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Strange behavior of DDL with FTWRL

Description

In presence of FTWRL DDL and DML behave differently. DDL shows a strange behavior, seemingly breaking TOI promise.

Session #1:

FLUSH TABLES WITH READ LOCK;

Session #2:

CREATE TABLE IF NOT EXISTS t1 (id int auto_increment primary key);

Observer:

SHOW PROCESSLIST; +----+-------------+-----------+------+---------+------+----------------------+-------------------------------------------------------------------+-----------+---------------+ | Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | +----+-------------+-----------+------+---------+------+----------------------+-------------------------------------------------------------------+-----------+---------------+ | 1 | system user | | NULL | Sleep | 194 | wsrep: aborter idle | NULL | 0 | 0 | | 2 | system user | | NULL | Sleep | 194 | wsrep: applier idle | NULL | 0 | 0 | | 4 | system user | | NULL | Sleep | 192 | wsrep: applier idle | NULL | 0 | 0 | | 5 | msandbox | localhost | NULL | Sleep | 12 | | NULL | 0 | 0 | | 6 | msandbox | localhost | test | Query | 5 | checking permissions | CREATE TABLE IF NOT EXISTS t1 (id int auto_increment primary key) | 0 | 0 | | 7 | msandbox | localhost | NULL | Query | 0 | starting | show processlist | 0 | 0 | +----+-------------+-----------+------+---------+------+----------------------+-------------------------------------------------------------------+-----------+---------------+

On another node at the same time, the table is present already, and writes can be done to it. On the "FTWRL node" table is not present.

FTWRL node:

SELECT * FROM test.t1; ERROR 1146 (42S02): Table 'test.t1' doesn't exist

Another node:

INSERT INTO t1 VALUES (DEFAULT); INSERT INTO t1 VALUES (DEFAULT); SELECT * FROM test.t1; +----+ | id | +----+ | 3 | | 6 | +----+

If wsrep_sync_wait is enabled, reads stall on the "FTWRL node" as well.

Once UNLOCK TABLES; is executed, or Session #1 is terminated, the DDL goes through.

This is probably expected since upon running FTWRL the node will desync, but:
1. DDL is replicated to other nodes and they can write to new table (and other tables)
2. "checking permissions" state is a bit confusing

Comparing with the behavior of FTWRL and DML:
1. DML is not replicated to other nodes
2. DML shows "Waiting for global read lock" state while waiting

Attached "FTWRL node" error log + pt-pmp outputs.

Environment

None

Attachments

3
  • 31 Mar 2020, 01:12 PM
  • 31 Mar 2020, 01:12 PM
  • 31 Mar 2020, 01:12 PM

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Kathy Williamson April 7, 2020 at 4:19 PM
Edited

This is expected behavior because strict mode processing does not include FTWRL.

Lalit Choudhary April 6, 2020 at 9:08 AM

Hi Sergey,

Thank you for the report.

Sergey Kuzmichev March 31, 2020 at 1:16 PM

After writing this, found https://jira.mariadb.org/browse/MDEV-7808 which is the same issue explained the same way

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Created March 31, 2020 at 1:15 PM
Updated March 6, 2024 at 9:39 PM
Resolved April 7, 2020 at 4:19 PM
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