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MDEV-22867 Assertion instant.n_core_fields == n_core_fields failed

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This is a race condition where a table on which a 10.3-style
instant ADD COLUMN is emptied during the execution of
ALTER TABLE ... DROP COLUMN ..., DROP INDEX ..., ALGORITHM=NOCOPY.

In commit 2c4844c9e7 the
function instant_metadata_lock() would prevent this race condition.
But, it would also hold a page latch on the leftmost leaf page of
clustered index for the duration of a possible DROP INDEX operation.

The race could be fixed by restoring the function
instant_metadata_lock() that was removed in
commit ea37b14409
but it would be more future-proof to prevent the
dict_index_t::clear_instant_add() call from being issued at all.

We at some point support DROP COLUMN ..., ADD INDEX ..., ALGORITHM=NOCOPY
and that would spend a non-trivial amount of
execution time in ha_innobase::inplace_alter(),
making a server hang possible. Currently this is not supported
and our added test case will notice when the support is introduced.

dict_index_t::must_avoid_clear_instant_add(): Determine if
a call to clear_instant_add() must be avoided.

btr_discard_only_page_on_level(): Preserve the metadata record
if must_avoid_clear_instant_add() holds.

btr_cur_optimistic_delete_func(), btr_cur_pessimistic_delete():
Do not remove the metadata record even if the table becomes empty
but must_avoid_clear_instant_add() holds.

btr_pcur_store_position(): Relax a debug assertion.

This is joint work with Thirunarayanan Balathandayuthapani.
This commit is contained in:
Marko Mäkelä
2020-06-12 20:30:01 +03:00
parent d7d80689b3
commit 431200090e
6 changed files with 101 additions and 4 deletions
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33
mysql-test/suite/innodb/r/instant_alter_debug.result
View File

@@ -370,3 +370,36 @@ b
SET DEBUG_SYNC='RESET';
disconnect con2;
DROP TABLE t1;
#
# MDEV-22867 Assertion instant.n_core_fields == n_core_fields
# in dict_index_t::instant_add_field
#
CREATE TABLE t1 (a INT PRIMARY KEY, b INT UNIQUE) ENGINE=InnoDB;
INSERT INTO t1 SET a=1;
connect prevent_purge,localhost,root,,;
START TRANSACTION WITH CONSISTENT SNAPSHOT;
connection default;
ALTER TABLE t1 ADD COLUMN c INT;
DELETE FROM t1;
connect con2,localhost,root,,test;
ALTER TABLE t1 DROP b, ADD INDEX(c), ALGORITHM=NOCOPY;
ERROR 0A000: ALGORITHM=NOCOPY is not supported for this operation. Try ALGORITHM=INPLACE
SET DEBUG_SYNC='innodb_inplace_alter_table_enter SIGNAL ddl WAIT_FOR emptied';
ALTER TABLE t1 DROP b;
connection default;
SET DEBUG_SYNC='now WAIT_FOR ddl';
BEGIN;
INSERT INTO t1 SET a=1;
connection prevent_purge;
COMMIT;
disconnect prevent_purge;
connection default;
ROLLBACK;
SELECT * FROM t1;
a b c
SET DEBUG_SYNC='now SIGNAL emptied';
connection con2;
disconnect con2;
connection default;
DROP TABLE t1;
SET DEBUG_SYNC=RESET;