Disallow DROP TABLE/DROP INDEX inside a transaction block.

We can't support these properly, since once the relation's physical files
are unlinked, there's no way to roll back the transaction.  I suppose
we could postpone the unlink till transaction commit, but then what of
BEGIN; DROP TABLE foo; CREATE TABLE foo; ?
The code does allow dropping a table/index created in the current
transaction block, however, since the post-abort state would be that
the table doesn't exist anyway.

diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index b571cf3..561cb21 100644 (file)
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/catalog/heap.c,v 1.94 1999/09/04 22:00:29 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/catalog/heap.c,v 1.95 1999/09/05 17:43:47 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -30,6 +30,7 @@
 #include "miscadmin.h"
 
 #include "access/heapam.h"
+#include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/catname.h"
 #include "catalog/heap.h"
@@ -1232,7 +1233,7 @@ heap_destroy_with_catalog(char *relname)
        bool            istemp = (get_temp_rel_by_name(relname) != NULL);
 
        /* ----------------
-        *      first open the relation.  if the relation does exist,
+        *      first open the relation.  if the relation doesn't exist,
         *      heap_openr() returns NULL.
         * ----------------
         */
@@ -1254,6 +1255,17 @@ heap_destroy_with_catalog(char *relname)
                         &rel->rd_rel->relname);
 
        /* ----------------
+        *      We do not allow DROP TABLE within a transaction block, because
+        *      if the transaction is later rolled back there would be no way to
+        *      undo the unlink of the relation's physical file.  The sole exception
+        *      is for relations created in the current transaction, since the post-
+        *      abort state would be that they don't exist anyway.
+        * ----------------
+        */
+       if (IsTransactionBlock() && ! rel->rd_myxactonly)
+               elog(ERROR, "Cannot destroy relation within a transaction block");
+
+       /* ----------------
         *      remove inheritance information
         * ----------------
         */
@@ -1307,17 +1319,10 @@ heap_destroy_with_catalog(char *relname)
         */
        ReleaseRelationBuffers(rel);
 
-       /* ----------------
-        *      flush the relation from the relcache
-        * ----------------
-        * Does nothing!!! Flushing moved below.        - vadim 06/04/97
-       RelationIdInvalidateRelationCacheByRelationId(rel->rd_id);
-        */
-
        RemoveConstraints(rel);
 
        /* ----------------
-        *      unlink the relation and finish up.
+        *      unlink the relation's physical file and finish up.
         * ----------------
         */
        if (!(rel->rd_isnoname) || !(rel->rd_nonameunlinked))
@@ -1329,6 +1334,10 @@ heap_destroy_with_catalog(char *relname)
 
        heap_close(rel);
 
+       /* ----------------
+        *      flush the relation from the relcache
+        * ----------------
+        */
        RelationForgetRelation(rid);
 }
 

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index d52731b..c90c27f 100644 (file)
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/catalog/index.c,v 1.88 1999/09/04 22:00:29 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/catalog/index.c,v 1.89 1999/09/05 17:43:47 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -23,6 +23,7 @@
 #include "access/genam.h"
 #include "access/heapam.h"
 #include "access/istrat.h"
+#include "access/xact.h"
 #include "bootstrap/bootstrap.h"
 #include "catalog/catname.h"
 #include "catalog/heap.h"
@@ -1106,6 +1107,17 @@ index_destroy(Oid indexId)
        userindexRelation = index_open(indexId);
 
        /* ----------------
+        *      We do not allow DROP INDEX within a transaction block, because
+        *      if the transaction is later rolled back there would be no way to
+        *      undo the unlink of the relation's physical file.  The sole exception
+        *      is for relations created in the current transaction, since the post-
+        *      abort state would be that they don't exist anyway.
+        * ----------------
+        */
+       if (IsTransactionBlock() && ! userindexRelation->rd_myxactonly)
+               elog(ERROR, "Cannot destroy index within a transaction block");
+
+       /* ----------------
         * fix RELATION relation
         * ----------------
         */
@@ -1164,7 +1176,7 @@ index_destroy(Oid indexId)
        ReleaseRelationBuffers(userindexRelation);
 
        if (smgrunlink(DEFAULT_SMGR, userindexRelation) != SM_SUCCESS)
-               elog(ERROR, "amdestroyr: unlink: %m");
+               elog(ERROR, "index_destroy: unlink: %m");
 
        index_close(userindexRelation);
        RelationForgetRelation(RelationGetRelid(userindexRelation));