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Fix heap_getattr() handling of fast defaults.

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Previously heap_getattr() returned NULL for attributes with a fast
default value (c.f. 16828d5c02), as it had no handling whatsoever
for that case.

A previous fix, 7636e5c60f, attempted to fix issues caused by this
oversight, but just expanding OLD tuples for triggers doesn't actually
solve the underlying issue.

One known consequence of this bug is that the check for HOT updates
can return the wrong result, when a previously fast-default'ed column
is set to NULL. Which in turn means that an index over a column with
fast default'ed columns might be corrupt if the underlying column(s)
allow NULLs.

Fix by handling fast default columns in heap_getattr(), remove now
superfluous expansion in GetTupleForTrigger().

Author: Andres Freund
Discussion: https://postgr.es/m/20190201162404.onngi77f26baem4g@alap3.anarazel.de
Backpatch: 11, where fast defaults were introduced
This commit is contained in:
Andres Freund
2019-02-06 01:09:32 -08:00
parent d07fb6810e
commit 171e0418b0
5 changed files with 52 additions and 11 deletions
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27
src/test/regress/expected/fast_default.out
View File

@ -770,6 +770,33 @@ SELECT * FROM vtype2;
2 | yyy
(2 rows)
-- Ensure that defaults are checked when evaluating whether HOT update
-- is possible, this was broken for a while:
-- https://postgr.es/m/20190202133521.ylauh3ckqa7colzj%40alap3.anarazel.de
BEGIN;
CREATE TABLE t();
INSERT INTO t DEFAULT VALUES;
ALTER TABLE t ADD COLUMN a int DEFAULT 1;
CREATE INDEX ON t(a);
-- set column with a default 1 to NULL, due to a bug that wasn't
-- noticed has heap_getattr buggily returned NULL for default columns
UPDATE t SET a = NULL;
-- verify that index and non-index scans show the same result
SET LOCAL enable_seqscan = true;
SELECT * FROM t WHERE a IS NULL;
a
---
(1 row)
SET LOCAL enable_seqscan = false;
SELECT * FROM t WHERE a IS NULL;
a
---
(1 row)
ROLLBACK;
-- cleanup
DROP TABLE vtype;
DROP TABLE vtype2;

20
src/test/regress/sql/fast_default.sql
View File

@ -505,6 +505,26 @@ ALTER TABLE vtype2 ALTER COLUMN b TYPE varchar(20) USING b::varchar(20);
SELECT * FROM vtype2;
-- Ensure that defaults are checked when evaluating whether HOT update
-- is possible, this was broken for a while:
-- https://postgr.es/m/20190202133521.ylauh3ckqa7colzj%40alap3.anarazel.de
BEGIN;
CREATE TABLE t();
INSERT INTO t DEFAULT VALUES;
ALTER TABLE t ADD COLUMN a int DEFAULT 1;
CREATE INDEX ON t(a);
-- set column with a default 1 to NULL, due to a bug that wasn't
-- noticed has heap_getattr buggily returned NULL for default columns
UPDATE t SET a = NULL;
-- verify that index and non-index scans show the same result
SET LOCAL enable_seqscan = true;
SELECT * FROM t WHERE a IS NULL;
SET LOCAL enable_seqscan = false;
SELECT * FROM t WHERE a IS NULL;
ROLLBACK;
-- cleanup
DROP TABLE vtype;
DROP TABLE vtype2;