof is Google's profiling data format (a gzip-compressed protocol buffer) and the accompanying… pre-vote A Raft extension that adds a phase before a real election: a candidate first checks whether a ma… precomputation Computing a result once in advance and storing it for later reuse, trading upfront time and spac… predicate lock An SIREAD lock acquired by PostgreSQL's SSI engine on every tuple, page, or relation a serializa… prefetch A technique where a cache line is loaded into CPU cache before the processor explicitly requests… prefix array An array where each element at index i stores the cumulative sum (or other aggregate) of element… prefix sum A technique where an array is preprocessed in O(n) time so that the sum of any contiguous subarr… premature optimisation Knuth's warning (1974): "premature optimization is the root of all evil" — spending engineering… preprocessing A one-time computation over input data that builds an auxiliary structure, trading upfront time… primitive copy The behaviour when a primitive value is assigned to a variable: the actual bit pattern is copied… primitive type A type representing a single, indivisible value that cannot be decomposed into smaller typed par… priority queue An abstract data type that stores elements and allows extraction of the element with the highest… procarray A shared-memory array of all active backend processes; backends read it to build an MVCC snapsho… profile A profile is a dataset that records where a program spends resources — CPU cycles, memory alloca… program state The complete collection of current values held by all live variables at a specific instant durin… pruning In backtracking, the act of identifying when a partial solution cannot lead to a valid answer an… PSK Pre-Shared Key: a symmetric key distributed to communicating parties out of band before the sess… Pyroscope Pyroscope (now Grafana Pyroscope) is an open-source continuous profiling database that stores CP…Q
QAM Quadrature Amplitude Modulation: a digital modulation scheme that encodes data by varying both t… QPACK QPACK (RFC 9204): the header compression format used in HTTP/3, replacing HPACK. Unlike HPACK wh… quadratic time An algorithm runs in quadratic time, O(n²), when doubling the input size roughly quadruples the… query cost An arbitrary unitless number the PostgreSQL planner assigns to each execution plan node, anchore… queue A data structure that stores elements in first-in, first-out (FIFO) order: add elements to the b… QUIC QUIC (RFC 9000): a general-purpose transport protocol built on UDP that integrates TLS 1.3 encry… quicksort A divide-and-conquer sorting algorithm that picks a pivot, partitions the array into elements le… quorum The minimum number of nodes in a distributed system that must acknowledge an operation for it to…R
radio A wireless physical-layer link that carries data as modulated electromagnetic waves over a radio… Raft A consensus algorithm designed explicitly for understandability, introduced by Ongaro and Ouster… raise an exception To trigger the exception mechanism in response to a detected error condition. "Raise" and "throw… range query A question about a contiguous range of elements, such as 'what is the sum of elements from index… raster The step where the browser executes paint commands to produce actual pixel bitmaps for each comp… React DevTools Profiler A panel in the React DevTools browser extension that records each render commit with per-compone… React Server Components (RSC) React Server Components: a React architecture where components marked without "use client" run e… React Suspense A React component that wraps a subtree and renders a fallback UI while any child component is no… READ COMMITTED The default PostgreSQL isolation level. Each statement within a transaction takes a fresh snapsh… ReadIndex A Raft optimization that allows the leader to serve linearizable reads without writing a log ent… rear A pointer to the last (most recently added) element in a queue. Enqueue operations add to the re… recursion When a function calls itself to solve a smaller version of the same problem. Requires a base cas… recursion tree A tree diagram where each node represents a single function call, edges represent call relations… recursive case The part of a recursive function that calls itself on a smaller input, making progress toward th… recursive resolver A DNS server that accepts a query from a client, walks the DNS delegation hierarchy on the clien… redirect_uri The URI to which the OAuth authorization server redirects the user-agent after authorization, ca… reference semantics The assignment behaviour for objects and arrays: the variable's cell receives a copy of the refe… reflow An older WebKit and Gecko name for the layout step: the browser recalculates every affected elem… refresh token A long-lived credential issued alongside an access token that allows a client to obtain a new ac… refresh token rotation Refresh token rotation: a security policy where each use of a refresh token immediately invalida… relaxed memory model A concurrency