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Relax overly strict assertion 

Ever since its birth, ReorderBufferBuildTupleCidHash() has contained an
assertion that a catalog tuple cannot change Cmax after acquiring one.  But
that's wrong: if a subtransaction executes DDL that affects that catalog
tuple, and later aborts and another DDL affects the same tuple, it will
change Cmax.  Relax the assertion to merely verify that the Cmax remains
valid and monotonically increasing, instead.

Add a test that tickles the relevant code.

Diagnosed by, and initial patch submitted by: Arseny Sher
Co-authored-by: Arseny Sher
Discussion: https://postgr.es/m/874l9p8hyw.fsf@ars-thinkpad
This commit is contained in:
Alvaro Herrera 2019-02-12 18:42:37 -03:00
parent a4c6a73aa4
commit c2e0954be3
3 changed files with 40 additions and 5 deletions
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18
contrib/test_decoding/expected/ddl.out
View File

@ -409,6 +409,24 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
COMMIT
(6 rows)
-- check that DDL in aborted subtransactions handled correctly
CREATE TABLE tr_sub_ddl(data int);
BEGIN;
SAVEPOINT a;
ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
INSERT INTO tr_sub_ddl VALUES ('blah-blah');
ROLLBACK TO SAVEPOINT a;
ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
INSERT INTO tr_sub_ddl VALUES(43);
COMMIT;
SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
data
--------------------------------------------------
BEGIN
table public.tr_sub_ddl: INSERT: data[bigint]:43
COMMIT
(3 rows)
/*
* Check whether treating a table as a catalog table works somewhat
*/

13
contrib/test_decoding/sql/ddl.sql
View File

@ -234,6 +234,19 @@ INSERT INTO tr_sub(path) VALUES ('5-top-1-#1');
COMMIT;
SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
-- check that DDL in aborted subtransactions handled correctly
CREATE TABLE tr_sub_ddl(data int);
BEGIN;
SAVEPOINT a;
ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
INSERT INTO tr_sub_ddl VALUES ('blah-blah');
ROLLBACK TO SAVEPOINT a;
ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
INSERT INTO tr_sub_ddl VALUES(43);
COMMIT;
SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');

14
src/backend/replication/logical/reorderbuffer.c
View File

@ -1326,15 +1326,19 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
}
else
{
/*
* Maybe we already saw this tuple before in this transaction,
* but if so it must have the same cmin.
*/
Assert(ent->cmin == change->data.tuplecid.cmin);
Assert(ent->cmax == InvalidCommandId ||
ent->cmax == change->data.tuplecid.cmax);
/*
* if the tuple got valid in this transaction and now got deleted
* we already have a valid cmin stored. The cmax will be
* InvalidCommandId though.
* cmax may be initially invalid, but once set it can only grow,
* and never become invalid again.
*/
Assert((ent->cmax == InvalidCommandId) ||
((change->data.tuplecid.cmax != InvalidCommandId) &&
(change->data.tuplecid.cmax > ent->cmax)));
ent->cmax = change->data.tuplecid.cmax;
}
}