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Commit255bcd2

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Bring some clarity to the defaults for the xxx_flush_after parameters.
Instead of confusingly stating platform-dependent defaults for theseparameters in the comments in postgresql.conf.sample (with the mainentry being a lie on Linux), teach initdb to install the correctplatform-dependent value in postgresql.conf, similarly to the waywe handle other platform-dependent defaults. This won't do anythingfor existing 9.6 installations, but since it's effectively only adocumentation 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 originalplacement in bufmgr.h is unworkable because that file can't beincluded by frontend programs.Adjust the default value for wal_writer_flush_after so that it is 1MBregardless of XLOG_BLCKSZ, conforming to what is stated in both theSGML docs and postgresql.conf. (We could alternatively make it scalewith 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>
1 parent474de76 commit255bcd2

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7 files changed

+65
-40
lines changed

7 files changed

+65
-40
lines changed

‎doc/src/sgml/config.sgml‎

Lines changed: 17 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -1902,10 +1902,10 @@ include_dir 'conf.d'
19021902
<xref linkend="guc-shared-buffers">, but smaller than the OS's page
19031903
cache, where performance might degrade. This setting may have no
19041904
effect on some platforms. The valid range is between
1905-
<literal>0</literal>, which disablescontrolled writeback, and
1905+
<literal>0</literal>, which disablesforced writeback, and
19061906
<literal>2MB</literal>. The default is <literal>512kB</> on Linux,
1907-
<literal>0</> elsewhere. (Non-default values of
1908-
<symbol>BLCKSZ</symbol> changethe default and maximum.)
1907+
<literal>0</> elsewhere. (If <symbol>BLCKSZ</symbol> is not 8kB,
1908+
the default and maximum values scale proportionally to it.)
19091909
This parameter can only be set in the <filename>postgresql.conf</>
19101910
file or on the server command line.
19111911
</para>
@@ -2054,10 +2054,10 @@ include_dir 'conf.d'
20542054
that are bigger than <xref linkend="guc-shared-buffers">, but smaller
20552055
than the OS's page cache, where performance might degrade. This
20562056
setting may have no effect on some platforms. The valid range is
2057-
between <literal>0</literal>, which disablescontrolled writeback,
2058-
and <literal>2MB</literal>. The default is <literal>0</> (i.e. no
2059-
flush control). (Non-default values of<symbol>BLCKSZ</symbol>
2060-
changethe maximum.)
2057+
between <literal>0</literal>, which disablesforced writeback,
2058+
and <literal>2MB</literal>. The default is <literal>0</>,i.e., no
2059+
forced writeback. (If<symbol>BLCKSZ</symbol> is not 8kB,
2060+
the maximum value scales proportionally to it.)
20612061
</para>
20622062
</listitem>
20632063
</varlistentry>
@@ -2517,10 +2517,11 @@ include_dir 'conf.d'
25172517
<para>
25182518
Specifies how often the WAL writer flushes WAL. After flushing WAL it
25192519
sleeps for <varname>wal_writer_delay</> milliseconds, unless woken up
2520-
by an asynchronously committing transaction.In case the last flush
2520+
by an asynchronously committing transaction.If the last flush
25212521
happened less than <varname>wal_writer_delay</> milliseconds ago and
25222522
less than <varname>wal_writer_flush_after</> bytes of WAL have been
2523-
produced since, WAL is only written to the OS, not flushed to disk.
2523+
produced since, then WAL is only written to the operating system, not
2524+
flushed to disk.
25242525
The default value is 200 milliseconds (<literal>200ms</>). Note that
25252526
on many systems, the effective resolution of sleep delays is 10
25262527
milliseconds; setting <varname>wal_writer_delay</> to a value that is
@@ -2539,12 +2540,12 @@ include_dir 'conf.d'
25392540
</term>
25402541
<listitem>
25412542
<para>
2542-
Specifies how often the WAL writer flushes WAL.In case the last flush
2543+
Specifies how often the WAL writer flushes WAL.If the last flush
25432544
happened less than <varname>wal_writer_delay</> milliseconds ago and
25442545
less than <varname>wal_writer_flush_after</> bytes of WAL have been
2545-
produced since, WAL is only written to theOS, not flushed to disk.
2546-
If <varname>wal_writer_flush_after</> is set to <literal>0</> WAL is
2547-
flushed every time theWALwriter has written WAL. The default is
2546+
produced since,thenWAL is only written to theoperating system, not
2547+
flushed to disk.If <varname>wal_writer_flush_after</> is set
2548+
to <literal>0</> thenWALdata is flushed immediately. The default is
25482549
<literal>1MB</literal>. This parameter can only be set in the
25492550
<filename>postgresql.conf</> file or on the server command line.
25502551
</para>
@@ -2664,10 +2665,10 @@ include_dir 'conf.d'
26642665
that are bigger than <xref linkend="guc-shared-buffers">, but smaller
26652666
than the OS's page cache, where performance might degrade. This
26662667
setting may have no effect on some platforms. The valid range is
2667-
between <literal>0</literal>, which disablescontrolled writeback,
2668+
between <literal>0</literal>, which disablesforced writeback,
26682669
and <literal>2MB</literal>. The default is <literal>256kB</> on
2669-
Linux, <literal>0</> elsewhere. (Non-default values of
2670-
<symbol>BLCKSZ</symbol> changethe default and maximum.)
2670+
Linux, <literal>0</> elsewhere. (If <symbol>BLCKSZ</symbol> is not
2671+
8kB,the default and maximum values scale proportionally to it.)
26712672
This parameter can only be set in the <filename>postgresql.conf</>
26722673
file or on the server command line.
26732674
</para>