model where threads may observe memory writes in different orders unless explicit… introduced 1 used render tree A tree the browser constructs by combining the DOM and CSSOM, retaining only the visible nodes e… repaint A browser rendering cycle triggered when a visual property changes but element geometry is unaff… REPEATABLE READ A PostgreSQL isolation level where a transaction takes a single snapshot at the start of its fir… replay attack An attack in which a valid, previously captured message or credential is retransmitted to deceiv… replicated state machine An architecture where each node in a cluster maintains an identical state machine driven by the… request coalescing A general CDN and proxy behaviour where concurrent cache-miss requests for the same URL at one e… request collapsing (Fastly) Fastly's name for the same deduplication behaviour: when a cacheable object is being fetched fro… request fingerprint A compact hash or signature derived from a set of observable request attributes — IP address, Us… RequestVote The Raft RPC sent by a candidate to solicit votes during an election. The message carries the ca… resolver A DNS server that receives queries from stub resolvers on end-user devices and resolves them to… resolver lookahead A GraphQL resolver optimization where a resolver inspects the query AST via the info argument to… Resource Indicators (RFC 8707) An OAuth 2.0 extension (RFC 8707) that adds a resource parameter to authorization and token requ… retransmission TCP resending a segment that was not acknowledged within the retransmission timeout (RTO). TCP d… retransmit To resend a TCP segment that was not acknowledged. The sender retransmits when the retransmissio… retry budget A resilience policy that caps the total rate of retries a service may emit as a fraction of the… retry storm A failure mode where many clients simultaneously retry failed requests against a recovering serv… Retry-After An HTTP response header that tells a client how long to wait before retrying a request. Used wit… return value The value produced by a function and handed back to the caller when the function's return statem… RGB Red-Green-Blue colour encoding. Each pixel stores three intensity values — one per channel — typ… router A Layer 3 network device that forwards IP packets between networks. For each arriving packet, th… routing table A data structure in a router that maps destination IP prefixes to next-hop addresses and outgoin… row estimate disaster A query plan failure caused by the PostgreSQL planner grossly misjudging the number of rows a no… row-level security (RLS) PostgreSQL policies that filter which rows a role may read or write — an in-database alternative… RRSIG RRSIG (Resource Record Signature): a DNSSEC record that holds the digital signature for an RRset… RSC Payload The serialized React Flight wire format that a React Server Components framework streams from se… RTT Round-trip time: the elapsed time from sending a packet to receiving its acknowledgment. RTT dri… RUM (real user monitoring) Real User Monitoring (RUM) collects performance and error data from actual browser or mobile ses… runtime system The support infrastructure that a language implementation provides alongside a compiled or inter…S
sampling (audio) The process of measuring a continuous signal (typically air pressure for audio) at discrete, equ… sampling profiler A sampling profiler measures program behavior by periodically interrupting execution — typically… Scavenger (V8 young-gen GC) V8's parallel young-generation garbage collector, part of the Orinoco GC. It runs a semispace co… scope The region of source code in which a name (variable, parameter, function) is visible and usable.… sea-of-nodes IR A graph-based compiler intermediate representation where data and control dependencies are nodes… search space The subset of elements currently being searched or considered. Binary search repeatedly halves t… seen set A hash set that stores values encountered while traversing data. For each new value, check if so… SELECT FOR UPDATE A PostgreSQL SELECT clause that acquires an exclusive row-level lock on each returned row, block… selection sort An in-place sorting algorithm that repeatedly finds the minimum element in the unsorted portion… self-time In sampling profilers such as pprof and cProfile, the self time (flat time) of a function is the… sender-constrained tokens A property of an access token that cryptographically binds it to the client that requested it, r… sequence number A 32-bit field in a TCP segment (RFC 793) that labels the first byte of payload data in that seg… SERIALIZABLE The strictest SQL isolation level, guaranteeing that concurrent transactions produce the same re… serialization failure (SQLSTATE 40001) An error (SQLSTATE 40001) PostgreSQL raises when SSI or REPEATABLE READ detects that committing… Server Function An async function marked with the 'use server' directive that executes exclusively on the server… Server Push An HTTP/2 feature where the server sends a PUSH_PROMISE frame announcing a resource, then