pg_prefaulter is used to mitigate the effects of PostgreSQL replication lag.
https://github.com/joyent/pg_prefaulter If you’ve seen replication lag due to pg_repack, VACUUM, or a write-heavy workload, the pg_prefaulter reduces the apply lag on followers. In a primary-follower cluster using PostgreSQL streaming replication, the PostgreSQL’s primary database instance enjoys the benefit of being able to parallelize its random IO workload. The follower, however, is not so fortunate. The follower receives a sequential stream of WAL records and sequentially schedules all pread(2) IOs in order in a single process with blocking IO. If the average IO latency per random pread(2) is ~8ms, that means that the follower can only complete ~125 random IO pread(2) calls per second (i.e. only 125 WAL records/second). The pg_prefaulter reads the stream of WAL records using pg_xlogdump(1) and schedules concurrent IOs in order to prefault PostgreSQL heap pages into the follower’s filesystem cache. The effect of this is dramatic in that the follower is able to apply pages with a filesystem cache-hit. pg_prefaulter can also pull the WAL files from process arguments when a connection is not available, this allows pg_prefaulter to accelerate the recovery and startup time of PostgreSQL. If you’ve ever sat twiddling your thumbs waiting for the database to start up, pg_prefaulter should improve the startup time of PostgreSQL. Intro: https://github.com/joyent/pg_prefaulter#pg_prefaulter Background: https://github.com/joyent/pg_prefaulter#background Cheers. -sc -- Sean Chittenden
signature.asc
Description: PGP signature
