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| author | Andres Freund <andres@anarazel.de> | 2016-06-10 15:31:11 -0700 |
|---|---|---|
| committer | Andres Freund <andres@anarazel.de> | 2016-06-10 15:31:11 -0700 |
| commit | 4bc0f165cb4fbd660648c0153485b3d6f55d80ea (patch) | |
| tree | fde5dfaf4d50a935d67ce57e0eb299601ff104ed /src | |
| parent | 3303ea1a327b41d3b406d7be7a5ce2901e561066 (diff) | |
| download | postgresql-4bc0f165cb4fbd660648c0153485b3d6f55d80ea.tar.gz postgresql-4bc0f165cb4fbd660648c0153485b3d6f55d80ea.zip | |
Change default of backend_flush_after GUC to 0 (disabled).
While beneficial, both for throughput and average/worst case latency, in
a significant number of workloads, there are other workloads in which
backend_flush_after can cause significant performance regressions in
comparison to < 9.6 releases. The regression is most likely when the hot
data set is bigger than shared buffers, but significantly smaller than
the operating system's page cache.
I personally think that the benefit of enabling backend flush control is
considerably bigger than the potential downsides, but a fair argument
can be made that not regressing is more important than improving
performance/latency. As the latter is the consensus, change the default
to 0.
The other settings introduced in 428b1d6b2 do not have the same
potential for regressions, so leave them enabled.
Benchmarks leading up to changing the default have been performed by
Mithun Cy, Ashutosh Sharma and Robert Haas.
Discussion: CAD__OuhPmc6XH=wYRm_+Q657yQE88DakN4=Ybh2oveFasHkoeA@mail.gmail.com
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/utils/misc/guc.c | 3 | ||||
| -rw-r--r-- | src/backend/utils/misc/postgresql.conf.sample | 3 | ||||
| -rw-r--r-- | src/include/storage/bufmgr.h | 2 |
3 files changed, 2 insertions, 6 deletions
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index cf3eb1a4f14..9b02111a834 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -2457,8 +2457,7 @@ static struct config_int ConfigureNamesInt[] = GUC_UNIT_BLOCKS }, &backend_flush_after, - /* see bufmgr.h: OS dependent default */ - DEFAULT_BACKEND_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES, + 0, 0, WRITEBACK_MAX_PENDING_FLUSHES, NULL, NULL, NULL }, diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample index 3ef2a9761cc..8260e371bc9 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -170,8 +170,7 @@ #max_parallel_workers_per_gather = 2 # taken from max_worker_processes #old_snapshot_threshold = -1 # 1min-60d; -1 disables; 0 is immediate # (change requires restart) -#backend_flush_after = 0 # 0 disables, - # default is 128kb on linux, 0 otherwise +#backend_flush_after = 0 # 0 disables, default is 0 #------------------------------------------------------------------------------ diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 38b602724e1..3d5dea7efb5 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -60,11 +60,9 @@ extern PGDLLIMPORT int NBuffers; /* FIXME: Also default to on for mmap && msync(MS_ASYNC)? */ #ifdef HAVE_SYNC_FILE_RANGE #define DEFAULT_CHECKPOINT_FLUSH_AFTER 32 -#define DEFAULT_BACKEND_FLUSH_AFTER 16 #define DEFAULT_BGWRITER_FLUSH_AFTER 64 #else #define DEFAULT_CHECKPOINT_FLUSH_AFTER 0 -#define DEFAULT_BACKEND_FLUSH_AFTER 0 #define DEFAULT_BGWRITER_FLUSH_AFTER 0 #endif /* HAVE_SYNC_FILE_RANGE */ |