Cause stats processes to detach from shared memory when started, so that

they do not prevent the postmaster from deleting the shmem segment during
a post-backend-crash restart cycle.  Per recent discussion.

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 243eb29082a7512f5fb94b299a25b18381d09307..0a5f19a5ef4095dbec1a0f9d1ea754010c5610ce 100644 (file)
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -134,7 +134,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size)
 
        /* OK, should be able to attach to the segment */
 #ifdef SHM_SHARE_MMU
-       /* use intimate shared memory on SPARC Solaris */
+       /* use intimate shared memory on Solaris */
        memAddress = shmat(shmid, 0, SHM_SHARE_MMU);
 #else
        memAddress = shmat(shmid, 0, 0);
@@ -244,7 +244,7 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
        /* Room for a header? */
        Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
 
-       /* Just attach and return the pointer */
+       /* If Exec case, just attach and return the pointer */
        if (ExecBackend && UsedShmemSegAddr != NULL && !makePrivate)
        {
                if ((hdr = PGSharedMemoryAttach(UsedShmemSegID, &shmid)) == NULL)
@@ -253,6 +253,9 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
                return hdr;
        }
 
+       /* Make sure PGSharedMemoryAttach doesn't fail without need */
+       UsedShmemSegAddr = NULL;
+
        /* Loop till we find a free IPC key */
        NextShmemSegID = port * 1000;
 
@@ -326,16 +329,32 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
        hdr->totalsize = size;
        hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
 
-
-       if (ExecBackend && UsedShmemSegAddr == NULL && !makePrivate)
-       {
-               UsedShmemSegAddr = memAddress;
-               UsedShmemSegID = NextShmemSegID;
-       }
+       /* Save info for possible future use */
+       UsedShmemSegAddr = memAddress;
+       UsedShmemSegID = NextShmemSegID;
 
        return hdr;
 }
 
+/*
+ * PGSharedMemoryDetach
+ *
+ * Detach from the shared memory segment, if still attached.  This is not
+ * intended for use by the process that originally created the segment
+ * (it will have an on_shmem_exit callback registered to do that).  Rather,
+ * this is for subprocesses that have inherited an attachment and want to
+ * get rid of it.
+ */
+void
+PGSharedMemoryDetach(void)
+{
+       if (UsedShmemSegAddr != NULL)
+       {
+               if (shmdt(UsedShmemSegAddr) < 0)
+                       elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
+               UsedShmemSegAddr = NULL;
+       }
+}
 
 /*
  * Attach to shared memory and make sure it has a Postgres header

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 660dedfd8064ca2700156a4ec13f427c14b99f53..3edc28b8a10067713aa8bbff38908f9a9932b416 100644 (file)
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -44,6 +44,7 @@
 #include "utils/memutils.h"
 #include "storage/backendid.h"
 #include "storage/ipc.h"
+#include "storage/pg_shmem.h"
 #include "utils/rel.h"
 #include "utils/hsearch.h"
 #include "utils/ps_status.h"
@@ -400,6 +401,9 @@ pgstat_start(void)
        /* Close the postmaster's sockets, except for pgstat link */
        ClosePostmasterPorts(false);
 
+       /* Drop our connection to postmaster's shared memory, as well */
+       PGSharedMemoryDetach();
+
        pgstat_main();
 
        exit(0);

diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 2c3d72d771c936b8146a6c0775c2e593567d1a51..4b9f3ca63a0d9c1a407889cae8389ffd1489ff3e 100644 (file)
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -44,5 +44,6 @@ extern void *UsedShmemSegAddr;
 extern PGShmemHeader *PGSharedMemoryCreate(uint32 size, bool makePrivate,
                                         int port);
 extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
+extern void PGSharedMemoryDetach(void);
 
 #endif   /* PG_SHMEM_H */