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Commit8722017

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committed
Allow dynamic shared memory segments to be kept until shutdown.
Amit Kapila, reviewed by Kyotaro Horiguchi, with some furtherchanges by me.
1 parent5a991ef commit8722017

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4 files changed

+75
-1
lines changed

4 files changed

+75
-1
lines changed

‎src/backend/storage/ipc/dsm.c‎

Lines changed: 27 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -885,6 +885,33 @@ dsm_keep_mapping(dsm_segment *seg)
885885
}
886886
}
887887

888+
/*
889+
* Keep a dynamic shared memory segment until postmaster shutdown.
890+
*
891+
* This function should not be called more than once per segment;
892+
* on Windows, doing so will create unnecessary handles which will
893+
* consume system resources to no benefit.
894+
*
895+
* Note that this function does not arrange for the current process to
896+
* keep the segment mapped indefinitely; if that behavior is desired,
897+
* dsm_keep_mapping() should be used from each process that needs to
898+
* retain the mapping.
899+
*/
900+
void
901+
dsm_keep_segment(dsm_segment*seg)
902+
{
903+
/*
904+
* Bump reference count for this segment in shared memory. This will
905+
* ensure that even if there is no session which is attached to this
906+
* segment, it will remain until postmaster shutdown.
907+
*/
908+
LWLockAcquire(DynamicSharedMemoryControlLock,LW_EXCLUSIVE);
909+
dsm_control->item[seg->control_slot].refcnt++;
910+
LWLockRelease(DynamicSharedMemoryControlLock);
911+
912+
dsm_impl_keep_segment(seg->handle,seg->impl_private);
913+
}
914+
888915
/*
889916
* Find an existing mapping for a shared memory segment, if there is one.
890917
*/

‎src/backend/storage/ipc/dsm_impl.c‎

Lines changed: 44 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -67,6 +67,7 @@
6767
#include"storage/fd.h"
6868
#include"utils/guc.h"
6969
#include"utils/memutils.h"
70+
#include"postmaster/postmaster.h"
7071

7172
#ifdefUSE_DSM_POSIX
7273
staticbooldsm_impl_posix(dsm_opop,dsm_handlehandle,Sizerequest_size,
@@ -113,6 +114,8 @@ int dynamic_shared_memory_type;
113114
/* Size of buffer to be used for zero-filling. */
114115
#defineZBUFFER_SIZE8192
115116

117+
#defineSEGMENT_NAME_PREFIX"Global/PostgreSQL"
118+
116119
/*------
117120
* Perform a low-level shared memory operation in a platform-specific way,
118121
* as dictated by the selected implementation. Each implementation is
@@ -635,7 +638,7 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
635638
* convention similar to main shared memory. We can change here once
636639
* issue mentioned in GetSharedMemName is resolved.
637640
*/
638-
snprintf(name,64,"Global/PostgreSQL.%u",handle);
641+
snprintf(name,64,"%s.%u",SEGMENT_NAME_PREFIX,handle);
639642

640643
/*
641644
* Handle teardown cases. Since Windows automatically destroys the object
@@ -982,6 +985,46 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
982985
}
983986
#endif
984987

988+
/*
989+
* Implementation-specific actions that must be performed when a segment
990+
* is to be preserved until postmaster shutdown.
991+
*
992+
* Except on Windows, we don't need to do anything at all. But since Windows
993+
* cleans up segments automatically when no references remain, we duplicate
994+
* the segment handle into the postmaster process. The postmaster needn't
995+
* do anything to receive the handle; Windows transfers it automatically.
996+
*/
997+
void
998+
dsm_impl_keep_segment(dsm_handlehandle,void*impl_private)
999+
{
1000+
switch (dynamic_shared_memory_type)
1001+
{
1002+
#ifdefUSE_DSM_WINDOWS
1003+
caseDSM_IMPL_WINDOWS:
1004+
{
1005+
HANDLEhmap;
1006+
1007+
if (!DuplicateHandle(GetCurrentProcess(),impl_private,
1008+
PostmasterHandle,&hmap,0, FALSE,
1009+
DUPLICATE_SAME_ACCESS))
1010+
{
1011+
charname[64];
1012+
1013+
snprintf(name,64,"%s.%u",SEGMENT_NAME_PREFIX,handle);
1014+
_dosmaperr(GetLastError());
1015+
ereport(ERROR,
1016+
(errcode_for_dynamic_shared_memory(),
1017+
errmsg("could not duplicate handle for \"%s\": %m",
1018+
name)));
1019+
}
1020+
break;
1021+
}
1022+
#endif
1023+
default:
1024+
break;
1025+
}
1026+
}
1027+
9851028
staticint
9861029
errcode_for_dynamic_shared_memory()
9871030
{

‎src/include/storage/dsm.h‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -30,6 +30,7 @@ extern void dsm_detach(dsm_segment *seg);
3030

3131
/* Resource management functions. */
3232
externvoiddsm_keep_mapping(dsm_segment*seg);
33+
externvoiddsm_keep_segment(dsm_segment*seg);
3334
externdsm_segment*dsm_find_mapping(dsm_handleh);
3435

3536
/* Informational functions. */

‎src/include/storage/dsm_impl.h‎

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -72,4 +72,7 @@ extern bool dsm_impl_op(dsm_op op, dsm_handle handle, Size request_size,
7272
/* Some implementations cannot resize segments. Can this one? */
7373
externbooldsm_impl_can_resize(void);
7474

75+
/* Implementation-dependent actions required to keep segment until shudown. */
76+
externvoiddsm_impl_keep_segment(dsm_handlehandle,void*impl_private);
77+
7578
#endif/* DSM_IMPL_H */

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