WAL table configurations

These settings control the Write-Ahead Log (WAL) subsystem, including parallel apply threads, segment rollover, commit squashing, and cleanup of applied WAL files.

cairo.wal.apply.parallel.sql.enabled​

  • Default: true
  • Reloadable: no

When disabled, SQL executed by the WAL apply job always runs single-threaded.

cairo.wal.apply.suspended.tables​

  • Default: none
  • Reloadable: yes

Comma-separated list of table directory names (for example, my_table~3) whose WAL transactions the apply job must not apply, keeping them "hard suspended". Directory names are matched rather than logical names, so the suspension follows the physical table across a rename, and a new table that reuses the name is unaffected. This is the static counterpart to ALTER TABLE ... SUSPEND WAL, whose runtime set is tracked separately. A table listed here stays suspended until it is removed from the list.

cairo.wal.apply.suspended.write.denied​

  • Default: false
  • Reloadable: yes

When enabled, tables suspended from WAL apply (through cairo.wal.apply.suspended.tables or ALTER TABLE ... SUSPEND WAL) also reject new WAL writes with a distinct error, similar to writing to a dropped table. When disabled, suspension only excludes the table from WAL apply while writes keep buffering for later. Must be enabled to use ALTER TABLE ... REBASE WAL, so that suspension makes the table quiescent.

cairo.wal.max.lag.txn.count​

  • Default: 20
  • Reloadable: no

Maximum number of transactions that can be kept invisible when writing to a WAL table. Once reached, a full commit occurs. If not set, defaults to the rounded value of cairo.wal.squash.uncommitted.rows.multiplier.

cairo.wal.purge.interval​

  • Default: 30000
  • Reloadable: no

Period in milliseconds of how often WAL-applied files are cleaned up from disk.

cairo.wal.segment.rollover.row.count​

  • Default: 200000
  • Reloadable: no

Number of rows written to the same WAL segment before starting a new segment. Triggers in conjunction with cairo.wal.segment.rollover.size (whichever threshold is reached first).

cairo.wal.squash.uncommitted.rows.multiplier​

  • Default: 20.0
  • Reloadable: no

Multiplier applied to cairo.max.uncommitted.rows to calculate the limit of rows that can be kept invisible when writing to a WAL table under heavy load, when multiple transactions are being applied. This reduces the number of out-of-order (O3) commits by squashing multiple commits together. Setting it too low can increase O3 commit frequency and decrease throughput. Setting it too high may cause excessive memory usage and increase latency.

wal.apply.worker.affinity​

  • Default: equal to the CPU core count
  • Reloadable: no

Comma-separated list of CPU core indexes.

wal.apply.worker.count​

  • Default: equal to the CPU core count
  • Reloadable: no

Number of dedicated worker threads assigned to handle WAL table data.

wal.apply.worker.haltOnError​

  • Default: false
  • Reloadable: no

Flag that indicates if the worker thread must stop when an unexpected error occurs.