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();