Avoid crashing when a table is deleted while we're on the process of checking

it.

Per report from Tom Lane based on buildfarm evidence.

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 9ed34eed6f824e6012b3f77be9c7f0ae0cffe4cd..f3405f4352e921311805e9464f70cfa84daaf594 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -55,7 +55,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.80 2008/07/01 02:09:34 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.81 2008/07/17 21:02:31 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -176,6 +176,9 @@ typedef struct autovac_table
    int         at_vacuum_cost_delay;
    int         at_vacuum_cost_limit;
    bool        at_wraparound;
+   char       *at_relname;
+   char       *at_nspname;
+   char       *at_datname;
 } autovac_table;
 
 /*-------------
@@ -282,15 +285,13 @@ static void relation_needs_vacanalyze(Oid relid, Form_pg_autovacuum avForm,
                          PgStat_StatTabEntry *tabentry, bool *dovacuum,
                          bool *doanalyze, bool *wraparound);
 
-static void autovacuum_do_vac_analyze(Oid relid, bool dovacuum,
-                         bool doanalyze, int freeze_min_age,
-                         bool for_wraparound,
+static void autovacuum_do_vac_analyze(autovac_table *tab,
                          BufferAccessStrategy bstrategy);
 static HeapTuple get_pg_autovacuum_tuple_relid(Relation avRel, Oid relid);
 static PgStat_StatTabEntry *get_pgstat_tabentry_relid(Oid relid, bool isshared,
                          PgStat_StatDBEntry *shared,
                          PgStat_StatDBEntry *dbentry);
-static void autovac_report_activity(VacuumStmt *vacstmt, Oid relid);
+static void autovac_report_activity(autovac_table *tab);
 static void avl_sighup_handler(SIGNAL_ARGS);
 static void avl_sigusr1_handler(SIGNAL_ARGS);
 static void avl_sigterm_handler(SIGNAL_ARGS);
@@ -2061,9 +2062,6 @@ do_autovacuum(void)
        autovac_table *tab;
        WorkerInfo  worker;
        bool        skipit;
-       char       *datname,
-                  *nspname,
-                  *relname;
 
        CHECK_FOR_INTERRUPTS();
 
@@ -2158,13 +2156,17 @@ do_autovacuum(void)
 
        /*
         * Save the relation name for a possible error message, to avoid a
-        * catalog lookup in case of an error.  Note: they must live in a
-        * long-lived memory context because we call vacuum and analyze in
-        * different transactions.
+        * catalog lookup in case of an error.  If any of these return NULL,
+        * then the relation has been dropped since last we checked; skip it.
+        * Note: they must live in a long-lived memory context because we call
+        * vacuum and analyze in different transactions.
         */
-       datname = get_database_name(MyDatabaseId);
-       nspname = get_namespace_name(get_rel_namespace(tab->at_relid));
-       relname = get_rel_name(tab->at_relid);
+
+       tab->at_relname = get_rel_name(tab->at_relid);
+       tab->at_nspname = get_namespace_name(get_rel_namespace(tab->at_relid));
+       tab->at_datname = get_database_name(MyDatabaseId);
+       if (!tab->at_relname || !tab->at_nspname || !tab->at_datname)
+           goto deleted;
 
        /*
         * We will abort vacuuming the current table if something errors out,
@@ -2175,12 +2177,7 @@ do_autovacuum(void)
        {
            /* have at it */
            MemoryContextSwitchTo(TopTransactionContext);
-           autovacuum_do_vac_analyze(tab->at_relid,
-                                     tab->at_dovacuum,
-                                     tab->at_doanalyze,
-                                     tab->at_freeze_min_age,
-                                     tab->at_wraparound,
-                                     bstrategy);
+           autovacuum_do_vac_analyze(tab, bstrategy);
 
            /*
             * Clear a possible query-cancel signal, to avoid a late reaction
@@ -2199,10 +2196,10 @@ do_autovacuum(void)
            HOLD_INTERRUPTS();
            if (tab->at_dovacuum)
                errcontext("automatic vacuum of table \"%s.%s.%s\"",
-                          datname, nspname, relname);
+                          tab->at_datname, tab->at_nspname, tab->at_relname);
            else
                errcontext("automatic analyze of table \"%s.%s.%s\"",
-                          datname, nspname, relname);
+                          tab->at_datname, tab->at_nspname, tab->at_relname);
            EmitErrorReport();
 
            /* this resets the PGPROC flags too */
@@ -2219,10 +2216,14 @@ do_autovacuum(void)
        /* the PGPROC flags are reset at the next end of transaction */
 
        /* be tidy */
+deleted:
+       if (tab->at_datname != NULL)
+           pfree(tab->at_datname);
+       if (tab->at_nspname != NULL)
+           pfree(tab->at_nspname);
+       if (tab->at_relname != NULL)
+           pfree(tab->at_relname);
        pfree(tab);
-       pfree(datname);
-       pfree(nspname);
-       pfree(relname);
 
