Hi
On 08/04/2026 11:17, Soumya S Murali wrote:
> I worked on the issue of accessing temporary tables belonging to other
> sessions and tried implementing the fix at the buffer manager level,
> as suggested. I added checks in ReadBuffer_common() and
> PrefetchBuffer() to reject access when a relation is temporary
> (relpersistence = TEMP) but does not use local buffers
> (!RelationUsesLocalBuffers) so that it ensures only heap page access
> is blocked, while catalog lookups and other metadata operations
> continue to work as before. While testing, I observed that in many
> cases the query does not reach the buffer manager because name
> resolution fails earlier with “relation does not exist”. However, the
> added checks ensure that even if execution reaches the buffer layer,
> access to other sessions’ temporary tables is safely rejected. The
> change is minimal, and did not modify parser/ACL behavior and all
> regression tests got passed successfully too.
> Kindly review the attached patch herewith. Please let me know if this
> approach aligns with expectations or if further adjustments are
> needed.
A few comments:
== PrefetchBuffer ==
The condition nested inside the if (RelationUsesLocalBuffers(reln))
tests the opposite of the main if !RelationUsesLocalBuffers(reln):
if (RelationUsesLocalBuffers(reln))
{
/* ACCESS DENIED CHECK */
if (reln != NULL &&
reln->rd_rel != NULL &&
reln->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
!RelationUsesLocalBuffers(reln))
{
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
}
...
}
So it'll be always false, making the ereport unreachable.
== ReadBufferExtended ==
These conditions cancel each other out:
if (reln->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
!RelationUsesLocalBuffers(reln))
RelationUsesLocalBuffers(reln) expands to
((relation)->rd_rel->relpersistence == RELPERSISTENCE_TEMP), making the
error message unreachable. Perhaps you meant RELATION_IS_OTHER_TEMP?
== ReadBuffer_common ==
Same as in ReadBufferExtended and PrefetchBuffer.
== tests ==
You excluded the tests from the patch.
== patch version ==
You forgot to add the patch version.
Best, Jim
