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Commitf1bebef

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Add shared_memory_type GUC.
Since 9.3 we have used anonymous shared mmap for our main shared memoryregion, except in EXEC_BACKEND builds. Provide a GUC so that userscan opt for System V shared memory once again, like in 9.2 and earlier.A later patch proposes to add huge/large page support for AIX, whichrequires System V shared memory and provided the motivation to revivethis possibility. It may also be useful on some BSDs.Author: Andres Freund (revived and documented by Thomas Munro)Discussion:https://postgr.es/m/HE1PR0202MB28126DB4E0B6621CC6A1A91286D90%40HE1PR0202MB2812.eurprd02.prod.outlook.comDiscussion:https://postgr.es/m/2AE143D2-87D3-4AD1-AC78-CE2258230C05%40FreeBSD.org
1 parent0d1fe9f commitf1bebef

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7 files changed

+101
-33
lines changed

7 files changed

+101
-33
lines changed

‎doc/src/sgml/config.sgml

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Original file line numberDiff line numberDiff line change
@@ -1694,6 +1694,31 @@ include_dir 'conf.d'
16941694
</listitem>
16951695
</varlistentry>
16961696

1697+
<varlistentry id="guc-shared-memory-type" xreflabel="shared_memory_type">
1698+
<term><varname>shared_memory_type</varname> (<type>enum</type>)
1699+
<indexterm>
1700+
<primary><varname>shared_memory_type</varname> configuration parameter</primary>
1701+
</indexterm>
1702+
</term>
1703+
<listitem>
1704+
<para>
1705+
Specifies the shared memory implementation that the server
1706+
should use for the main shared memory region that holds
1707+
<productname>PostgreSQL</productname>'s shared buffers and other
1708+
shared data. Possible values are <literal>mmap</literal> (for
1709+
anonymous shared memory allocated using <function>mmap</function>),
1710+
<literal>sysv</literal> (for System V shared memory allocated via
1711+
<function>shmget</function>) and <literal>windows</literal> (for Windows
1712+
shared memory). Not all values are supported on all platforms; the
1713+
first supported option is the default for that platform. The use of
1714+
the <literal>sysv</literal> option, which is not the default on any
1715+
platform, is generally discouraged because it typically requires
1716+
non-default kernel settings to allow for large allocations (see <xref
1717+
linkend="sysvipc"/>).
1718+
</para>
1719+
</listitem>
1720+
</varlistentry>
1721+
16971722
<varlistentry id="guc-dynamic-shared-memory-type" xreflabel="dynamic_shared_memory_type">
16981723
<term><varname>dynamic_shared_memory_type</varname> (<type>enum</type>)
16991724
<indexterm>

‎doc/src/sgml/runtime.sgml

Lines changed: 11 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -638,9 +638,12 @@ psql: could not connect to server: No such file or directory
638638
</para>
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640640
<para>
641-
Upon starting the server, <productname>PostgreSQL</productname> normally allocates
641+
By default, <productname>PostgreSQL</productname> allocates
642642
a very small amount of System V shared memory, as well as a much larger
643-
amount of POSIX (<function>mmap</function>) shared memory.
643+
amount of anonymous <function>mmap</function> shared memory.
644+
Alternatively, a single large System V shared memory region can be used
645+
(see <xref linkend="guc-shared-memory-type"/>).
646+
644647
In addition a significant number of semaphores, which can be either
645648
System V or POSIX style, are created at server startup. Currently,
646649
POSIX semaphores are used on Linux and FreeBSD systems while other
@@ -752,8 +755,10 @@ psql: could not connect to server: No such file or directory
752755
<productname>PostgreSQL</productname> requires a few bytes of System V shared memory
753756
(typically 48 bytes, on 64-bit platforms) for each copy of the server.
754757
On most modern operating systems, this amount can easily be allocated.
755-
However, if you are running many copies of the server, or if other
756-
applications are also using System V shared memory, it may be necessary to
758+
However, if you are running many copies of the server or you explicitly
759+
configure the server to use large amounts of System V shared memory (see
760+
<xref linkend="guc-shared-memory-type"/> and <xref
761+
linkend="guc-dynamic-shared-memory-type"/>), it may be necessary to
757762
increase <varname>SHMALL</varname>, which is the total amount of System V shared
758763
memory system-wide. Note that <varname>SHMALL</varname> is measured in pages
759764
rather than bytes on many systems.
@@ -879,7 +884,7 @@ kern.ipc.semmns=512
879884
</para>
880885

881886
<para>
882-
You might also want to configure your kernel to lock shared
887+
You might also want to configure your kernel to lockSystem Vshared
883888
memory into RAM and prevent it from being paged out to swap.
884889
This can be accomplished using the <command>sysctl</command>
885890
setting <literal>kern.ipc.shm_use_phys</literal>.
@@ -928,7 +933,7 @@ kern.ipc.semmns=512
928933
</para>
929934

930935
<para>
931-
You might also want to configure your kernel to lock shared
936+
You might also want to configure your kernel to lockSystem Vshared
932937
memory into RAM and prevent it from being paged out to swap.
933938
This can be accomplished using the <command>sysctl</command>
934939
setting <literal>kern.ipc.shm_use_phys</literal>.

