On Thu, Sep 09, 2021 at 01:19:14PM +0900, Michael Paquier wrote: > I broke that again, so rebased as v9 attached.
Well. -- Michael
From 09b1f5a5e0e88a6d84bfc2f8a1bc410e21fb3775 Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Thu, 9 Sep 2021 13:10:24 +0900
Subject: [PATCH v9 1/2] Introduce huge_pages_required GUC.
This runtime-computed GUC shows the number of huge pages required
for the server's main shared memory area.
---
src/include/storage/pg_shmem.h | 1 +
src/backend/port/sysv_shmem.c | 16 +++++++++++-----
src/backend/port/win32_shmem.c | 14 ++++++++++++++
src/backend/storage/ipc/ipci.c | 14 ++++++++++++++
src/backend/utils/misc/guc.c | 12 ++++++++++++
doc/src/sgml/config.sgml | 21 +++++++++++++++++++++
6 files changed, 73 insertions(+), 5 deletions(-)
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 059df1b72c..518eb86065 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -87,5 +87,6 @@ extern PGShmemHeader *PGSharedMemoryCreate(Size size,
PGShmemHeader **shim);
extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
extern void PGSharedMemoryDetach(void);
+extern void GetHugePageSize(Size *hugepagesize, int *mmap_flags);
#endif /* PG_SHMEM_H */
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 9de96edf6a..125e2d47ec 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -456,8 +456,6 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
return shmStat.shm_nattch == 0 ? SHMSTATE_UNATTACHED :
SHMSTATE_ATTACHED;
}
-#ifdef MAP_HUGETLB
-
/*
* Identify the huge page size to use, and compute the related mmap flags.
*
@@ -476,11 +474,19 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
* such as increasing shared_buffers to absorb the extra space.
*
* Returns the (real, assumed or config provided) page size into *hugepagesize,
- * and the hugepage-related mmap flags to use into *mmap_flags.
+ * and the hugepage-related mmap flags to use into *mmap_flags. If huge pages
+ * is not supported, *hugepagesize and *mmap_flags will be set to 0.
*/
-static void
+void
GetHugePageSize(Size *hugepagesize, int *mmap_flags)
{
+#ifndef MAP_HUGETLB
+
+ *hugepagesize = 0;
+ *mmap_flags = 0;
+
+#else
+
Size default_hugepagesize = 0;
/*
@@ -553,9 +559,9 @@ GetHugePageSize(Size *hugepagesize, int *mmap_flags)
*mmap_flags |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
}
#endif
-}
#endif /* MAP_HUGETLB */
+}
/*
* Creates an anonymous mmap()ed shared memory segment.
diff --git a/src/backend/port/win32_shmem.c b/src/backend/port/win32_shmem.c
index d7a71992d8..90de2ab4e1 100644
--- a/src/backend/port/win32_shmem.c
+++ b/src/backend/port/win32_shmem.c
@@ -605,3 +605,17 @@ pgwin32_ReserveSharedMemoryRegion(HANDLE hChild)
return true;
}
+
+/*
+ * This function is provided for consistency with sysv_shmem.c and does not
+ * provide any useful information for Windows. To obtain the large page size,
+ * use GetLargePageMinimum() instead.
+ *
+ * This always sets *hugepagesize and *mmap_flags to 0.
+ */
+void
+GetHugePageSize(Size *hugepagesize, int *mmap_flags)
+{
+ *hugepagesize = 0;
+ *mmap_flags = 0;
+}
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 13f3926ff6..91490653cf 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -326,6 +326,9 @@ InitializeShmemGUCs(void)
char buf[64];
Size size_b;
Size size_mb;
+ Size hp_size;
+ Size hp_required;
+ int unused;
/*
* Calculate the shared memory size and round up to the nearest
megabyte.
@@ -334,4 +337,15 @@ InitializeShmemGUCs(void)
size_mb = add_size(size_b, (1024 * 1024) - 1) / (1024 * 1024);
sprintf(buf, "%zu", size_mb);
SetConfigOption("shared_memory_size", buf, PGC_INTERNAL,
PGC_S_OVERRIDE);
+
+ /*
+ * Calculate the number of huge pages required.
