pgsql: Bring some clarity to the defaults for the xxx_flush_after param

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: pgsql-committers(at)postgresql(dot)org
Subject: pgsql: Bring some clarity to the defaults for the xxx_flush_after param
Date: 2016-11-25 23:36:26
Message-ID: E1cAQ2c-0005vF-8C@gemulon.postgresql.org
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Bring some clarity to the defaults for the xxx_flush_after parameters.

Instead of confusingly stating platform-dependent defaults for these
parameters in the comments in postgresql.conf.sample (with the main
entry being a lie on Linux), teach initdb to install the correct
platform-dependent value in postgresql.conf, similarly to the way
we handle other platform-dependent defaults. This won't do anything
for existing 9.6 installations, but since it's effectively only a
documentation improvement, that seems OK.

Since this requires initdb to have access to the default values,
move the #define's for those to pg_config_manual.h; the original
placement in bufmgr.h is unworkable because that file can't be
included by frontend programs.

Adjust the default value for wal_writer_flush_after so that it is 1MB
regardless of XLOG_BLCKSZ, conforming to what is stated in both the
SGML docs and postgresql.conf. (We could alternatively make it scale
with XLOG_BLCKSZ, but I'm not sure I see the point.)

Copy-edit related SGML documentation.

Fabien Coelho and Tom Lane, per a gripe from Tomas Vondra.

Discussion: <30ebc6e3-8358-09cf-44a8-578252938424(at)2ndquadrant(dot)com>

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/dbdfd114f34443f1e4ad16ce2721f9817d3b3d80

Modified Files
--------------
doc/src/sgml/config.sgml | 33 ++++++++++++++-------------
src/backend/access/transam/xlog.c | 2 +-
src/backend/utils/misc/guc.c | 8 +++----
src/backend/utils/misc/postgresql.conf.sample | 10 ++++----
src/bin/initdb/initdb.c | 25 ++++++++++++++++++--
src/include/pg_config_manual.h | 18 +++++++++++++++
src/include/storage/bufmgr.h | 11 ---------
7 files changed, 66 insertions(+), 41 deletions(-)

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