arthrop0d

Brief articles on varied topics.

sql

7 articles tagged sql.

  1. MVCC Snapshots and Row Version Visibility

    How MVCC snapshots choose visible row versions so SQL readers and writers can run concurrently without blocking each other.

    sqldatabasesconcurrency

  2. SQL Query Cardinality Estimation and Histograms

    How SQL planners use table statistics to estimate predicate results and choose scans, joins, and execution strategies.

    sqldatabases

  3. SQL Write-Ahead Logs and Crash Recovery

    A write-ahead log records transaction changes durably before data pages, allowing a SQL database to recover committed work after a crash.

    sqldatabases

  4. MVCC Snapshots and SQL Row Visibility

    How SQL transactions choose visible row versions so readers can use a consistent view while writers update the same data.

    sqldatabasesconcurrency

  5. SQL NULL and Three-Valued Logic

    Understand SQL NULL, UNKNOWN predicate results, and why WHERE, JOIN, and CHECK constraints handle them differently.

    sqldatabases

  6. SQL Selectivity Estimates and Query Plans

    How database planners use histograms to estimate matching rows, and how bad estimates lead to unexpectedly slow scans, joins, and indexes.

    sqldatabasesperformance

  7. Database Write-Ahead Logging and Crash Recovery

    How databases use durable log records to preserve committed transactions and remove incomplete changes after a crash.

    sqldatabases

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