Release table metadata lock for SELECT when ready to fetch the rows

[Valerii Kravchuk]

See this upstream bug report for the details:

http://bugs.mysql.com/bug.php?id=76588

This is essentially a feature request to implement a relaxed metadata locking model for SELECTs (the same as we have for PREPARE maybe?).

Is this possible any time soon?

[Valerii Kravchuk (valerii-kravchuk)]

It seems lock released after we execute PREPARE is then taken again after we executed EXECUTE. So, real question remain:

Is there any way to release metadata lock:

mysql> select * from performance_schema.metadata_locks\G
*************************** 1. row ***************************
          OBJECT_TYPE: TABLE
        OBJECT_SCHEMA: test
          OBJECT_NAME: t
OBJECT_INSTANCE_BEGIN: 140044187351136
            LOCK_TYPE: SHARED_READ
        LOCK_DURATION: TRANSACTION
          LOCK_STATUS: GRANTED
               SOURCE: sql_parse.cc:5585
      OWNER_THREAD_ID: 24
       OWNER_EVENT_ID: 16

(the above is the output from 5.7) as soon as we've determined list of columns (prepared the statement) and then do not set it again, even when autocommit=0?

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-2462