+ */
+ GetHugePageSize(&hp_size, &unused);
+ if (hp_size != 0)
+ {
+ hp_required = (size_b / hp_size) + 1;
+ sprintf(buf, "%zu", hp_required);
+ SetConfigOption("huge_pages_required", buf, PGC_INTERNAL,
PGC_S_OVERRIDE);
+ }
}
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index fd4ca83be1..8edfd07340 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -665,6 +665,7 @@ static int max_identifier_length;
static int block_size;
static int segment_size;
static int shared_memory_size_mb;
+static int huge_pages_required;
static int wal_block_size;
static bool data_checksums;
static bool integer_datetimes;
@@ -2224,6 +2225,17 @@ static struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
+ {
+ {"huge_pages_required", PGC_INTERNAL, PRESET_OPTIONS,
+ gettext_noop("Shows the number of huge pages needed for
the main shared memory area."),
+ gettext_noop("-1 indicates that the value could not be
determined."),
+ GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+ },
+ &huge_pages_required,
+ -1, -1, INT_MAX,
+ NULL, NULL, NULL
+ },
+
{
/* This is PGC_SUSET to prevent hiding from log_lock_waits. */
{"deadlock_timeout", PGC_SUSET, LOCK_MANAGEMENT,
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index ef0e2a7746..b27d8aff15 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10101,6 +10101,27 @@ dynamic_library_path =
'C:\tools\postgresql;H:\my_project\lib;$libdir'
</listitem>
</varlistentry>
+ <varlistentry id="guc-huge-pages-required"
xreflabel="huge_pages_required">
+ <term><varname>huge_pages_required</varname> (<type>integer</type>)
+ <indexterm>
+ <primary><varname>huge_pages_required</varname> configuration
parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ Reports the number of huge pages that are required for the main
+ shared memory area based on the specified
+ <xref linkend="guc-huge-page-size"/>. If huge pages are not supported,
+ this will be <literal>-1</literal>.
+ </para>
+ <para>
+ This setting is supported only on Linux. It is always set to
+ <literal>-1</literal> on other platforms. For more details about using
+ huge pages on Linux, see <xref linkend="linux-huge-pages"/>.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry id="guc-integer-datetimes" xreflabel="integer_datetimes">
<term><varname>integer_datetimes</varname> (<type>boolean</type>)
<indexterm>
--
2.33.0
From f4763273a7f4649d4c50699b590c0b4b8077cb95 Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Thu, 9 Sep 2021 13:10:38 +0900
Subject: [PATCH v9 2/2] Provide useful values for 'postgres -C' with
runtime-computed GUCs.
The -C option is handled before a small subset of GUCs that are
computed at runtime are initialized. Unfortunately, we cannot move
this handling to after they are initialized without disallowing
'postgres -C' on a running server. One notable reason for this is
that loadable libraries' _PG_init() functions are called before all
runtime-computed GUCs are initialized, and this is not guaranteed
to be safe to do on running servers.
In order to provide useful values for 'postgres -C' for runtime-
computed GUCs, this change adds a new section for handling just
these GUCs just before shared memory is initialized. While users
won't be able to use -C for runtime-computed GUCs on running
servers, providing a useful value with this restriction seems
better than not providing a useful value at all.
---
src/include/utils/guc.h | 6 ++++
src/backend/postmaster/postmaster.c | 50 +++++++++++++++++++++++++----
src/backend/utils/misc/guc.c | 10 +++---
doc/src/sgml/ref/postgres-ref.sgml | 12 +++++--
doc/src/sgml/runtime.sgml | 33 +++++++------------
5 files changed, 75 insertions(+), 36 deletions(-)
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index a7c3a4958e..aa18d304ac 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -229,6 +229,12 @@ typedef enum
#define GUC_EXPLAIN 0x100000 /* include in explain */
+/*
+ * GUC_RUNTIME_COMPUTED is intended for runtime-computed GUCs that are only
+ * available via 'postgres -C' if the server is not running.