        /* remove my info from shared memory */
        LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
@@ -2299,6 +2300,8 @@ get_pgstat_tabentry_relid(Oid relid, bool isshared, PgStat_StatDBEntry *shared,
  * Recheck whether a plain table still needs vacuum or analyze; be it because
  * it does directly, or because its TOAST table does.  Return value is a valid
  * autovac_table pointer if it does, NULL otherwise.
+ *
+ * Note that the returned autovac_table does not have the name fields set.
  */
 static autovac_table *
 table_recheck_autovac(Oid relid)
@@ -2437,6 +2440,9 @@ table_recheck_autovac(Oid relid)
        tab->at_vacuum_cost_limit = vac_cost_limit;
        tab->at_vacuum_cost_delay = vac_cost_delay;
        tab->at_wraparound = wraparound || toast_wraparound;
+       tab->at_relname = NULL;
+       tab->at_nspname = NULL;
+       tab->at_datname = NULL;
    }
 
    heap_close(avRel, AccessShareLock);
@@ -2607,8 +2613,7 @@ relation_needs_vacanalyze(Oid relid,
  *     Vacuum and/or analyze the specified table
  */
 static void
-autovacuum_do_vac_analyze(Oid relid, bool dovacuum, bool doanalyze,
-                         int freeze_min_age, bool for_wraparound,
+autovacuum_do_vac_analyze(autovac_table *tab,
                          BufferAccessStrategy bstrategy)
 {
    VacuumStmt  vacstmt;
@@ -2617,18 +2622,18 @@ autovacuum_do_vac_analyze(Oid relid, bool dovacuum, bool doanalyze,
    MemSet(&vacstmt, 0, sizeof(vacstmt));
 
    vacstmt.type = T_VacuumStmt;
-   vacstmt.vacuum = dovacuum;
+   vacstmt.vacuum = tab->at_dovacuum;
    vacstmt.full = false;
-   vacstmt.analyze = doanalyze;
-   vacstmt.freeze_min_age = freeze_min_age;
+   vacstmt.analyze = tab->at_doanalyze;
+   vacstmt.freeze_min_age = tab->at_freeze_min_age;
    vacstmt.verbose = false;
    vacstmt.relation = NULL;    /* not used since we pass a relid */
    vacstmt.va_cols = NIL;
 
    /* Let pgstat know what we're doing */
-   autovac_report_activity(&vacstmt, relid);
+   autovac_report_activity(tab);
 
-   vacuum(&vacstmt, relid, bstrategy, for_wraparound, true);
+   vacuum(&vacstmt, tab->at_relid, bstrategy, tab->at_wraparound, true);
 }
 
 /*
@@ -2643,37 +2648,28 @@ autovacuum_do_vac_analyze(Oid relid, bool dovacuum, bool doanalyze,
  * bother to report "<IDLE>" or some such.
  */
 static void
-autovac_report_activity(VacuumStmt *vacstmt, Oid relid)
+autovac_report_activity(autovac_table *tab)
 {
-   char       *relname = get_rel_name(relid);
-   char       *nspname = get_namespace_name(get_rel_namespace(relid));
-
 #define MAX_AUTOVAC_ACTIV_LEN (NAMEDATALEN * 2 + 32)
-   char        activity[MAX_AUTOVAC_ACTIV_LEN];
+   char    activity[MAX_AUTOVAC_ACTIV_LEN];
+   int     len;
 
    /* Report the command and possible options */
-   if (vacstmt->vacuum)
+   if (tab->at_dovacuum)
        snprintf(activity, MAX_AUTOVAC_ACTIV_LEN,
                 "autovacuum: VACUUM%s",
-                vacstmt->analyze ? " ANALYZE" : "");
+                tab->at_doanalyze ? " ANALYZE" : "");
    else
        snprintf(activity, MAX_AUTOVAC_ACTIV_LEN,
                 "autovacuum: ANALYZE");
 
    /*
     * Report the qualified name of the relation.
-    *
-    * Paranoia is appropriate here in case relation was recently dropped ---
-    * the lsyscache routines we just invoked will return NULL rather than
-    * failing.
     */
-   if (relname && nspname)
-   {
-       int         len = strlen(activity);
+   len = strlen(activity);
 
-       snprintf(activity + len, MAX_AUTOVAC_ACTIV_LEN - len,
-                " %s.%s", nspname, relname);
-   }
+   snprintf(activity + len, MAX_AUTOVAC_ACTIV_LEN - len,
+            " %s.%s", tab->at_nspname, tab->at_relname);
 
    /* Set statement_timestamp() to current time for pg_stat_activity */
    SetCurrentStatementStartTimestamp();