delive… session ticket A TLS session resumption mechanism in which the server encrypts the session state and sends it t… SETNX A Redis command (SET if Not eXists) that writes a key only when it is absent, returning 1 on suc… shared_buffers PostgreSQL's main in-memory cache of table and index pages, shared by all backends; its size sha… shared-tenant proxy A reverse proxy that serves multiple independent tenants from the same infrastructure — terminat… short circuit Stopping evaluation as soon as the result is determined. Example: `arr.some(x => x < 0)` stops a… signal-to-noise ratio In observability and alerting, signal-to-noise ratio describes the proportion of actionable, mea… SIMD A CPU instruction-set feature that applies one operation to multiple data elements packed into a… single-flight A concurrency pattern, canonically implemented in Go's golang.org/x/sync/singleflight package, t… sliding window An algorithm technique that maintains a contiguous range of elements — the window — and advances… Smi (small integer) In the V8 JavaScript engine, a Smi (small integer) is an integer in the 31-bit signed range (32-… snapshot A consistent, point-in-time view of data captured at a specific moment. In MVCC databases a snap… snapshot isolation A concurrency control method where each transaction reads from a consistent snapshot taken at it… SNI Server Name Indication (RFC 6066): a TLS extension in which the client includes the target hostn… SoA (structure of arrays) Structure of Arrays: a memory layout where each field of a record type is stored in its own cont… sorted A collection is sorted when every element satisfies the ordering relation with its successor — f… sorted array An array arranged in non-decreasing order (or non-increasing, depending on the sort direction).… sorting The process of rearranging the elements of a collection so that they satisfy a total order — typ… source map A file mapping minified production code back to original source lines, so a stack trace or profi… space complexity A function describing how much extra memory an algorithm uses as input size n grows. Expressed i… Sparkplug (V8 baseline JIT) V8's non-optimizing baseline JIT compiler, sitting between Ignition (interpreter) and Maglev (mi… specification A precise, implementation-independent description of what a system, protocol, or interface must… SPIFFE Secure Production Identity Framework for Everyone: an open standard for issuing cryptographic wo… SPIRE SPIFFE Runtime Environment: the reference implementation of the SPIFFE specification. A SPIRE Se… split brain A failure mode in a distributed cluster where a network partition causes two or more subsets of… SQS visibility timeout An Amazon SQS parameter that controls how long a message remains invisible to other consumers af… SSA (Static Single Assignment) A compiler intermediate-representation form where every variable is assigned exactly once, makin… SSG (Static Site Generation) A rendering strategy where pages are compiled to static HTML, CSS, and JavaScript at build time… SSI (Serializable Snapshot Isolation) Serializable Snapshot Isolation — the algorithm behind PostgreSQL's SERIALIZABLE level since ver… SSR (Server-Side Rendering) A rendering strategy where the server generates a complete HTML document for each incoming reque… stable sort A sorting algorithm is stable if it preserves the original relative order of elements that compa… stack frame The block of call-stack memory allocated for a single function invocation, holding that call's l… stack overflow A runtime error that occurs when a program exhausts the fixed-size call stack, most often becaus… stack trace A snapshot of the call stack at the moment an exception is raised: the ordered list of frames fr… stack unwinding The runtime's walk down the call stack after an exception is raised: starting from the frame tha… stacking context An element whose descendants paint together as one self-contained z-order group; that group as a… stale-if-error A Cache-Control extension (RFC 5861) that allows a cache to serve a stale stored response when t… stale-while-revalidate A Cache-Control extension (RFC 5861) and HTTP caching strategy: the cache serves a stale respons… standard library The collection of built-in functions, data structures, and modules that ships with a programming… start index In combination/permutation backtracking, a parameter that controls which elements can be conside… state machine A computational model that transitions between a finite set of states in response to inputs. In… State Machine Safety A Raft safety property (Figure 3 of the Raft paper): if a server has applied a log entry at a gi… state param The state parameter in an OAuth 2.0 authorization request (RFC 6749 §4.1.1): an opaque random va… stateful program A program that stores values across multiple steps and modifies them over time, so its behaviour… statefulness The property of a service that retains client context between requests — session data, in-flight… stateless reset A QUIC mechanism (RFC 9000 §10.3) that lets an endpoint terminate a connection even after losing… static typing A type discipline where the type of every variable is known at compile time. The compiler checks… STEK (Session Ticket Encryption Key) Session Ticket Encryption Key: the symmetric key a TLS server uses to encrypt and authenticate s… step count The step count of an algorithm is the number of primitive operations — assignments, comparisons,… store operation A CPU instruction that writes a value from a register into a memory cell at a specified address.