+ */
+#define GUC_RUNTIME_COMPUTED 0x200000
+
#define GUC_UNIT (GUC_UNIT_MEMORY |
GUC_UNIT_TIME)
diff --git a/src/backend/postmaster/postmaster.c
b/src/backend/postmaster/postmaster.c
index b2fe420c3c..f601b9e5d1 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -896,15 +896,31 @@ PostmasterMain(int argc, char *argv[])
if (output_config_variable != NULL)
{
/*
- * "-C guc" was specified, so print GUC's value and exit. No
extra
- * permission check is needed because the user is reading
inside the
- * data dir.
+ * If this is a runtime-computed GUC, it hasn't yet been
initialized,
+ * and the present value is not useful. However, this is a
convenient
+ * place to print the value for most GUCs because it is safe to
run
+ * postmaster startup to this point even if the server is
already
+ * running. For the handful of runtime-computed GUCs that we
can't
+ * provide meaningful values for yet, we wait until later in
postmaster
+ * startup to print the value. We won't be able to use -C on
running
+ * servers for those GUCs, but otherwise this option is
unusable for
+ * them.
*/
- const char *config_val = GetConfigOption(output_config_variable,
-
false, false);
+ int flags = GetConfigOptionFlags(output_config_variable, true);
- puts(config_val ? config_val : "");
- ExitPostmaster(0);
+ if ((flags & GUC_RUNTIME_COMPUTED) == 0)
+ {
+ /*
+ * "-C guc" was specified, so print GUC's value and
exit. No extra
+ * permission check is needed because the user is
reading inside
+ * the data dir.
+ */
+ const char *config_val =
GetConfigOption(output_config_variable,
+
false, false);
+
+ puts(config_val ? config_val : "");
+ ExitPostmaster(0);
+ }
}
/* Verify that DataDir looks reasonable */
@@ -1033,6 +1049,26 @@ PostmasterMain(int argc, char *argv[])
*/
InitializeShmemGUCs();
+ /*
+ * If -C was specified with a runtime-computed GUC, we held off printing
+ * the value earlier, as the GUC was not yet initialized. We handle -C
for
+ * most GUCs before we lock the data directory so that the option may be
+ * used on a running server. However, a handful of GUCs are runtime-
+ * computed and do not have meaningful values until after locking the
data
+ * directory, and we cannot safely calculate their values earlier on a
+ * running server. At this point, such GUCs should be properly
+ * initialized, and we haven't yet set up shared memory, so this is a
good
+ * time to handle the -C option for these special GUCs.
+ */
+ if (output_config_variable != NULL)
+ {
+ const char *config_val = GetConfigOption(output_config_variable,
+
false, false);
+
+ puts(config_val ? config_val : "");
+ ExitPostmaster(0);
+ }
+
/*
* Set up shared memory and semaphores.
*/
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 8edfd07340..50e60b270b 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1984,7 +1984,7 @@ static struct config_bool ConfigureNamesBool[] =
{"data_checksums", PGC_INTERNAL, PRESET_OPTIONS,
gettext_noop("Shows whether data checksums are turned
on for this cluster."),
NULL,
- GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+ GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE |
GUC_RUNTIME_COMPUTED
},
&data_checksums,
false,
@@ -2229,7 +2229,7 @@ static struct config_int ConfigureNamesInt[] =
{"huge_pages_required", PGC_INTERNAL, PRESET_OPTIONS,
gettext_noop("Shows the number of huge pages needed for
the main shared memory area."),
gettext_noop("-1 indicates that the value could not be
determined."),
- GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+ GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE |
GUC_RUNTIME_COMPUTED
},
&huge_pages_required,
-1, -1, INT_MAX,
@@ -2354,7 +2354,7 @@ static struct config_int ConfigureNamesInt[] =
{"shared_memory_size", PGC_INTERNAL, PRESET_OPTIONS,
gettext_noop("Shows the size of the server's main
shared memory area (rounded up to the nearest MB)."),
NULL,
- GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_UNIT_MB
+ GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_UNIT_MB
| GUC_RUNTIME_COMPUTED
},
&shared_memory_size_mb,
0, 0, INT_MAX,
@@ -2419,7 +2419,7 @@ static struct config_int ConfigureNamesInt[] =
"in the form accepted by the
chmod and umask system "
"calls. (To use the customary
octal format the number "
"must start with a 0
(zero).)"),
- GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+ GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE |
GUC_RUNTIME_COMPUTED
},
&data_directory_mode,
0700, 0000, 0777,
@@ -3243,7 +3243,7 @@ static struct config_int ConfigureNamesInt[] =
{"wal_segment_size", PGC_INTERNAL, PRESET_OPTIONS,
gettext_noop("Shows the size of write ahead log
segments."),
NULL,
- GUC_UNIT_BYTE | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+ GUC_UNIT_BYTE | GUC_NOT_IN_SAMPLE |
GUC_DISALLOW_IN_FILE | GUC_RUNTIME_COMPUTED
},
&wal_segment_size,
DEFAULT_XLOG_SEG_SIZE,
diff --git a/doc/src/sgml/ref/postgres-ref.sgml
b/doc/src/sgml/ref/postgres-ref.sgml
index 4aaa7abe1a..89cc3cdb4e 100644
--- a/doc/src/sgml/ref/postgres-ref.sgml
+++ b/doc/src/sgml/ref/postgres-ref.sgml
@@ -133,13 +133,21 @@ PostgreSQL documentation
<listitem>
<para>
Prints the value of the named run-time parameter, and exits.
