From 4830f102432518d06b50f61e0ab4c0c07082617b Mon Sep 17 00:00:00 2001 From: David Rowley Date: Mon, 3 Apr 2023 23:05:58 +1200 Subject: [PATCH] Disable vacuum's use of a buffer access strategy during failsafe Traditionally, vacuum always makes use of a buffer access strategy 32 buffers in size. This means that running vacuums tend not to cause too many shared buffers to become dirty, however, this can cause vacuums to run much more slowly than they otherwise could as WAL flushes will occur more frequently due to having to flush WAL out to the LSN of the dirty page before that page can be written to disk. When we are performing failsafe VACUUMs (as added in 1e55e7d17), we really want to make the vacuum work go as quickly as possible, so here we disable the buffer access strategy when entering failsafe mode while vacuuming a relation. Per idea and analyis from Andres Freund. In passing, also include some changes I had intended for 32fbe0239. Author: Melanie Plageman Reviewed-by: Justin Pryzby, David Rowley Discussion: https://postgr.es/m/20230111182720.ejifsclfwymw2reb%40awork3.anarazel.de --- doc/src/sgml/config.sgml | 8 ++++++-- src/backend/access/heap/vacuumlazy.c | 7 +++++++ src/backend/commands/vacuum.c | 8 +++++--- 3 files changed, 18 insertions(+), 5 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index fcb53c6997..5bad13d24a 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -9320,8 +9320,12 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv; When the failsafe is triggered, any cost-based delay that is - in effect will no longer be applied, and further non-essential - maintenance tasks (such as index vacuuming) are bypassed. + in effect will no longer be applied, further non-essential + maintenance tasks (such as index vacuuming) are bypassed, and any + Buffer Access Strategy + in use will be disabled resulting in VACUUM being + free to make use of all of + shared buffers. The default is 1.6 billion transactions. Although users can diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index ae628d747d..3e5d3982c7 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -2623,6 +2623,13 @@ lazy_check_wraparound_failsafe(LVRelState *vacrel) { vacrel->failsafe_active = true; + /* + * Abandon use of a buffer access strategy to allow use of all of + * shared buffers. We assume the caller who allocated the memory for + * the BufferAccessStrategy will free it. + */ + vacrel->bstrategy = NULL; + /* Disable index vacuuming, index cleanup, and heap rel truncation */ vacrel->do_index_vacuuming = false; vacrel->do_index_cleanup = false; diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index 1c3437336d..da85330ef4 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -391,11 +391,13 @@ vacuum(List *relations, VacuumParams *params, /* * If caller didn't give us a buffer strategy object, make one in the - * cross-transaction memory context. + * cross-transaction memory context. We needn't bother making this for + * VACUUM (FULL) or VACUUM (ONLY_DATABASE_STATS) as they'll not make use + * of it. */ if (bstrategy == NULL && - !(params->options & VACOPT_ONLY_DATABASE_STATS || - params->options & VACOPT_FULL)) + (params->options & (VACOPT_ONLY_DATABASE_STATS | + VACOPT_FULL)) == 0) { MemoryContext old_context = MemoryContextSwitchTo(vac_context);