In session 1:
regression=# create temp table tt(f1 int);
CREATE TABLE
regression=# insert into tt values(44);
INSERT 0 1
regression=# \d tt
Table "pg_temp_77.tt"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
f1 | integer | | |
In session 2:
regression=# select * from pg_temp_77.tt; -- use the schema shown in session 1
f1
----
(0 rows)
Branches before 17 show the expected failure
ERROR: cannot access temporary tables of other sessions
but that's gone missing :-(. Apparently, we refactored things enough
that ReadBufferExtended is not used for a simple seqscan, and since
that's where the check for an other-session temp table is, we get
no error and instead bogus results. I did not bother to bisect to
find a culprit commit, but given that the failure manifests in 17,
I'm betting the stream I/O stuff is at fault.
I experimented with moving the check into PinBufferForBlock, and
that seems to work correctly, but I wonder if someone who's messed
with this code more recently than I would prefer a different
solution.
regards, tom lane
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index fe470de63f2..e27d74a24c2 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -655,7 +655,7 @@ PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
if (RelationUsesLocalBuffers(reln))
{
- /* see comments in ReadBufferExtended */
+ /* see comments in PinBufferForBlock */
if (RELATION_IS_OTHER_TEMP(reln))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -807,16 +807,6 @@ ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
{
Buffer buf;
- /*
- * Reject attempts to read non-local temporary relations; we would be
- * likely to get wrong data since we have no visibility into the owning
- * session's local buffers.
- */
- if (RELATION_IS_OTHER_TEMP(reln))
- ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("cannot access temporary tables of other sessions")));
-
/*
* Read the buffer, and update pgstat counters to reflect a cache hit or
* miss.
@@ -1128,6 +1118,18 @@ PinBufferForBlock(Relation rel,
if (persistence == RELPERSISTENCE_TEMP)
{
+ /*
+ * Reject attempts to read non-local temporary relations; we would be
+ * likely to get wrong data since we have no visibility into the
+ * owning session's local buffers. We don't expect to get here
+ * without a relcache entry (see ReadBufferWithoutRelcache).
+ */
+ Assert(rel);
+ if (RELATION_IS_OTHER_TEMP(rel))
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("cannot access temporary tables of other sessions")));
+
io_context = IOCONTEXT_NORMAL;
io_object = IOOBJECT_TEMP_RELATION;
}
