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
Branch
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master
Details
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http://git.postgresql.org/pg/commitdiff/4bc0f165cb4fbd660648c0153485b3d6f55d80ea
Modified Files
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doc/src/sgml/config.sgml | 6 +++---
src/backend/utils/misc/guc.c | 3 +--
src/backend/utils/misc/postgresql.conf.sample | 3 +--
src/include/storage/bufmgr.h | 2 --
4 files changed, 5 insertions(+), 9 deletions(-)