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);
        }