April 17, 2025 - But in short - with “synchronous_commit=off” (generally used as a performance crutch) Postgres commits are managed by this wal writer process. They are actually not flushed directly to the transaction log (a.k.a. WAL or XLog), but rather just sent to the operating system and fsync (i.e.

1 month ago - 28.3. Write-Ahead Logging (WAL) # Write-Ahead Logging (WAL) is a standard method for ensuring data integrity. A detailed description can be …

1 month ago - The default value is 200 milliseconds (200ms). Note that on some systems, the effective resolution of sleep delays is 10 milliseconds; setting wal_writer_delay to a value that is not a multiple of 10 might have the same results as setting it to the next higher multiple of 10.

January 9, 2026 - Discover the significance of Postgres WAL (Write-Ahead Logging) in maintaining data integrity. Explore their role in robust data backups and crucial WAL configuration concepts.

In the field of computer science, ... the term WAL is used interchangeably with transaction log, and it also refers to the implemented mechanism for writing actions to a transaction log (WAL)....

April 10, 2025 - Rather than writing data modifications directly to disk, PostgreSQL first writes them to the WAL buffer in memory. Then, the WAL writer process periodically flushes this buffer to disk—a process known as a “checkpoint”—to ensure that changes are safely persisted.

May 9, 2025 - In the case the backends have not finished writing to WAL buffer, WAL writer process will wait till the WAL buffer is written before flushing to disk. ... WAL logs are the binary files in which various transactions are stored. These logs are written to disk before the changes are made to the database. PostgreSQL maintains multiple WAL (Write-Ahead Log) files.

January 1, 2012 - Briefly, WAL's central concept is that changes to data files (where tables and indexes reside) must be written only after those changes have been logged, that is, when log records describing the changes have been flushed to permanent storage.

February 11, 2025 - This has dual benefits: it not ... WAL writer is a background process in PostgreSQL that’s tasked with flushing WAL data from memory buffers to disk....

September 18, 2025 - Data written >= 1MB Flush immediately Yes ✅ Yes No 🕒 Wait for wal_writer_delay · Flushing is disabled. WAL is still written, but not fsync’ed — relies on the OS page cache. ⚠️ Dangerous in crashes — WAL not guaranteed to reach disk. Keep default (1MB) unless you have specific storage behavior you’re optimizing for. wal_skip_threshold = 10MB # Default: 2MB (in newer versions) This controls whether PostgreSQL skips WAL logging during bulk operations like:

May 22, 2025 - This guarantees that, even if the system crashes, PostgreSQL can recover to a consistent state. WAL Buffers: In-memory buffers that temporarily hold WAL records before they’re written to disk. WAL Files: On-disk files (in pg_wal/), typically 16MB each, storing the WAL records. WAL Writer Process: ...

March 2, 2026 - It records changes to the database before they are applied, allowing PostgreSQL to recover data and restore the database to its most recent state in case of a crash or failure. Before the introduction of Write-Ahead Logging (WAL) in PostgreSQL, PostgreSQL relied on a simpler mechanism for ensuring data integrity, which was less robust and did not support advanced features like point-in-time recovery and replication.

March 10, 2025 - Log First: PostgreSQL writes the intended changes as WAL records to an append-only log file before modifying any database files (heap or indexes). This includes granular details like the operation type (INSERT, UPDATE, or DELETE), the modified page, and before-and-after states if necessary.

March 2, 2026 - The main configuration file is typically at /etc/postgresql/16/main/postgresql.conf. The wal_level parameter controls what is written to WAL:

July 13, 2024 - In PostgreSQL, the process of writing data to the WAL (Write-Ahead Log) file and the data file follows a specific sequence to ensure data…

May 28, 2020 - How to configure and manage PostgreSQL write-ahead logging (WAL)? What strategy to use for WAL management? Pros and cons of Bounded WAL, Archived WAL and Replication Slots

1 month ago - When track_wal_io_timing is enabled, the total amounts of time XLogWrite writes and issue_xlog_fsync syncs WAL data to disk are counted as write_time and fsync_time in pg_stat_io for the object wal, respectively. XLogWrite is normally called by XLogInsertRecord (when there is no space for the new record in WAL buffers), XLogFlush and the WAL writer, to write WAL buffers to disk and call issue_xlog_fsync.

August 12, 2021 - If the last flush happened less than wal_writer_delay milliseconds ago and less than wal_writer_flush_after bytes of WAL have been produced since, then WAL is only written to the operating system, not flushed to disk. The default value is 200 milliseconds (200ms).