Fix assorted bugs in CREATE/DROP INDEX CONCURRENTLY.

Commit 8cb53654dbdb4c386369eb988062d0bbb6de725e, which introduced DROP
INDEX CONCURRENTLY, managed to break CREATE INDEX CONCURRENTLY via a poor
choice of catalog state representation.  The pg_index state for an index
that's reached the final pre-drop stage was the same as the state for an
index just created by CREATE INDEX CONCURRENTLY.  This meant that the
(necessary) change to make RelationGetIndexList ignore about-to-die indexes
also made it ignore freshly-created indexes; which is catastrophic because
the latter do need to be considered in HOT-safety decisions.  Failure to
do so leads to incorrect index entries and subsequently wrong results from
queries depending on the concurrently-created index.

To fix, add an additional boolean column "indislive" to pg_index, so that
the freshly-created and about-to-die states can be distinguished.  (This
change obviously is only possible in HEAD.  This patch will need to be
back-patched, but in 9.2 we'll use a kluge consisting of overloading the
formerly-impossible state of indisvalid = true and indisready = false.)

In addition, change CREATE/DROP INDEX CONCURRENTLY so that the pg_index
flag changes they make 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.  This is a pre-existing bug in CREATE INDEX
CONCURRENTLY, which was copied into the DROP code.

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.

In addition, do some code and docs review for DROP INDEX CONCURRENTLY;
some cosmetic code cleanup but mostly addition and revision of comments.

This will need to be back-patched, but in a noticeably different form,
so I'm committing it to HEAD before working on the back-patch.

Problem reported by Amit Kapila, diagnosis by Pavan Deolassee,
fix by Tom Lane and Andres Freund.

1 files changed, 12 insertions, 41 deletions

diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index dd46cf93dad..75f9ff19cc7 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -124,6 +124,7 @@ CheckIndexCompatible(Oid oldId,
 	Oid			accessMethodId;
 	Oid			relationId;
 	HeapTuple	tuple;
+	Form_pg_index indexForm;
 	Form_pg_am	accessMethodForm;
 	bool		amcanorder;
 	int16	   *coloptions;
@@ -193,17 +194,22 @@ CheckIndexCompatible(Oid oldId,
 	tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(oldId));
 	if (!HeapTupleIsValid(tuple))
 		elog(ERROR, "cache lookup failed for index %u", oldId);
+	indexForm = (Form_pg_index) GETSTRUCT(tuple);
 
-	/* We don't assess expressions or predicates; assume incompatibility. */
+	/*
+	 * We don't assess expressions or predicates; assume incompatibility.
+	 * Also, if the index is invalid for any reason, treat it as incompatible.
+	 */
 	if (!(heap_attisnull(tuple, Anum_pg_index_indpred) &&
-		  heap_attisnull(tuple, Anum_pg_index_indexprs)))
+		  heap_attisnull(tuple, Anum_pg_index_indexprs) &&
+		  IndexIsValid(indexForm)))
 	{
 		ReleaseSysCache(tuple);
 		return false;
 	}
 
 	/* Any change in operator class or collation breaks compatibility. */
-	old_natts = ((Form_pg_index) GETSTRUCT(tuple))->indnatts;
+	old_natts = indexForm->indnatts;
 	Assert(old_natts == numberOfAttributes);
 
 	d = SysCacheGetAttr(INDEXRELID, tuple, Anum_pg_index_indcollation, &isnull);
@@ -320,9 +326,6 @@ DefineIndex(IndexStmt *stmt,
 	LockRelId	heaprelid;
 	LOCKTAG		heaplocktag;
 	Snapshot	snapshot;
-	Relation	pg_index;
-	HeapTuple	indexTuple;
-	Form_pg_index indexForm;
 	int			i;
 
 	/*
@@ -717,23 +720,7 @@ DefineIndex(IndexStmt *stmt,
 	 * commit this transaction, any new transactions that open the table must
 	 * insert new entries into the index for insertions and non-HOT updates.
 	 */
-	pg_index = heap_open(IndexRelationId, RowExclusiveLock);
-
-	indexTuple = SearchSysCacheCopy1(INDEXRELID,
-									 ObjectIdGetDatum(indexRelationId));
-	if (!HeapTupleIsValid(indexTuple))
-		elog(ERROR, "cache lookup failed for index %u", indexRelationId);
-	indexForm = (Form_pg_index) GETSTRUCT(indexTuple);
-
-	Assert(!indexForm->indisready);
-	Assert(!indexForm->indisvalid);
-
-	indexForm->indisready = true;
-
-	simple_heap_update(pg_index, &indexTuple->t_self, indexTuple);
-	CatalogUpdateIndexes(pg_index, indexTuple);
-
-	heap_close(pg_index, RowExclusiveLock);
+	index_set_state_flags(indexRelationId, INDEX_CREATE_SET_READY);
 
 	/* we can do away with our snapshot */
 	PopActiveSnapshot();
@@ -857,23 +844,7 @@ DefineIndex(IndexStmt *stmt,
 	/*
 	 * Index can now be marked valid -- update its pg_index entry
 	 */
-	pg_index = heap_open(IndexRelationId, RowExclusiveLock);
-
-	indexTuple = SearchSysCacheCopy1(INDEXRELID,
-									 ObjectIdGetDatum(indexRelationId));
-	if (!HeapTupleIsValid(indexTuple))
-		elog(ERROR, "cache lookup failed for index %u", indexRelationId);
-	indexForm = (Form_pg_index) GETSTRUCT(indexTuple);
-
-	Assert(indexForm->indisready);
-	Assert(!indexForm->indisvalid);
-
-	indexForm->indisvalid = true;
-
-	simple_heap_update(pg_index, &indexTuple->t_self, indexTuple);
-	CatalogUpdateIndexes(pg_index, indexTuple);
-
-	heap_close(pg_index, RowExclusiveLock);
+	index_set_state_flags(indexRelationId, INDEX_CREATE_SET_VALID);
 
 	/*
 	 * The pg_index update will cause backends (including this one) to update
@@ -881,7 +852,7 @@ DefineIndex(IndexStmt *stmt,
 	 * relcache inval on the parent table to force replanning of cached plans.
 	 * Otherwise existing sessions might fail to use the new index where it
 	 * would be useful.  (Note that our earlier commits did not create reasons
-	 * to replan; relcache flush on the index itself was sufficient.)
+	 * to replan; so relcache flush on the index itself was sufficient.)
 	 */
 	CacheInvalidateRelcacheByRelid(heaprelid.relId);