… stream A sequence of data elements — bytes, events, or records — made available incrementally over time… stream-level loss isolation A QUIC property whereby a lost packet stalls only the stream it belongs to, leaving all other st… string A sequence of characters treated as a single value. In most high-level languages strings are len… string (JS) The JavaScript primitive type representing a sequence of Unicode code points. Stored internally… style recalc The browser pipeline step in which the engine matches every CSS selector against every affected… sub claim The subject claim in a JWT or OIDC token: a string that uniquely identifies the principal (typic… subarray A contiguous slice of an array defined by a start and end index, containing only elements that a… subgraph An independently deployed GraphQL service that owns a slice of the federated schema in Apollo Fe… subset Set A is a subset of set B (written A ⊆ B) if every element of A is also in B. The empty set is… supergraph The unified GraphQL schema produced by composing multiple Apollo Federation subgraphs. It is not… SVCB record SVCB (Service Binding) record: a DNS resource record type (RFC 9460) that publishes connection p… swap Exchange the values of two variables or array elements in place: [a, b] = [b, a]. Used in revers… SWR library A React data-fetching library by Vercel whose name is derived from stale-while-revalidate. The u… SYN The TCP segment flag that initiates a connection. A client opens a TCP connection by sending a s… SYN cookies A defense against SYN-flood attacks (RFC 4987) in which the server encodes connection state into… synchronous The approach where a program sends a request to a slow device and then stops and waits for the a…T
t_xmax A system column in every PostgreSQL heap tuple that holds the transaction ID of the transaction… t_xmin A system column in every PostgreSQL heap tuple that holds the transaction ID of the INSERT or UP… TanStack Query A framework-agnostic server-state library (also known as React Query) for TypeScript/JavaScript… TCP segment The Protocol Data Unit (PDU) of TCP: a header plus a payload of application bytes. The 20-byte m… term (Raft) In Raft, a monotonically increasing integer that acts as a logical clock and election epoch. Eac… TFO (TCP Fast Open) TCP Fast Open (RFC 7413): an extension that allows a client to include application data in the S… thread A single, ordered stream of instructions being executed — one program counter advancing through… throughput The volume of work a system completes per unit of time — for example, requests per second or byt… thundering herd A failure mode where a large number of processes or requests simultaneously contend for the same… time budget A time budget is a maximum allowed execution time assigned to a task, request, or rendering phas… time–space tradeoff A choice where an algorithm can reduce time by using more memory, or reduce memory by taking mor… TimeoutNow A Raft RPC used to transfer leadership to a designated follower. The current leader first brings… TLB (translation lookaside buffer) An MMU cache that stores recent virtual-to-physical address translations. Modern CPUs use a mult… TLD Top-level domain: the rightmost label in a domain name, appearing after the last dot (e.g., .com… TLS Transport Layer Security: the cryptographic protocol that secures most Internet traffic. A TLS h… token introspection OAuth 2.0 Token Introspection (RFC 7662): an endpoint a resource server calls to ask the authori… transaction-mode pool A PgBouncer pooling mode where a server connection is assigned to a client only for the duration… transactional outbox A pattern that solves the dual-write problem: instead of writing to a database and publishing to… traversal The act of visiting every element in a data structure (array, list, tree) in a specific order, u… tree depth The length of the longest path from root to leaf in a tree. In a recursion tree, depth equals th… tri-color marking A garbage-collection marking scheme that partitions objects into white (unreached), grey (reache… trusted documents A GraphQL security technique where the server maintains an allowlist of pre-approved operation d… truth table A table listing every possible combination of inputs to a boolean operation and the output it pr… TTFB (time-to-first-byte) Time To First Byte: the elapsed time from a browser sending an HTTP request to receiving the fir… TTL TTL (time to live) bounds how long data stays valid. For a cached entry or DNS record it is a ti… TTL jitter A caching technique that adds