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Fix longstanding problems in VACUUM caused by untimely interruptions
authorAlvaro Herrera <alvherre@alvh.no-ip.org>
Tue, 10 Nov 2009 18:01:46 +0000 (18:01 +0000)
committerAlvaro Herrera <alvherre@alvh.no-ip.org>
Tue, 10 Nov 2009 18:01:46 +0000 (18:01 +0000)
In VACUUM FULL, an interrupt after the initial transaction has been recorded
as committed can cause postmaster to restart with the following error message:
PANIC: cannot abort transaction NNNN, it was already committed
This problem has been reported many times.

In lazy VACUUM, an interrupt after the table has been truncated by
lazy_truncate_heap causes other backends' relcache to still point to the
removed pages; this can cause future INSERT and UPDATE queries to error out
with the following error message:
could not read block XX of relation 1663/NNN/MMMM: read only 0 of 8192 bytes
The window to this race condition is extremely narrow, but it has been seen in
the wild involving a cancelled autovacuum process.

The solution for both problems is to inhibit interrupts in both operations
until after the respective transactions have been committed.  It's not a
complete solution, because the transaction could theoretically be aborted by
some other error, but at least fixes the most common causes of both problems.

src/backend/commands/vacuum.c patch | blob | blame | history
src/backend/commands/vacuumlazy.c patch | blob | blame | history
src/include/commands/vacuum.h patch | blob | blame | history

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 84a654799c54f11db1f889c01c6a422882579983..afb2ad75164d50d6dd240596adfcd42aee74d4e4 100644 (file)
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.263.2.5 2008/02/11 19:15:00 tgl Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.263.2.6 2009/11/10 18:01:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -114,10 +114,10 @@ static void vac_update_dbstats(Oid dbid,
 static void vac_truncate_clog(TransactionId vacuumXID,
                  TransactionId frozenXID);
 static bool vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind);
-static void full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
+static bool full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
 static void scan_heap(VRelStats *vacrelstats, Relation onerel,
          VacPageList vacuum_pages, VacPageList fraged_pages);
-static void repair_frag(VRelStats *vacrelstats, Relation onerel,
+static bool repair_frag(VRelStats *vacrelstats, Relation onerel,
            VacPageList vacuum_pages, VacPageList fraged_pages,
            int nindexes, Relation *Irel);
 static void vacuum_heap(VRelStats *vacrelstats, Relation onerel,
@@ -744,6 +744,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
    bool        result;
    AclId       save_userid;
    bool        save_secdefcxt;
+   bool        heldoff;
 
    /* Begin a transaction for vacuuming this relation */
    StartTransactionCommand();
@@ -860,9 +861,9 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
     * Do the actual work --- either FULL or "lazy" vacuum
     */
    if (vacstmt->full)
-       full_vacuum_rel(onerel, vacstmt);
+       heldoff = full_vacuum_rel(onerel, vacstmt);
    else
-       lazy_vacuum_rel(onerel, vacstmt);
+       heldoff = lazy_vacuum_rel(onerel, vacstmt);
 
    result = true;              /* did the vacuum */
 
@@ -877,6 +878,10 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
     */
    CommitTransactionCommand();
 
+   /* now we can allow interrupts again, if disabled */
+   if (heldoff)
+       RESUME_INTERRUPTS();
+
    /*
     * If the relation has a secondary toast rel, vacuum that too while we
     * still hold the session lock on the master table.  Note however that
@@ -915,8 +920,11 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
  *
  *     At entry, we have already established a transaction and opened
  *     and locked the relation.
+ *
+ *     The return value indicates whether this function has held off
+ *     interrupts -- caller must RESUME_INTERRUPTS() after commit if true.
  */
-static void
+static bool
 full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 {
    VacPageListData vacuum_pages;       /* List of pages to vacuum and/or
@@ -927,6 +935,7 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
    int         nindexes,
                i;
    VRelStats  *vacrelstats;
+   bool        heldoff = false;
 
    vacuum_set_xid_limits(vacstmt, onerel->rd_rel->relisshared,
                          &OldestXmin, &FreezeLimit);
@@ -968,8 +977,8 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
    if (fraged_pages.num_pages > 0)
    {
        /* Try to shrink heap */
-       repair_frag(vacrelstats, onerel, &vacuum_pages, &fraged_pages,
-                   nindexes, Irel);
+       heldoff = repair_frag(vacrelstats, onerel, &vacuum_pages, &fraged_pages,
+                             nindexes, Irel);
        vac_close_indexes(nindexes, Irel);
    }
    else
@@ -1000,6 +1009,8 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
    /* update statistics in pg_class */
    vac_update_relstats(RelationGetRelid(onerel), vacrelstats->rel_pages,
                        vacrelstats->rel_tuples, vacrelstats->hasindex);
+
+   return heldoff;
 }
 
