From 8607189eb19302c509eed78a7a2db55b9a2d70b3 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Sat, 31 May 2025 22:50:22 +1200 Subject: [PATCH 1/2] Add io_min_fallocate setting. BTRFS's compression is reported to be disabled by posix_fallocate(), so offer a way to turn it off. The previous coding had a threshold of 8 blocks before using that instead of writing zeroes, so make that configurable. 0 means never, and other numbers specify a threshold in blocks, defaulting to 8 as before. Reported-by: Dimitrios Apostolou Discussion: https://postgr.es/m/b1843124-fd22-e279-a31f-252dffb6fbf2%40gmx.net --- doc/src/sgml/config.sgml | 17 +++++++++++++++++ src/backend/storage/file/fd.c | 3 +++ src/backend/storage/smgr/md.c | 6 ++---- src/backend/utils/misc/guc_tables.c | 12 ++++++++++++ src/backend/utils/misc/postgresql.conf.sample | 1 + src/include/storage/fd.h | 1 + 6 files changed, 36 insertions(+), 4 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index f4a0191c55b..7d476665f42 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2684,6 +2684,23 @@ include_dir 'conf.d' + + io_min_fallocate (integer) + + io_min_fallocate configuration parameter + + + + + Threshold at which posix_fallocate() is used to + extend data files instead of writing zeroes. 0 + means never (always write + zeroes), and other values indicate a number of blocks. + The default is 8. + + + + io_max_combine_limit (integer) diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c index 0e8299dd556..ff16b5cc6bd 100644 --- a/src/backend/storage/file/fd.c +++ b/src/backend/storage/file/fd.c @@ -164,6 +164,9 @@ bool data_sync_retry = false; /* How SyncDataDirectory() should do its job. */ int recovery_init_sync_method = DATA_DIR_SYNC_METHOD_FSYNC; +/* At what size FileFallocate() should be preferred over FileZero(). */ +int io_min_fallocate = 8; + /* Which kinds of files should be opened with PG_O_DIRECT. */ int io_direct_flags; diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c index 2ccb0faceb5..6d1b9cb65b2 100644 --- a/src/backend/storage/smgr/md.c +++ b/src/backend/storage/smgr/md.c @@ -588,11 +588,9 @@ mdzeroextend(SMgrRelation reln, ForkNumber forknum, * to allocate page cache space for the extended pages. * * However, we don't use FileFallocate() for small extensions, as it - * defeats delayed allocation on some filesystems. Not clear where - * that decision should be made though? For now just use a cutoff of - * 8, anything between 4 and 8 worked OK in some local testing. + * defeats delayed allocation on some filesystems. */ - if (numblocks > 8) + if (io_min_fallocate > 0 && numblocks >= io_min_fallocate) { int ret; diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c index 2f8cbd86759..a75ff8623d9 100644 --- a/src/backend/utils/misc/guc_tables.c +++ b/src/backend/utils/misc/guc_tables.c @@ -3265,6 +3265,18 @@ struct config_int ConfigureNamesInt[] = NULL }, + { + {"io_min_fallocate", + PGC_USERSET, + RESOURCES_IO, + gettext_noop("Threshold for preferring posix_fallocate() when extending data files."), + NULL, + GUC_UNIT_BLOCKS + }, + &io_min_fallocate, + 8, 0, INT_MAX + }, + { {"io_max_combine_limit", PGC_POSTMASTER, diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample index 87ce76b18f4..8b712ef244f 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -200,6 +200,7 @@ #backend_flush_after = 0 # measured in pages, 0 disables #effective_io_concurrency = 16 # 1-1000; 0 disables issuing multiple simultaneous IO requests #maintenance_io_concurrency = 16 # 1-1000; same as effective_io_concurrency +#io_min_fallocate = 8 # min size at which to prefer posix_fallocate, 0 = never #io_max_combine_limit = 128kB # usually 1-128 blocks (depends on OS) # (change requires restart) #io_combine_limit = 128kB # usually 1-128 blocks (depends on OS) diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h index b77d8e5e30e..b8714e5ceb8 100644 --- a/src/include/storage/fd.h +++ b/src/include/storage/fd.h @@ -60,6 +60,7 @@ typedef int File; extern PGDLLIMPORT int max_files_per_process; extern PGDLLIMPORT bool data_sync_retry; extern PGDLLIMPORT int recovery_init_sync_method; +extern PGDLLIMPORT int io_min_fallocate; extern PGDLLIMPORT int io_direct_flags; /* -- 2.39.5