Avoid crashing when we have problems unlinking files post-commit.

smgrdounlink takes care to not throw an ERROR if it fails to unlink
something, but that caution was rendered useless by commit
3396000684b41e7e9467d1abc67152b39e697035, which put an smgrexists call in
front of it; smgrexists *does* throw error if anything looks funny, such
as getting a permissions error from trying to open the file.  If that
happens post-commit, you get a PANIC, and what's worse the same logic
appears in the WAL replay code, so the database even fails to restart.

Restore the intended behavior by removing the smgrexists call --- it isn't
accomplishing anything that we can't do better by adjusting mdunlink's
ideas of whether it ought to warn about ENOENT or not.

Per report from Joseph Shraibman of unrecoverable crash after trying to
drop a table whose FSM fork had somehow gotten chmod'd to 000 permissions.
Backpatch to 8.4, where the bogus coding was introduced.

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 4691c7e14ab8ec1635e5331e94cc2b46b24e4a32..af75f69dfc0a29456d16e1cdb56aa8decf733ac7 100644 (file)
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1325,8 +1325,7 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 
                for (fork = 0; fork <= MAX_FORKNUM; fork++)
                {
-                       if (smgrexists(srel, fork))
-                               smgrdounlink(srel, fork, false, false);
+                       smgrdounlink(srel, fork, false, false);
                }
                smgrclose(srel);
        }

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 8436deaa1f507739f582ff0fd624eb2110b31cbb..750725a43af15785e05e252eb24a911539b6c568 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -4479,11 +4479,8 @@ xact_redo_commit(xl_xact_commit *xlrec, TransactionId xid, XLogRecPtr lsn)
 
                for (fork = 0; fork <= MAX_FORKNUM; fork++)
                {
-                       if (smgrexists(srel, fork))
-                       {
-                               XLogDropRelation(xlrec->xnodes[i], fork);
-                               smgrdounlink(srel, fork, false, true);
-                       }
+                       XLogDropRelation(xlrec->xnodes[i], fork);
+                       smgrdounlink(srel, fork, false, true);
                }
                smgrclose(srel);
        }
@@ -4584,11 +4581,8 @@ xact_redo_abort(xl_xact_abort *xlrec, TransactionId xid)
 
                for (fork = 0; fork <= MAX_FORKNUM; fork++)
                {
-                       if (smgrexists(srel, fork))
-                       {
-                               XLogDropRelation(xlrec->xnodes[i], fork);
-                               smgrdounlink(srel, fork, false, true);
-                       }
+                       XLogDropRelation(xlrec->xnodes[i], fork);
+                       smgrdounlink(srel, fork, false, true);
                }
                smgrclose(srel);
        }

diff --git a/src/backend/catalog/storage.c b/src/backend/catalog/storage.c
index 2165341e0e172bb5d2c7114e60caba99677cb197..0f99516a6948631528194bce97f978a651d5a935 100644 (file)
--- a/src/backend/catalog/storage.c
+++ b/src/backend/catalog/storage.c
@@ -325,11 +325,10 @@ smgrDoPendingDeletes(bool isCommit)
                                srel = smgropen(pending->relnode);
                                for (i = 0; i <= MAX_FORKNUM; i++)
                                {
-                                       if (smgrexists(srel, i))
-                                               smgrdounlink(srel,
-                                                                        i,
-                                                                        pending->isTemp,
-                                                                        false);
+                                       smgrdounlink(srel,
+                                                                i,
+                                                                pending->isTemp,
+                                                                false);
                                }
                                smgrclose(srel);
                        }

diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index eb5c73d6f8d34f878357a4e3613d6c9e4a0788e9..5458cbdda424760e3caec460659a8815e4ee903b 100644 (file)
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -312,7 +312,13 @@ mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
  * number until it's safe, because relfilenode assignment skips over any
  * existing file.
  *
- * If isRedo is true, it's okay for the relation to be already gone.
+ * All the above applies only to the relation's main fork; other forks can
+ * just be removed immediately, since they are not needed to prevent the
+ * relfilenode number from being recycled.  Also, we do not carefully
+ * track whether other forks have been created or not, but just attempt to
+ * unlink them unconditionally; so we should never complain about ENOENT.
+ *
+ * If isRedo is true, it's unsurprising for the relation to be already gone.
  * Also, we should remove the file immediately instead of queuing a request
  * for later, since during redo there's no possibility of creating a
  * conflicting relation.
@@ -340,13 +346,10 @@ mdunlink(RelFileNode rnode, ForkNumber forkNum, bool isRedo)
        if (isRedo || forkNum != MAIN_FORKNUM)
        {
                ret = unlink(path);
-               if (ret < 0)
-               {
-                       if (!isRedo || errno != ENOENT)
-                               ereport(WARNING,
-                                               (errcode_for_file_access(),
-                                                errmsg("could not remove file \"%s\": %m", path)));
-               }
+               if (ret < 0 && errno != ENOENT)
+                       ereport(WARNING,
+                                       (errcode_for_file_access(),
+                                        errmsg("could not remove file \"%s\": %m", path)));
        }
        else
        {
@@ -369,6 +372,9 @@ mdunlink(RelFileNode rnode, ForkNumber forkNum, bool isRedo)
                        ereport(WARNING,
                                        (errcode_for_file_access(),
                                         errmsg("could not truncate file \"%s\": %m", path)));
+
+               /* Register request to unlink first segment later */
+               register_unlink(rnode);
        }
 
        /*
@@ -400,10 +406,6 @@ mdunlink(RelFileNode rnode, ForkNumber forkNum, bool isRedo)
        }
 
        pfree(path);
-
-       /* Register request to unlink first segment later */
-       if (!isRedo && forkNum == MAIN_FORKNUM)
-               register_unlink(rnode);
 }
 
 /*