 
@@ -1412,8 +1423,11 @@ scan_heap(VRelStats *vacrelstats, Relation onerel,
  *     for them after committing (in hack-manner - without losing locks
  *     and freeing memory!) current transaction. It truncates relation
  *     if some end-blocks are gone away.
+ *
+ *     The return value indicates whether this function has held off
+ *     interrupts -- caller must RESUME_INTERRUPTS() after commit if true.
  */
-static void
+static bool
 repair_frag(VRelStats *vacrelstats, Relation onerel,
            VacPageList vacuum_pages, VacPageList fraged_pages,
            int nindexes, Relation *Irel)
@@ -1459,6 +1473,7 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
                dowrite,
                chain_tuple_moved;
    VacRUsage   ru0;
+   bool        heldoff = false;
 
    vac_init_rusage(&ru0);
 
@@ -2358,7 +2373,13 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
         * a lot of extra code to close and re-open the relation, indexes,
         * etc.  For now, a quick hack: record status of current
         * transaction as committed, and continue.
+        *
+        * We prevent cancel interrupts after this point to mitigate the
+        * problem that you can't abort the transaction now; caller is
+        * responsible for re-enabling them after committing the transaction.
         */
+       HOLD_INTERRUPTS();
+       heldoff = true;
        RecordTransactionCommit();
    }
 
@@ -2591,6 +2612,8 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
    ExecCloseIndices(resultRelInfo);
 
    FreeExecutorState(estate);
+
+   return heldoff;
 }
 
 /*
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index d7daf1ba3c93af85993b96977a4853c06fe7d25f..724f9ec46c41d25b87f02d7cc9d3a500487781d0 100644 (file)
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -31,7 +31,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/commands/vacuumlazy.c,v 1.32.2.3 2009/01/06 14:56:13 heikki Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/commands/vacuumlazy.c,v 1.32.2.4 2009/11/10 18:01:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -120,8 +120,11 @@ static int vac_cmp_page_spaces(const void *left, const void *right);
  *
  *     At entry, we have already established a transaction and opened
  *     and locked the relation.
+ *
+ *     The return value indicates whether this function has held off
+ *     interrupts -- caller must RESUME_INTERRUPTS() after commit if true.
  */
-void
+bool
 lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 {
    LVRelStats *vacrelstats;
@@ -129,6 +132,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
    int         nindexes;
    bool        hasindex;
    BlockNumber possibly_freeable;
+   bool        heldoff = false;
 
    if (vacstmt->verbose)
        elevel = INFO;
@@ -159,12 +163,22 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
     *
     * Don't even think about it unless we have a shot at releasing a goodly
     * number of pages.  Otherwise, the time taken isn't worth it.
+    *
+    * Note that after we've truncated the heap, it's too late to abort the
+    * transaction; doing so would lose the sinval messages needed to tell the
+    * other backends about the table being shrunk.  We prevent interrupts in
+    * that case; caller is responsible for re-enabling them after
+    * committing the transaction.
     */
    possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages;
    if (possibly_freeable > 0 &&
        (possibly_freeable >= REL_TRUNCATE_MINIMUM ||
         possibly_freeable >= vacrelstats->rel_pages / REL_TRUNCATE_FRACTION))
+   {
+       HOLD_INTERRUPTS();
+       heldoff = true;
        lazy_truncate_heap(onerel, vacrelstats);
+   }
 
    /* Update shared free space map with final free space info */
    lazy_update_fsm(onerel, vacrelstats);
@@ -172,6 +186,8 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
    /* Update statistics in pg_class */
    vac_update_relstats(RelationGetRelid(onerel), vacrelstats->rel_pages,
                        vacrelstats->rel_tuples, hasindex);
+
+   return heldoff;
 }
 
 
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index 194adb17c8aad9ab8f6c8f0c970ed7826f31de26..99dd9c0c9b23f7f1f2578f535bb4aabb8efdccb7 100644 (file)
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: vacuum.h,v 1.46 2003/08/04 02:40:13 momjian Exp $
+ * $Id: vacuum.h,v 1.46.4.1 2009/11/10 18:01:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -55,7 +55,7 @@ extern void vac_init_rusage(VacRUsage *ru0);
 extern const char *vac_show_rusage(VacRUsage *ru0);
 
 /* in commands/vacuumlazy.c */
-extern void lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
+extern bool lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
 
 /* in commands/analyze.c */
 extern void analyze_rel(Oid relid, VacuumStmt *vacstmt);
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