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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@2ndquadrant.com>
This commit is contained in:
Tom Lane 2016-11-25 18:36:10 -05:00
parent ab77a5a456
commit dbdfd114f3
7 changed files with 66 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
doc/src/sgml/config.sgml
View File

@ -1903,10 +1903,10 @@ include_dir 'conf.d'
<xref linkend="guc-shared-buffers">, but smaller than the OS's page
cache, where performance might degrade. This setting may have no
effect on some platforms. The valid range is between
<literal>0</literal>, which disables controlled writeback, and
<literal>0</literal>, which disables forced writeback, and
<literal>2MB</literal>. The default is <literal>512kB</> on Linux,
<literal>0</> elsewhere. (Non-default values of
<symbol>BLCKSZ</symbol> change the default and maximum.)
<literal>0</> elsewhere. (If <symbol>BLCKSZ</symbol> is not 8kB,
the default and maximum values scale proportionally to it.)
This parameter can only be set in the <filename>postgresql.conf</>
file or on the server command line.
</para>
@ -2055,10 +2055,10 @@ include_dir 'conf.d'
that are bigger than <xref linkend="guc-shared-buffers">, but smaller
than the OS's page cache, where performance might degrade. This
setting may have no effect on some platforms. The valid range is
between <literal>0</literal>, which disables controlled writeback,
and <literal>2MB</literal>. The default is <literal>0</> (i.e. no
flush control). (Non-default values of <symbol>BLCKSZ</symbol>
change the maximum.)
between <literal>0</literal>, which disables forced writeback,
and <literal>2MB</literal>. The default is <literal>0</>, i.e., no
forced writeback. (If <symbol>BLCKSZ</symbol> is not 8kB,
the maximum value scales proportionally to it.)
</para>
</listitem>
</varlistentry>
@ -2518,10 +2518,11 @@ include_dir 'conf.d'
<para>
Specifies how often the WAL writer flushes WAL. After flushing WAL it
sleeps for <varname>wal_writer_delay</> milliseconds, unless woken up
by an asynchronously committing transaction. In case the last flush
by an asynchronously committing transaction. If the last flush
happened less than <varname>wal_writer_delay</> milliseconds ago and
less than <varname>wal_writer_flush_after</> bytes of WAL have been
produced since, WAL is only written to the OS, not flushed to disk.
produced since, then WAL is only written to the operating system, not
flushed to disk.
The default value is 200 milliseconds (<literal>200ms</>). Note that
on many systems, the effective resolution of sleep delays is 10
milliseconds; setting <varname>wal_writer_delay</> to a value that is
@ -2540,12 +2541,12 @@ include_dir 'conf.d'
</term>
<listitem>
<para>
Specifies how often the WAL writer flushes WAL. In case the last flush
Specifies how often the WAL writer flushes WAL. If the last flush
happened less than <varname>wal_writer_delay</> milliseconds ago and
less than <varname>wal_writer_flush_after</> bytes of WAL have been
produced since, WAL is only written to the OS, not flushed to disk.
If <varname>wal_writer_flush_after</> is set to <literal>0</> WAL is
flushed every time the WAL writer has written WAL. The default is
produced since, then WAL is only written to the operating system, not
flushed to disk. If <varname>wal_writer_flush_after</> is set
to <literal>0</> then WAL data is flushed immediately. The default is
<literal>1MB</literal>. This parameter can only be set in the
<filename>postgresql.conf</> file or on the server command line.
</para>
@ -2665,10 +2666,10 @@ include_dir 'conf.d'
that are bigger than <xref linkend="guc-shared-buffers">, but smaller
than the OS's page cache, where performance might degrade. This
setting may have no effect on some platforms. The valid range is
between <literal>0</literal>, which disables controlled writeback,
between <literal>0</literal>, which disables forced writeback,
and <literal>2MB</literal>. The default is <literal>256kB</> on
Linux, <literal>0</> elsewhere. (Non-default values of
<symbol>BLCKSZ</symbol> change the default and maximum.)
Linux, <literal>0</> elsewhere. (If <symbol>BLCKSZ</symbol> is not
8kB, the default and maximum values scale proportionally to it.)
This parameter can only be set in the <filename>postgresql.conf</>
file or on the server command line.
</para>

