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Get rid of the dynamic shared memory state file.

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Instead of storing the ID of the dynamic shared memory control
segment in a file within the data directory, store it in the main
control segment.  This avoids a number of nasty corner cases,
most seriously that doing an online backup and then using it on
the same machine (e.g. to fire up a standby) would result in the
standby clobbering all of the master's dynamic shared memory
segments.

Per complaints from Heikki Linnakangas, Fujii Masao, and Tom
Lane.
This commit is contained in:
Robert Haas
2014-04-08 11:39:55 -04:00
parent 0886fc6a5c
commit 11a65eed16
6 changed files with 71 additions and 166 deletions
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12
src/backend/port/sysv_shmem.c
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@ -30,6 +30,7 @@
#include "miscadmin.h"
#include "portability/mem.h"
#include "storage/dsm.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "utils/guc.h"
@ -421,7 +422,8 @@ CreateAnonymousSegment(Size *size)
* zero will be passed.
*/
PGShmemHeader *
PGSharedMemoryCreate(Size size, bool makePrivate, int port)
PGSharedMemoryCreate(Size size, bool makePrivate, int port,
PGShmemHeader **shim)
{
IpcMemoryKey NextShmemSegID;
void *memAddress;
@ -509,10 +511,13 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
/*
* The segment appears to be from a dead Postgres process, or from a
* previous cycle of life in this same process. Zap it, if possible.
* previous cycle of life in this same process. Zap it, if possible,
* and any associated dynamic shared memory segments, as well.
* This probably shouldn't fail, but if it does, assume the segment
* belongs to someone else after all, and continue quietly.
*/
if (hdr->dsm_control != 0)
dsm_cleanup_using_control_segment(hdr->dsm_control);
shmdt(memAddress);
if (shmctl(shmid, IPC_RMID, NULL) < 0)
continue;
@ -539,6 +544,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
hdr = (PGShmemHeader *) memAddress;
hdr->creatorPID = getpid();
hdr->magic = PGShmemMagic;
hdr->dsm_control = 0;
/* Fill in the data directory ID info, too */
if (stat(DataDir, &statbuf) < 0)
@ -554,6 +560,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
*/
hdr->totalsize = size;
hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
*shim = hdr;
/* Save info for possible future use */
UsedShmemSegAddr = memAddress;
@ -608,6 +615,7 @@ PGSharedMemoryReAttach(void)
if (hdr != origUsedShmemSegAddr)
elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
hdr, origUsedShmemSegAddr);
dsm_set_control_handle(((PGShmemHeader *) hdr)->dsm_control);
UsedShmemSegAddr = hdr; /* probably redundant */
}