From 5ed281e21d363aa1661587c331a022d7e6763d0c Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sun, 23 Sep 2018 16:05:45 -0400 Subject: Fix failure in WHERE CURRENT OF after rewinding the referenced cursor. In a case where we have multiple relation-scan nodes in a cursor plan, such as a scan of an inheritance tree, it's possible to fetch from a given scan node, then rewind the cursor and fetch some row from an earlier scan node. In such a case, execCurrent.c mistakenly thought that the later scan node was still active, because ExecReScan hadn't done anything to make it look not-active. We'd get some sort of failure in the case of a SeqScan node, because the node's scan tuple slot would be pointing at a HeapTuple whose t_self gets reset to invalid by heapam.c. But it seems possible that for other relation scan node types we'd actually return a valid tuple TID to the caller, resulting in updating or deleting a tuple that shouldn't have been considered current. To fix, forcibly clear the ScanTupleSlot in ExecScanReScan. Another issue here, which seems only latent at the moment but could easily become a live bug in future, is that rewinding a cursor does not necessarily lead to *immediately* applying ExecReScan to every scan-level node in the plan tree. Upper-level nodes will think that they can postpone that call if their child node is already marked with chgParam flags. I don't see a way for that to happen today in a plan tree that's simple enough for execCurrent.c's search_plan_tree to understand, but that's one heck of a fragile assumption. So, add some logic in search_plan_tree to detect chgParam flags being set on nodes that it descended to/through, and assume that that means we should consider lower scan nodes to be logically reset even if their ReScan call hasn't actually happened yet. Per bug #15395 from Matvey Arye. This has been broken for a long time, so back-patch to all supported branches. Discussion: https://postgr.es/m/153764171023.14986.280404050547008575@wrigleys.postgresql.org --- src/test/regress/sql/portals.sql | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'src/test/regress/sql/portals.sql') diff --git a/src/test/regress/sql/portals.sql b/src/test/regress/sql/portals.sql index d1a589094ea..52560ac0275 100644 --- a/src/test/regress/sql/portals.sql +++ b/src/test/regress/sql/portals.sql @@ -472,6 +472,30 @@ DELETE FROM onek WHERE CURRENT OF c1; SELECT stringu1 FROM onek WHERE stringu1 = 'DZAAAA'; ROLLBACK; +-- Check behavior with rewinding to a previous child scan node, +-- as per bug #15395 +BEGIN; +CREATE TABLE current_check (currentid int, payload text); +CREATE TABLE current_check_1 () INHERITS (current_check); +CREATE TABLE current_check_2 () INHERITS (current_check); +INSERT INTO current_check_1 SELECT i, 'p' || i FROM generate_series(1,9) i; +INSERT INTO current_check_2 SELECT i, 'P' || i FROM generate_series(10,19) i; + +DECLARE c1 SCROLL CURSOR FOR SELECT * FROM current_check; + +-- This tests the fetch-backwards code path +FETCH ABSOLUTE 12 FROM c1; +FETCH ABSOLUTE 8 FROM c1; +DELETE FROM current_check WHERE CURRENT OF c1 RETURNING *; + +-- This tests the ExecutorRewind code path +FETCH ABSOLUTE 13 FROM c1; +FETCH ABSOLUTE 1 FROM c1; +DELETE FROM current_check WHERE CURRENT OF c1 RETURNING *; + +SELECT * FROM current_check; +ROLLBACK; + -- Make sure snapshot management works okay, per bug report in -- 235395b90909301035v7228ce63q392931f15aa74b31@mail.gmail.com BEGIN; -- cgit v1.2.3