‎src/backend/access/transam/xlog.c‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2755,7 +2755,7 @@ XLogFlush(XLogRecPtr record)
27552755
* This routine is invoked periodically by the background walwriter process.
27562756
*
27572757
* Returns TRUE if there was any work to do, even if we skipped flushing due
2758-
* to wal_writer_delay/wal_flush_after.
2758+
* to wal_writer_delay/wal_writer_flush_after.
27592759
*/
27602760
bool
27612761
XLogBackgroundFlush(void)

‎src/backend/utils/misc/guc.c‎

Lines changed: 3 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -2275,7 +2275,6 @@ static struct config_int ConfigureNamesInt[] =
22752275
GUC_UNIT_BLOCKS
22762276
},
22772277
&checkpoint_flush_after,
2278-
/* see bufmgr.h: OS dependent default */
22792278
DEFAULT_CHECKPOINT_FLUSH_AFTER,0,WRITEBACK_MAX_PENDING_FLUSHES,
22802279
NULL,NULL,NULL
22812280
},
@@ -2304,12 +2303,12 @@ static struct config_int ConfigureNamesInt[] =
23042303

23052304
{
23062305
{"wal_writer_flush_after",PGC_SIGHUP,WAL_SETTINGS,
2307-
gettext_noop("Amount of WAL written out by WAL writertriggering a flush."),
2306+
gettext_noop("Amount of WAL written out by WAL writerthat triggers a flush."),
23082307
NULL,
23092308
GUC_UNIT_XBLOCKS
23102309
},
23112310
&WalWriterFlushAfter,
2312-
128,0,INT_MAX,
2311+
(1024*1024) /XLOG_BLCKSZ,0,INT_MAX,
23132312
NULL,NULL,NULL
23142313
},
23152314

@@ -2433,7 +2432,6 @@ static struct config_int ConfigureNamesInt[] =
24332432
GUC_UNIT_BLOCKS
24342433
},
24352434
&bgwriter_flush_after,
2436-
/* see bufmgr.h: OS dependent default */
24372435
DEFAULT_BGWRITER_FLUSH_AFTER,0,WRITEBACK_MAX_PENDING_FLUSHES,
24382436
NULL,NULL,NULL
24392437
},
@@ -2461,7 +2459,7 @@ static struct config_int ConfigureNamesInt[] =
24612459
GUC_UNIT_BLOCKS
24622460
},
24632461
&backend_flush_after,
2464-
0,0,WRITEBACK_MAX_PENDING_FLUSHES,
2462+
DEFAULT_BACKEND_FLUSH_AFTER,0,WRITEBACK_MAX_PENDING_FLUSHES,
24652463
NULL,NULL,NULL
24662464
},
24672465

‎src/backend/utils/misc/postgresql.conf.sample‎

Lines changed: 5 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -156,17 +156,16 @@
156156
#bgwriter_delay = 200ms# 10-10000ms between rounds
157157
#bgwriter_lru_maxpages = 100# 0-1000 max buffers written/round
158158
#bgwriter_lru_multiplier = 2.0# 0-10.0 multiplier on buffers scanned/round
159-
#bgwriter_flush_after = 0# 0 disables,
160-
# default is 512kB on linux, 0 otherwise
159+
#bgwriter_flush_after = 0# measured in pages, 0 disables
161160

162161
# - Asynchronous Behavior -
163162

164163
#effective_io_concurrency = 1# 1-1000; 0 disables prefetching
165164
#max_worker_processes = 8# (change requires restart)
166165
#max_parallel_workers_per_gather = 0# taken from max_worker_processes
167166
#old_snapshot_threshold = -1# 1min-60d; -1 disables; 0 is immediate
168-
# (change requires restart)
169-
#backend_flush_after = 0#0 disables, default is 0
167+
# (change requires restart)
168+
#backend_flush_after = 0#measured in pages, 0 disables
170169

171170

172171
#------------------------------------------------------------------------------
@@ -196,7 +195,7 @@
196195
#wal_buffers = -1# min 32kB, -1 sets based on shared_buffers
197196
# (change requires restart)
198197
#wal_writer_delay = 200ms# 1-10000 milliseconds
199-
#wal_writer_flush_after = 1MB# 0 disables
198+
#wal_writer_flush_after = 1MB#measured in pages,0 disables
200199