‎src/backend/port/sysv_shmem.c

Lines changed: 16 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -62,10 +62,11 @@
6262
* to a process after exec(). Since EXEC_BACKEND is intended only for
6363
* developer use, this shouldn't be a big problem. Because of this, we do
6464
* not worry about supporting anonymous shmem in the EXEC_BACKEND cases below.
65+
*
66+
* As of PostgreSQL 12, we regained the ability to use a large System V shared
67+
* memory region even in non-EXEC_BACKEND builds, if shared_memory_type is set
68+
* to sysv (though this is not the default).
6569
*/
66-
#ifndefEXEC_BACKEND
67-
#defineUSE_ANONYMOUS_SHMEM
68-
#endif
6970

7071

7172
typedefkey_tIpcMemoryKey;/* shared memory key passed to shmget(2) */
@@ -75,10 +76,8 @@ typedef int IpcMemoryId;/* shared memory ID returned by shmget(2) */
7576
unsigned longUsedShmemSegID=0;
7677
void*UsedShmemSegAddr=NULL;
7778

78-
#ifdefUSE_ANONYMOUS_SHMEM
7979
staticSizeAnonymousShmemSize;
8080
staticvoid*AnonymousShmem=NULL;
81-
#endif
8281

8382
staticvoid*InternalIpcMemoryCreate(IpcMemoryKeymemKey,Sizesize);
8483
staticvoidIpcMemoryDetach(intstatus,Datumshmaddr);
@@ -370,8 +369,6 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
370369
return true;
371370
}
372371

373-
#ifdefUSE_ANONYMOUS_SHMEM
374-
375372
#ifdefMAP_HUGETLB
376373

377374
/*
@@ -534,8 +531,6 @@ AnonymousShmemDetach(int status, Datum arg)
534531
}
535532
}
536533

537-
#endif/* USE_ANONYMOUS_SHMEM */
538-
539534
/*
540535
* PGSharedMemoryCreate
541536
*
@@ -566,7 +561,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
566561
Sizesysvsize;
567562

568563
/* Complain if hugepages demanded but we can't possibly support them */
569-
#if !defined(USE_ANONYMOUS_SHMEM)|| !defined(MAP_HUGETLB)
564+
#if !defined(MAP_HUGETLB)
570565
if (huge_pages==HUGE_PAGES_ON)
571566
ereport(ERROR,
572567
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -576,18 +571,19 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
576571
/* Room for a header? */
577572
Assert(size>MAXALIGN(sizeof(PGShmemHeader)));
578573

579-
#ifdefUSE_ANONYMOUS_SHMEM
580-
AnonymousShmem=CreateAnonymousSegment(&size);
581-
AnonymousShmemSize=size;
574+
if (shared_memory_type==SHMEM_TYPE_MMAP)
575+
{
576+
AnonymousShmem=CreateAnonymousSegment(&size);
577+
AnonymousShmemSize=size;
582578

583-
/* Register on-exit routine to unmap the anonymous segment */
584-
on_shmem_exit(AnonymousShmemDetach, (Datum)0);
579+
/* Register on-exit routine to unmap the anonymous segment */
580+
on_shmem_exit(AnonymousShmemDetach, (Datum)0);
585581

586-
/* Now we need only allocate a minimal-sized SysV shmem block. */
587-
sysvsize=sizeof(PGShmemHeader);
588-
#else
589-
sysvsize=size;
590-
#endif
582+
/* Now we need only allocate a minimal-sized SysV shmem block. */
583+
sysvsize=sizeof(PGShmemHeader);
584+
}
585+
else
586+
sysvsize=size;
591587

592588
/* Make sure PGSharedMemoryAttach doesn't fail without need */
593589
UsedShmemSegAddr=NULL;
@@ -687,14 +683,10 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
687683
* block. Otherwise, the System V shared memory block is only a shim, and
688684
* we must return a pointer to the real block.
689685
*/
690-
#ifdefUSE_ANONYMOUS_SHMEM
691686
if (AnonymousShmem==NULL)
692687
returnhdr;
693688
memcpy(AnonymousShmem,hdr,sizeof(PGShmemHeader));
694689
return (PGShmemHeader*)AnonymousShmem;
695-
#else
696-
returnhdr;
697-
#endif
698690
}
699691

