Glossary

Terms

Short definitions. Study pages link the first mention of each term outside code.

• CASCompare-and-swapAn update succeeds only when the current value still matches the version the caller expected.
• CDCChange data captureA stream of row changes, usually read from the database log, for other systems to consume.
• DLQDead-letter queueA side queue for messages a consumer could not process after its retries were used up.
• LSMLog-structured merge-treeWrites land in a memory buffer, flush into sorted runs, and are compacted in the background.
• MVCCMulti-version concurrency controlThe database keeps multiple row versions so a reader can see a snapshot without blocking a writer.
• OLAPOnline analytical processingScans and aggregations over a large history, rather than one row for one user.
• OLTPOnline transaction processingShort reads and writes that back a live application, one business operation at a time.
• P9999th percentileNinety-nine percent of samples are at or below this value. The remaining one percent is the tail.
• RPORecovery point objectiveHow much data you can afford to lose, measured as the time between the last good copy and the failure.
• RTORecovery time objectiveHow long you can afford to be down before the service has to be back.
• SLIService level indicatorA measured signal, such as the share of requests faster than a latency threshold.
• SLOService level objectiveThe target you set for an SLI, such as 99.9% of reads under 50 ms.
• TTFTTime to first tokenHow long a model takes to emit the first output token after the request arrives.
• WALWrite-ahead logChanges are appended to a durable log before the pages they describe are written back.