201200
#commit_delay = 0# range 0-100000, in microseconds
202201
#commit_siblings = 5# range 1-1000
@@ -207,8 +206,7 @@
207206
#max_wal_size = 1GB
208207
#min_wal_size = 80MB
209208
#checkpoint_completion_target = 0.5# checkpoint target duration, 0.0 - 1.0
210-
#checkpoint_flush_after = 0# 0 disables,
211-
# default is 256kB on linux, 0 otherwise
209+
#checkpoint_flush_after = 0# measured in pages, 0 disables
212210
#checkpoint_warning = 30s# 0 disables
213211

214212
# - Archiving -

‎src/bin/initdb/initdb.c‎

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1287,6 +1287,27 @@ setup_config(void)
12871287
conflines=replace_token(conflines,"#dynamic_shared_memory_type = posix",
12881288
repltok);
12891289

1290+
#ifDEFAULT_BACKEND_FLUSH_AFTER>0
1291+
snprintf(repltok,sizeof(repltok),"#backend_flush_after = %dkB",
1292+
DEFAULT_BACKEND_FLUSH_AFTER* (BLCKSZ /1024));
1293+
conflines=replace_token(conflines,"#backend_flush_after = 0",
1294+
repltok);
1295+
#endif
1296+
1297+
#ifDEFAULT_BGWRITER_FLUSH_AFTER>0
1298+
snprintf(repltok,sizeof(repltok),"#bgwriter_flush_after = %dkB",
1299+
DEFAULT_BGWRITER_FLUSH_AFTER* (BLCKSZ /1024));
1300+
conflines=replace_token(conflines,"#bgwriter_flush_after = 0",
1301+
repltok);
1302+
#endif
1303+
1304+
#ifDEFAULT_CHECKPOINT_FLUSH_AFTER>0
1305+
snprintf(repltok,sizeof(repltok),"#checkpoint_flush_after = %dkB",
1306+
DEFAULT_CHECKPOINT_FLUSH_AFTER* (BLCKSZ /1024));
1307+
conflines=replace_token(conflines,"#checkpoint_flush_after = 0",
1308+
repltok);
1309+
#endif
1310+
12901311
#ifndefUSE_PREFETCH
12911312
conflines=replace_token(conflines,
12921313
"#effective_io_concurrency = 1",

‎src/include/pg_config_manual.h‎

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -147,6 +147,24 @@
147147
#defineUSE_PREFETCH
148148
#endif
149149

150+
/*
151+
* Default and maximum values for backend_flush_after, bgwriter_flush_after
152+
* and checkpoint_flush_after; measured in blocks. Currently, these are
153+
* enabled by default if sync_file_range() exists, ie, only on Linux. Perhaps
154+
* we could also enable by default if we have mmap and msync(MS_ASYNC)?
155+
*/
156+
#ifdefHAVE_SYNC_FILE_RANGE
157+
#defineDEFAULT_BACKEND_FLUSH_AFTER 0/* never enabled by default */
158+
#defineDEFAULT_BGWRITER_FLUSH_AFTER 64
159+
#defineDEFAULT_CHECKPOINT_FLUSH_AFTER 32
160+
#else
161+
#defineDEFAULT_BACKEND_FLUSH_AFTER 0
162+
#defineDEFAULT_BGWRITER_FLUSH_AFTER 0
163+
#defineDEFAULT_CHECKPOINT_FLUSH_AFTER 0
164+
#endif
165+
/* upper limit for all three variables */
166+
#defineWRITEBACK_MAX_PENDING_FLUSHES 256
167+
150168
/*
151169
* USE_SSL code should be compiled only when compiling with an SSL
152170
* implementation. (Currently, only OpenSSL is supported, but we might add

‎src/include/storage/bufmgr.h‎

Lines changed: 0 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -54,17 +54,6 @@ struct WritebackContext;
5454
externPGDLLIMPORTintNBuffers;
5555

5656
/* in bufmgr.c */
57-
#defineWRITEBACK_MAX_PENDING_FLUSHES 256
58-
59-
/* FIXME: Also default to on for mmap && msync(MS_ASYNC)? */
60-
#ifdefHAVE_SYNC_FILE_RANGE
61-
#defineDEFAULT_CHECKPOINT_FLUSH_AFTER 32
62-
#defineDEFAULT_BGWRITER_FLUSH_AFTER 64
63-
#else
64-
#defineDEFAULT_CHECKPOINT_FLUSH_AFTER 0
65-
#defineDEFAULT_BGWRITER_FLUSH_AFTER 0
66-
#endif/* HAVE_SYNC_FILE_RANGE */
67-
6857
externboolzero_damaged_pages;
6958
externintbgwriter_lru_maxpages;
7059
externdoublebgwriter_lru_multiplier;

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