700692
#ifdefEXEC_BACKEND
@@ -801,15 +793,13 @@ PGSharedMemoryDetach(void)
801793
UsedShmemSegAddr=NULL;
802794
}
803795

804-
#ifdefUSE_ANONYMOUS_SHMEM
805796
if (AnonymousShmem!=NULL)
806797
{
807798
if (munmap(AnonymousShmem,AnonymousShmemSize)<0)
808799
elog(LOG,"munmap(%p, %zu) failed: %m",
809800
AnonymousShmem,AnonymousShmemSize);
810801
AnonymousShmem=NULL;
811802
}
812-
#endif
813803
}
814804

815805

‎src/backend/storage/ipc/ipci.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -46,6 +46,8 @@
4646
#include"storage/spin.h"
4747
#include"utils/snapmgr.h"
4848

49+
/* GUCs */
50+
intshared_memory_type=DEFAULT_SHARED_MEMORY_TYPE;
4951

5052
shmem_startup_hook_typeshmem_startup_hook=NULL;
5153

‎src/backend/utils/misc/guc.c

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -453,6 +453,19 @@ const struct config_enum_entry ssl_protocol_versions_info[] = {
453453
{NULL,0, false}
454454
};
455455

456+
staticstructconfig_enum_entryshared_memory_options[]= {
457+
#ifndefWIN32
458+
{"sysv",SHMEM_TYPE_SYSV, false},
459+
#endif
460+
#ifndefEXEC_BACKEND
461+
{"mmap",SHMEM_TYPE_MMAP, false},
462+
#endif
463+
#ifdefWIN32
464+
{"windows",SHMEM_TYPE_WINDOWS, false},
465+
#endif
466+
{NULL,0, false}
467+
};
468+
456469
/*
457470
* Options for enum values stored in other modules
458471
*/
@@ -4327,6 +4340,16 @@ static struct config_enum ConfigureNamesEnum[] =
43274340
NULL,NULL,NULL
43284341
},
43294342

4343+
{
4344+
{"shared_memory_type",PGC_POSTMASTER,RESOURCES_MEM,
4345+
gettext_noop("Selects the shared memory implementation used for the main shared memory region."),
4346+
NULL
4347+
},
4348+
&shared_memory_type,
4349+
DEFAULT_SHARED_MEMORY_TYPE,shared_memory_options,
4350+
NULL,NULL,NULL
4351+
},
4352+
43304353
{
43314354
{"wal_sync_method",PGC_SIGHUP,WAL_SETTINGS,
43324355
gettext_noop("Selects the method used for forcing WAL updates to disk."),

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

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -129,6 +129,12 @@
129129
#maintenance_work_mem = 64MB# min 1MB
130130
#autovacuum_work_mem = -1# min 1MB, or -1 to use maintenance_work_mem
131131
#max_stack_depth = 2MB# min 100kB
132+
#shared_memory_type = mmap# the default is the first option
133+
# supported by the operating system:
134+
# mmap
135+
# sysv
136+
# windows
137+
# (change requires restart)
132138
#dynamic_shared_memory_type = posix# the default is the first option
133139
# supported by the operating system:
134140
# posix

‎src/include/storage/pg_shmem.h

Lines changed: 18 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -41,7 +41,8 @@ typedef struct PGShmemHeader/* standard header for all Postgres shmem */
4141
#endif
4242
}PGShmemHeader;
4343

44-
/* GUC variable */
44+
/* GUC variables */
45+
externintshared_memory_type;
4546
externinthuge_pages;
4647

4748
/* Possible values for huge_pages */
@@ -52,13 +53,29 @@ typedef enum
5253
HUGE_PAGES_TRY
5354
}HugePagesType;
5455

56+
/* Possible values for shared_memory_type */
57+
typedefenum
58+
{
59+
SHMEM_TYPE_WINDOWS,
60+
SHMEM_TYPE_SYSV,
61+
SHMEM_TYPE_MMAP
62+
}PGShmemType;
63+
5564
#ifndefWIN32
5665
externunsigned longUsedShmemSegID;
5766
#else
5867
externHANDLEUsedShmemSegID;
5968
#endif
6069
externvoid*UsedShmemSegAddr;
6170

71+
#if !defined(WIN32)&& !defined(EXEC_BACKEND)
72+
#defineDEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_MMAP
73+
#elif !defined(WIN32)
74+
#defineDEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_SYSV
75+
#else
76+
#defineDEFAULT_SHARED_MEMORY_TYPE SHMEM_TYPE_WINDOWS
77+
#endif
78+
6279
#ifdefEXEC_BACKEND
6380
externvoidPGSharedMemoryReAttach(void);
6481
externvoidPGSharedMemoryNoReAttach(void);

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