- (See the <option>-c</option> option above for details.) This can
- be used on a running server, and returns values from
+ (See the <option>-c</option> option above for details.) This
+ returns values from
<filename>postgresql.conf</filename>, modified by any parameters
supplied in this invocation. It does not reflect parameters
supplied when the cluster was started.
</para>
+ <para>
+ This can be used on a running server for most parameters. However,
+ the server must be shut down for some runtime-computed parameters
+ (e.g., <xref linkend="guc-huge-pages-required"/>,
+ <xref linkend="guc-shared-memory-size"/>, and
+ <xref linkend="guc-wal-segment-size"/>).
+ </para>
+
<para>
This option is meant for other programs that interact with a server
instance, such as <xref linkend="app-pg-ctl"/>, to query configuration
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index f1cbc1d9e9..d955639900 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1442,32 +1442,21 @@ export PG_OOM_ADJUST_VALUE=0
with <varname>CONFIG_HUGETLBFS=y</varname> and
<varname>CONFIG_HUGETLB_PAGE=y</varname>. You will also have to configure
the operating system to provide enough huge pages of the desired size.
- To estimate the number of huge pages needed, start
- <productname>PostgreSQL</productname> without huge pages enabled and check
- the postmaster's anonymous shared memory segment size, as well as the
- system's default and supported huge page sizes, using the
- <filename>/proc</filename> and <filename>/sys</filename> file systems.
- This might look like:
+ To estimate the number of huge pages needed, use the
+ <command>postgres</command> command to see the value of
+ <xref linkend="guc-huge-pages-required"/>. This might look like:
<programlisting>
-$ <userinput>head -1 $PGDATA/postmaster.pid</userinput>
-4170
-$ <userinput>pmap 4170 | awk '/rw-s/ && /zero/ {print $2}'</userinput>
-6490428K
-$ <userinput>grep ^Hugepagesize /proc/meminfo</userinput>
-Hugepagesize: 2048 kB
-$ <userinput>ls /sys/kernel/mm/hugepages</userinput>
-hugepages-1048576kB hugepages-2048kB
+$ <userinput>postgres -D $PGDATA -C huge_pages_required</userinput>
+3170
</programlisting>
- In this example the default is 2MB, but you can also explicitly request
- either 2MB or 1GB with <xref linkend="guc-huge-page-size"/>.
+ Note that you can explicitly request either 2MB or 1GB huge pages with
+ <xref linkend="guc-huge-page-size"/>.
- Assuming <literal>2MB</literal> huge pages,
- <literal>6490428</literal> / <literal>2048</literal> gives approximately
- <literal>3169.154</literal>, so in this example we need at
- least <literal>3170</literal> huge pages. A larger setting would be
- appropriate if other programs on the machine also need huge pages.
- We can set this with:
+ While we need at least <literal>3170</literal> huge pages in this
+ example, a larger setting would be appropriate if other programs on
+ the machine also need huge pages. We can allocate the huge pages
+ with:
<programlisting>
# <userinput>sysctl -w vm.nr_hugepages=3170</userinput>
</programlisting>
--
2.33.0
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