a random offset to a cache entry's TTL so that entries populated a… tuple In PostgreSQL, a single physical row version stored in a heap file. Each tuple carries a header… TurboFan (V8 optimising JIT) V8's top-tier optimizing JIT compiler. It reads Ignition's type-feedback vectors and compiles by… Two Generals' Problem A thought experiment proving that it is impossible to achieve guaranteed agreement over an unrel… two pointers An algorithm technique that uses two index variables moving through an array or string — either… two sum A classic problem: find two numbers in an array that add up to a target. The naive solution is O… type An interpretation rule for a bit pattern: it specifies how many bytes the value occupies and how… type error A detected mismatch between the type rule used to store a value and the type rule applied when r… type interpretation The act of applying a type rule to a bit pattern to produce a meaningful value. The same bit pat… type rule The specification of how a bit pattern should be decoded: its size in bytes and the algorithm fo… type safety The property of a program or language system that prevents bits from being read with a different… typeof A JavaScript/TypeScript unary operator that returns a string naming the type of its operand at r…U
undefined (JS) The JavaScript primitive value assigned automatically to a declared-but-not-yet-assigned variabl… undefined behaviour A program operation for which the language gives no guaranteed result — reading past the end of… undirected graph A graph where edges have no direction: edge (u,v) is the same as (v,u). Each edge is bidirection… Unicode A universal character standard that assigns a unique code point (written U+XXXX) to every charac…V
V8 Google's JavaScript engine, used in Chrome and Node.js. It parses, compiles, optimises, and runs… V8 Isolate A self-contained V8 instance with its own heap, garbage collector, and compilation pipeline. Mul… VACUUM A PostgreSQL maintenance command that scans table pages, marks dead tuple slots as reusable, and… VACUUM FULL A PostgreSQL variant of VACUUM that rewrites the entire table and all its indexes into new files… value At the machine level: a pattern of bits stored in one or more consecutive memory cells. At the l… value in memory A value considered as a concrete bit pattern at a specific address in RAM. Contrasted with the a… value semantics The assignment behaviour for primitive types: the actual bit pattern of the value is copied into… variable A named memory cell (or group of cells) whose contents can be read and updated. Consists of two… variable name The source-code identifier used to refer to a variable, such as 'score' or 'count'. The name is… variable value The bit pattern currently stored in the memory cell bound to a variable. Distinct from the varia… Vary header An HTTP response header that lists the request headers a cache must consider when looking up a s… vertex (node) A fundamental unit of a graph, representing an entity. A graph consists of vertices connected by… virtual machine (VM) A software program that emulates a simplified computer — the 'virtual' CPU. Bytecode languages c… visibility map A per-table bitmap marking pages where every tuple is visible to all transactions, letting index… vsync The display's hardware refresh signal — one tick every ~16.67 ms at 60 Hz. The browser aims to c…W
WAL (write-ahead log) PostgreSQL's sequential on-disk log (stored in pg_wal/) where every change is recorded before th… wall-clock time The elapsed real time a process or operation takes from start to finish, as measured by an exter… weighted edge An edge with an associated numeric value (weight), representing cost, distance, or strength. Con… will-change A CSS property that hints to the browser which properties of an element are likely to change, so… window In TCP, the receive window is the amount of buffer space a receiver advertises in each ACK segme… wire The physical or logical transmission medium over which encoded bytes travel between two endpoint… worst case The worst case of an algorithm is the specific input (or class of inputs) of a given size that m… write pointer An index that marks where the next element to keep should be written during an in-place array mo… write skew A concurrency anomaly that arises under snapshot isolation but is not one of the three SQL-stand… write-ahead logging (WAL) Every change is appended to a sequential log before the data pages are written, so an interrupte…X
X25519MLKEM768 A hybrid TLS 1.3 key exchange group that concatenates a classical X25519 ECDHE share with an ML-… XFetch A probabilistic early-expiration algorithm that prevents cache stampedes without locks. Each rea… XID wraparound PostgreSQL transaction ids are 32-bit and eventually wrap; if old rows are not frozen by VACUUM… xmin horizon The oldest transaction ID still needed for visibility by any active transaction, replication slo…Y
Yuasa snapshot-at-the-beginning A concurrent-GC technique that preserves the object graph as it was at the start of marking — so…No terms match.