Fix assorted bugs in CREATE INDEX CONCURRENTLY.

This patch changes CREATE INDEX CONCURRENTLY so that the pg_index
flag changes it makes without exclusive lock on the index are made via
heap_inplace_update() rather than a normal transactional update.  The
latter is not very safe because moving the pg_index tuple could result in
concurrent SnapshotNow scans finding it twice or not at all, thus possibly
resulting in index corruption.

In addition, fix various places in the code that ought to check to make
sure that the indexes they are manipulating are valid and/or ready as
appropriate.  These represent bugs that have existed since 8.2, since
a failed CREATE INDEX CONCURRENTLY could leave a corrupt or invalid
index behind, and we ought not try to do anything that might fail with
such an index.

Also fix RelationReloadIndexInfo to ensure it copies all the pg_index
columns that are allowed to change after initial creation.  Previously we
could have been left with stale values of some fields in an index relcache
entry.  It's not clear whether this actually had any user-visible
consequences, but it's at least a bug waiting to happen.

This is a subset of a patch already applied in 9.2 and HEAD.  Back-patch
into all earlier supported branches.

Tom Lane and Andres Freund

1 files changed, 9 insertions, 1 deletions

diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 5dec4298e2c..81e72825269 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -454,7 +454,7 @@ check_index_is_clusterable(Relation OldHeap, Oid indexOid, bool recheck, LOCKMOD
 	 * might put recently-dead tuples out-of-order in the new table, and there
 	 * is little harm in that.)
 	 */
-	if (!OldIndex->rd_index->indisvalid)
+	if (!IndexIsValid(OldIndex->rd_index))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("cannot cluster on invalid index \"%s\"",
@@ -468,6 +468,11 @@ check_index_is_clusterable(Relation OldHeap, Oid indexOid, bool recheck, LOCKMOD
  * mark_index_clustered: mark the specified index as the one clustered on
  *
  * With indexOid == InvalidOid, will mark all indexes of rel not-clustered.
+ *
+ * Note: we do transactional updates of the pg_index rows, which are unsafe
+ * against concurrent SnapshotNow scans of pg_index.  Therefore this is unsafe
+ * to execute with less than full exclusive lock on the parent table;
+ * otherwise concurrent executions of RelationGetIndexList could miss indexes.
  */
 void
 mark_index_clustered(Relation rel, Oid indexOid)
@@ -523,6 +528,9 @@ mark_index_clustered(Relation rel, Oid indexOid)
 		}
 		else if (thisIndexOid == indexOid)
 		{
+			/* this was checked earlier, but let's be real sure */
+			if (!IndexIsValid(indexForm))
+				elog(ERROR, "cannot cluster on invalid index %u", indexOid);
 			indexForm->indisclustered = true;
 			simple_heap_update(pg_index, &indexTuple->t_self, indexTuple);
 			CatalogUpdateIndexes(pg_index, indexTuple);