2
src/backend/access/transam/xlog.c
View File

@ -2759,7 +2759,7 @@ XLogFlush(XLogRecPtr record)
* This routine is invoked periodically by the background walwriter process.
*
* Returns TRUE if there was any work to do, even if we skipped flushing due
* to wal_writer_delay/wal_flush_after.
* to wal_writer_delay/wal_writer_flush_after.
*/
bool
XLogBackgroundFlush(void)

8
src/backend/utils/misc/guc.c
View File

@ -2281,7 +2281,6 @@ static struct config_int ConfigureNamesInt[] =
GUC_UNIT_BLOCKS
},
&checkpoint_flush_after,
/* see bufmgr.h: OS dependent default */
DEFAULT_CHECKPOINT_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
NULL, NULL, NULL
},
@ -2310,12 +2309,12 @@ static struct config_int ConfigureNamesInt[] =
{
{"wal_writer_flush_after", PGC_SIGHUP, WAL_SETTINGS,
gettext_noop("Amount of WAL written out by WAL writer triggering a flush."),
gettext_noop("Amount of WAL written out by WAL writer that triggers a flush."),
NULL,
GUC_UNIT_XBLOCKS
},
&WalWriterFlushAfter,
128, 0, INT_MAX,
(1024*1024) / XLOG_BLCKSZ, 0, INT_MAX,
NULL, NULL, NULL
},
@ -2439,7 +2438,6 @@ static struct config_int ConfigureNamesInt[] =
GUC_UNIT_BLOCKS
},
&bgwriter_flush_after,
/* see bufmgr.h: OS dependent default */
DEFAULT_BGWRITER_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
NULL, NULL, NULL
},
@ -2467,7 +2465,7 @@ static struct config_int ConfigureNamesInt[] =
GUC_UNIT_BLOCKS
},
&backend_flush_after,
0, 0, WRITEBACK_MAX_PENDING_FLUSHES,
DEFAULT_BACKEND_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
NULL, NULL, NULL
},

10
src/backend/utils/misc/postgresql.conf.sample
View File

@ -156,8 +156,7 @@
#bgwriter_delay = 200ms # 10-10000ms between rounds
#bgwriter_lru_maxpages = 100 # 0-1000 max buffers written/round
#bgwriter_lru_multiplier = 2.0 # 0-10.0 multiplier on buffers scanned/round
#bgwriter_flush_after = 0 # 0 disables,
# default is 512kB on linux, 0 otherwise
#bgwriter_flush_after = 0 # measured in pages, 0 disables
# - Asynchronous Behavior -
@ -166,7 +165,7 @@
#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 0
#backend_flush_after = 0 # measured in pages, 0 disables
#------------------------------------------------------------------------------
@ -196,7 +195,7 @@
#wal_buffers = -1 # min 32kB, -1 sets based on shared_buffers
# (change requires restart)
#wal_writer_delay = 200ms # 1-10000 milliseconds
#wal_writer_flush_after = 1MB # 0 disables
#wal_writer_flush_after = 1MB # measured in pages, 0 disables
#commit_delay = 0 # range 0-100000, in microseconds
#commit_siblings = 5 # range 1-1000
@ -207,8 +206,7 @@
#max_wal_size = 1GB
#min_wal_size = 80MB
#checkpoint_completion_target = 0.5 # checkpoint target duration, 0.0 - 1.0
#checkpoint_flush_after = 0 # 0 disables,
# default is 256kB on linux, 0 otherwise
#checkpoint_flush_after = 0 # measured in pages, 0 disables
#checkpoint_warning = 30s # 0 disables
# - Archiving -

