MDL resource held outside TO isolation

[Teemu Ollakka]

Regression test for lp:861212 causes inconsistency. The following log snippet reveals that some MDL resources are held outside TOI critical section by locally executed ALTER.

121030 16:36:34 [Note] [Debug] WSREP: galera/src/replicator_smm.cpp:to_isolation_begin():965: Executing TO isolated action: source: 2f58f6ca-229f-11e2-0800-9c24304618ba version: 2 local: 1 state: APPLYING flags: 65 conn_id: 22 trx_id: -1 seqnos (l: 414, g: 7751450, s: 7751437, d: 7751449, ts: 1351607794729079543)
121030 16:36:34 [Note] WSREP: TO BEGIN: 7751450, 2
121030 16:36:34 [Note] WSREP: TO END: 7751450, 2 : ALTER TABLE comm02 DROP COLUMN d
121030 16:36:34 [Note] [Debug] WSREP: galera/src/replicator_smm.cpp:to_isolation_end():991: Done executing TO isolated action: source: 2f58f6ca-229f-11e2-0800-9c24304618ba version: 2 local: 1 state: APPLYING flags: 65 conn_id: 22 trx_id: -1 seqnos (l: 414, g: 7751450, s: 7751437, d: 7751449, ts: 1351607794729079543)
121030 16:36:34 [Note] [Debug] WSREP: galera/src/replicator_smm.cpp:to_isolation_begin():965: Executing TO isolated action: source: 2f58f6ca-229f-11e2-0800-9c24304618ba version: 2 local: 1 state: APPLYING flags: 65 conn_id: 21 trx_id: -1 seqnos (l: 415, g: 7751451, s: 7751438, d: 7751450, ts: 1351607794745565333)
121030 16:36:34 [Note] WSREP: TO BEGIN: 7751451, 2
121030 16:36:34 [Note] WSREP: MDL conflict
request: (21 seqno 7751451 wsrep (2, 1, 0) cmd 3 3 ALTER TABLE comm02 ADD COLUMN (d DATETIME))
granted: (22 seqno 7751450 wsrep (2, 1, 0) cmd 3 3 ALTER TABLE comm02 DROP COLUMN d)
121030 16:36:34 [Note] WSREP: MDL BF-BF conflict
request: (21 seqno 7751451 wsrep (2, 1, 0) cmd 3 3 ALTER TABLE comm02 ADD COLUMN (d DATETIME))
granted: (22 seqno 7751450 wsrep (2, 1, 0) cmd 3 3 ALTER TABLE comm02 DROP COLUMN d)
121030 16:36:34 [Note] WSREP: TO END: 7751450
121030 16:36:34 [Note] WSREP: TO END: 7751451, 2 : ALTER TABLE comm02 ADD COLUMN (d DATETIME)
121030 16:36:34 [Note] [Debug] WSREP: galera/src/replicator_smm.cpp:to_isolation_end():991: Done executing TO isolated action: source: 2f58f6ca-229f-11e2-0800-9c24304618ba version: 2 local: 1 state: APPLYING flags: 65 conn_id: 21 trx_id: -1 seqnos (l: 415, g: 7751451, s: 7751438, d: 7751450, ts: 1351607794745565333)

[Seppo Jaakola (seppo-jaakola)]

regression test lp1073220 can surface reliably inconsistencies in schema level

[Seppo Jaakola (seppo-jaakola)]

Problem seems to be that DDL statement can hold MDL, either before TO isolation processing started or after it has ended. This can cause DDL vs DDL conflict over some MDL resource.

Commit in revision: http://bazaar.launchpad.net/~codership/codership-mysql/wsrep-5.5/revision/3814 fixes these race vulnerabilities.