All Your GUCs in a Row: min_wal_size

A deep technical breakdown of PostgreSQL's min_wal_size parameter explains that, contrary to its name, it does not retain WAL for standbys or point-in-time recovery—it is purely a floor on how far the WAL pool can shrink during recycling. The piece walks through how recycling and the max_wal_size autotuner interact, shows via benchmarks that running out of pool forces backends to zero-fill and fsync new 16MB segments while holding WALWriteLock (measured at 21ms per segment, causing p99.9 latency to double), and covers edge cases like wal_recycle=off silently disabling the floor, disk-full behavior, pg_rewind overhead, and a long-standing bug where the enforced minimum is checked only at postmaster start. It closes with practical sizing guidance: set min_wal_size equal to max_wal_size when disk was provisioned for that ceiling.

Source: https://postgr.es/p/9wX. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.