25
src/bin/initdb/initdb.c
View File

@ -64,11 +64,11 @@
#include "common/file_utils.h"
#include "common/restricted_token.h"
#include "common/username.h"
#include "mb/pg_wchar.h"
#include "fe_utils/string_utils.h"
#include "getaddrinfo.h"
#include "getopt_long.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "fe_utils/string_utils.h"
/* Ideally this would be in a .h file, but it hardly seems worth the trouble */
@ -1095,6 +1095,27 @@ setup_config(void)
conflines = replace_token(conflines, "#dynamic_shared_memory_type = posix",
repltok);
#if DEFAULT_BACKEND_FLUSH_AFTER > 0
snprintf(repltok, sizeof(repltok), "#backend_flush_after = %dkB",
DEFAULT_BACKEND_FLUSH_AFTER * (BLCKSZ / 1024));
conflines = replace_token(conflines, "#backend_flush_after = 0",
repltok);
#endif
#if DEFAULT_BGWRITER_FLUSH_AFTER > 0
snprintf(repltok, sizeof(repltok), "#bgwriter_flush_after = %dkB",
DEFAULT_BGWRITER_FLUSH_AFTER * (BLCKSZ / 1024));
conflines = replace_token(conflines, "#bgwriter_flush_after = 0",
repltok);
#endif
#if DEFAULT_CHECKPOINT_FLUSH_AFTER > 0
snprintf(repltok, sizeof(repltok), "#checkpoint_flush_after = %dkB",
DEFAULT_CHECKPOINT_FLUSH_AFTER * (BLCKSZ / 1024));
conflines = replace_token(conflines, "#checkpoint_flush_after = 0",
repltok);
#endif
#ifndef USE_PREFETCH
conflines = replace_token(conflines,
"#effective_io_concurrency = 1",

18
src/include/pg_config_manual.h
View File

@ -147,6 +147,24 @@
#define USE_PREFETCH
#endif
/*
* Default and maximum values for backend_flush_after, bgwriter_flush_after
* and checkpoint_flush_after; measured in blocks. Currently, these are
* enabled by default if sync_file_range() exists, ie, only on Linux. Perhaps
* we could also enable by default if we have mmap and msync(MS_ASYNC)?
*/
#ifdef HAVE_SYNC_FILE_RANGE
#define DEFAULT_BACKEND_FLUSH_AFTER 0 /* never enabled by default */
#define DEFAULT_BGWRITER_FLUSH_AFTER 64
#define DEFAULT_CHECKPOINT_FLUSH_AFTER 32
#else
#define DEFAULT_BACKEND_FLUSH_AFTER 0
#define DEFAULT_BGWRITER_FLUSH_AFTER 0
#define DEFAULT_CHECKPOINT_FLUSH_AFTER 0
#endif
/* upper limit for all three variables */
#define WRITEBACK_MAX_PENDING_FLUSHES 256
/*
* USE_SSL code should be compiled only when compiling with an SSL
* implementation. (Currently, only OpenSSL is supported, but we might add

11
src/include/storage/bufmgr.h
View File

@ -54,17 +54,6 @@ struct WritebackContext;
extern PGDLLIMPORT int NBuffers;
/* in bufmgr.c */
#define WRITEBACK_MAX_PENDING_FLUSHES 256
/* FIXME: Also default to on for mmap && msync(MS_ASYNC)? */
#ifdef HAVE_SYNC_FILE_RANGE
#define DEFAULT_CHECKPOINT_FLUSH_AFTER 32
#define DEFAULT_BGWRITER_FLUSH_AFTER 64
#else
#define DEFAULT_CHECKPOINT_FLUSH_AFTER 0
#define DEFAULT_BGWRITER_FLUSH_AFTER 0
#endif /* HAVE_SYNC_FILE_RANGE */
extern bool zero_damaged_pages;
extern int bgwriter_lru_maxpages;
extern double bgwriter_lru_multiplier;