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, 23 insertions, 7 deletions

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 606e782ba98..76756dd1d1f 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -1071,9 +1071,16 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound)
 
 
 /*
- * Open all the indexes of the given relation, obtaining the specified kind
- * of lock on each.  Return an array of Relation pointers for the indexes
- * into *Irel, and the number of indexes into *nindexes.
+ * Open all the vacuumable indexes of the given relation, obtaining the
+ * specified kind of lock on each.	Return an array of Relation pointers for
+ * the indexes into *Irel, and the number of indexes into *nindexes.
+ *
+ * We consider an index vacuumable if it is marked insertable (IndexIsReady).
+ * If it isn't, probably a CREATE INDEX CONCURRENTLY command failed early in
+ * execution, and what we have is too corrupt to be processable.  We will
+ * vacuum even if the index isn't indisvalid; this is important because in a
+ * unique index, uniqueness checks will be performed anyway and had better not
+ * hit dangling index pointers.
  */
 void
 vac_open_indexes(Relation relation, LOCKMODE lockmode,
@@ -1087,21 +1094,30 @@ vac_open_indexes(Relation relation, LOCKMODE lockmode,
 
 	indexoidlist = RelationGetIndexList(relation);
 
-	*nindexes = list_length(indexoidlist);
+	/* allocate enough memory for all indexes */
+	i = list_length(indexoidlist);
 
-	if (*nindexes > 0)
-		*Irel = (Relation *) palloc(*nindexes * sizeof(Relation));
+	if (i > 0)
+		*Irel = (Relation *) palloc(i * sizeof(Relation));
 	else
 		*Irel = NULL;
 
+	/* collect just the ready indexes */
 	i = 0;
 	foreach(indexoidscan, indexoidlist)
 	{
 		Oid			indexoid = lfirst_oid(indexoidscan);
+		Relation	indrel;
 
-		(*Irel)[i++] = index_open(indexoid, lockmode);
+		indrel = index_open(indexoid, lockmode);
+		if (IndexIsReady(indrel->rd_index))
+			(*Irel)[i++] = indrel;
+		else
+			index_close(indrel, lockmode);
 	}
 
+	*nindexes = i;
+
 	list_free(indexoidlist);
 }