Make backends that are reading the pgstats file verify each backend PID

against the PGPROC array.  Anything in the file that isn't in PGPROC
gets rejected as being a stale entry.  This should solve complaints about
stale entries in pg_stat_activity after a BETERM message has been dropped
due to overload.

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 9a07915f79b2ea51a1bfa7b076dad11f2cfa5b3a..00ed7b837da71ccbb1c7a1aa848efef92ab8248b 100644 (file)
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -13,7 +13,7 @@
  *
  * Copyright (c) 2001-2005, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.103 2005/08/08 03:11:40 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.104 2005/08/09 21:14:55 tgl Exp $
  * ----------
  */
 #include "postgres.h"
@@ -46,6 +46,7 @@
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"
 #include "storage/pmsignal.h"
+#include "storage/procarray.h"
 #include "tcop/tcopprot.h"
 #include "utils/hsearch.h"
 #include "utils/memutils.h"
@@ -1605,8 +1606,8 @@ PgstatCollectorMain(int argc, char *argv[])
    /*
     * Create the known backends table
     */
-   pgStatBeTable = (PgStat_StatBeEntry *) palloc0(
-                              sizeof(PgStat_StatBeEntry) * MaxBackends);
+   pgStatBeTable = (PgStat_StatBeEntry *)
+       palloc0(sizeof(PgStat_StatBeEntry) * MaxBackends);
 
    readPipe = pgStatPipe[0];
 
@@ -2456,6 +2457,7 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
    PgStat_StatDBEntry dbbuf;
    PgStat_StatTabEntry *tabentry;
    PgStat_StatTabEntry tabbuf;
+   PgStat_StatBeEntry *beentry;
    HASHCTL     hash_ctl;
    HTAB       *tabhash = NULL;
    FILE       *fpin;
@@ -2463,6 +2465,7 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
    int         maxbackends = 0;
    int         havebackends = 0;
    bool        found;
+   bool        check_pids;
    MemoryContext use_mcxt;
    int         mcxt_flags;
 
@@ -2472,16 +2475,22 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
     * TopTransactionContext instead, so the caller must only know the last
     * XactId when this call happened to know if his tables are still valid or
     * already gone!
+    *
+    * Also, if running in a regular backend, we check backend entries against
+    * the PGPROC array so that we can detect stale entries.  This lets us
+    * discard entries whose BETERM message got lost for some reason.
     */
    if (pgStatRunningInCollector || IsAutoVacuumProcess())
    {
        use_mcxt = NULL;
        mcxt_flags = 0;
+       check_pids = false;
    }
    else
    {
        use_mcxt = TopTransactionContext;
        mcxt_flags = HASH_CONTEXT;
+       check_pids = true;
    }
 
    /*
@@ -2665,11 +2674,15 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
                if (betab == NULL || numbackends == NULL || *betab == NULL)
                    goto done;
 
+               if (havebackends >= maxbackends)
+                   goto done;
+
                /*
                 * Read it directly into the table.
                 */
-               if (fread(&(*betab)[havebackends], 1,
-                         sizeof(PgStat_StatBeEntry), fpin) !=
+               beentry = &(*betab)[havebackends];
+
+               if (fread(beentry, 1, sizeof(PgStat_StatBeEntry), fpin) !=
                    sizeof(PgStat_StatBeEntry))
                {
                    ereport(pgStatRunningInCollector ? LOG : WARNING,
@@ -2677,20 +2690,36 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
                    goto done;
                }
 
+               /*
+                * If possible, check PID to verify still running
+                */
+               if (check_pids && !IsBackendPid(beentry->procpid))
+               {
+                   /*
+                    * Note: we could send a BETERM message to tell the
+                    * collector to drop the entry, but I'm a bit worried
+                    * about race conditions.  For now, just silently ignore
+                    * dead entries; they'll get recycled eventually anyway.
+                    */
+
+                   /* Don't accept the entry */
+                   memset(beentry, 0, sizeof(PgStat_StatBeEntry));
+                   break;
+               }
+
                /*
                 * Count backends per database here.
                 */
-               dbentry = (PgStat_StatDBEntry *) hash_search(*dbhash,
-                          (void *) &((*betab)[havebackends].databaseid),
-                                                       HASH_FIND, NULL);
+               dbentry = (PgStat_StatDBEntry *)
+                   hash_search(*dbhash,
+                               &(beentry->databaseid),
+                               HASH_FIND,
+                               NULL);
                if (dbentry)
                    dbentry->n_backends++;
 
                havebackends++;
-               if (numbackends != 0)
-                   *numbackends = havebackends;
-               if (havebackends >= maxbackends)
-                   goto done;
+               *numbackends = havebackends;
 
                break;
 
@@ -2728,10 +2757,10 @@ backend_read_statsfile(void)
 {
    if (IsAutoVacuumProcess())
    {
-       Assert(!pgStatRunningInCollector);
        /* already read it? */
        if (pgStatDBHash)
            return;
+       Assert(!pgStatRunningInCollector);
        pgstat_read_statsfile(&pgStatDBHash, InvalidOid,
                              &pgStatBeTable, &pgStatNumBackends);
    }