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>
<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>
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>
<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
</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>
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>
* 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)
GUC_UNIT_BLOCKS
},
&checkpoint_flush_after,
- /* see bufmgr.h: OS dependent default */
DEFAULT_CHECKPOINT_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
NULL, NULL, NULL
},
{
{"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
},
GUC_UNIT_BLOCKS
},
&bgwriter_flush_after,
- /* see bufmgr.h: OS dependent default */
DEFAULT_BGWRITER_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
NULL, NULL, NULL
},
GUC_UNIT_BLOCKS
},
&backend_flush_after,
- 0, 0, WRITEBACK_MAX_PENDING_FLUSHES,
+ DEFAULT_BACKEND_FLUSH_AFTER, 0, WRITEBACK_MAX_PENDING_FLUSHES,
NULL, NULL, NULL
},
#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 -
#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
#------------------------------------------------------------------------------
#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
#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 -
#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 */
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",
#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
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;
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