Open source software developer focusing on PostgreSQL at Microsoft. Committer on the PostgreSQL and FreeBSD projects. Interested in open hardware, software, protocols, and standards. Speaker at conferences including PGCon, PGDU, FOSDEM, & Citus Con: An Event for Postgres.
Written byBy Thomas Munro | November 10, 2022Nov 10, 2022
Reducing replication lag with IO concurrency in Postgres 15
PostgreSQL 15 improves crash recovery and physical replication performance of some large and very busy databases by trying to minimise I/O stalls. A standby server might now have an easier time keeping up with the primary.
How? The change in PostgreSQL15 is that recovery now uses the maintenance_io_concurrency setting (default is 10, but you can increase it) to decide how many concurrent I/Os to try to initiate, rather than doing random read I/Os one at a time. With big and busy databases, when I/O concurrency increases, replication lag can be reduced.
Written byBy Thomas Munro | December 12, 2020Dec 12, 2020
[UPDATE in Sep 2021]: This blog post was originally written during the PostgreSQL 14 development cycle. The feature discussed is now a candidate for PostgreSQL 15 and the text has been updated to reflect this.
As part of my work on the open source PostgreSQL team at Microsoft, I've been developing a new feature for PostgreSQL to track dependencies on collation versions, with help from co-author Julien Rouhaud and many others who have contributed ideas. It's taken a long time to build a consensus on how to tackle this thorny problem (work I began at EnterpriseDB and continued at Microsoft), and you can read about some of the details and considerations in the commit message below and the referenced discussion thread. We're not quite done with that yet. It was originally planned for PostgreSQL 14, but some unhandled complications arose so this project is back in the workshop.
Author: Thomas Munro <email@example.com>
Date: Mon Nov 2 19:50:45 2020 +1300
Track collation versions for indexes.
Record the current version of dependent collations in pg_depend when
creating or rebuilding an index. When accessing the index later, warn
that the index may be corrupted if the current version doesn't match.
Thanks to Douglas Doole, Peter Eisentraut, Christoph Berg, Laurenz Albe,
Michael Paquier, Robert Haas, Tom Lane and others for very helpful
Author: Thomas Munro <firstname.lastname@example.org>
Author: Julien Rouhaud <email@example.com>
Reviewed-by: Peter Eisentraut <firstname.lastname@example.org> (earlier versions)
In this article I'll talk about the problem we need to solve—that PostgreSQL indexes can get corrupted by changes in collations that occur naturally over time—and how the new feature will make things better in a future version of PostgreSQL. Plus, you’ll get a bit of background on collations, too.