Bug 951588 fix needs revert and re-fixing

[Laurynas Biveinis]

Bug 951588 was about the fact that calling handler ::info from another thread is inherently unsafe because it overwrites the handler state, causing troubles for the handler-owning thread. The fix was to clone handler first, and then run ::info on the cloned handler.

This fix is very fragile: see bug 1113388, bug 1193264, bug 1193308, bug 1206486, bug 1205200, bug 1204859, bug 1206020, and probably others. handler::clone() was not designed for such use.

A better is fix is needed. One option would be to implement new small info-like method for handler that returns the already-available information from the handler without doing a full clone nor info.

[Laurynas Biveinis (laurynas-biveinis)]

It appears that
- Calling info() is safe on a non-cloned handler belonging to this connection. Thus I_S.TEMPORARY_TABLES queries may simply do it.
- Calling neither info() nor clone() is safe on handlers belonging to other connections. Thus for I_S.GLOBAL_TEMPORARY_TABLES the best we can do is to read the existing stats, whatever they happen to be, without calling any method first.

[Roel Van de Paar (roel11)]

Please also check i37704 to see if it is likely the same problem (if so please sent a note from within that issue).

[Roel Van de Paar (roel11)]

Bug 1260151 & bug 1260154 were marked duplicate of this one also.

Laurynas, can we push this forward? We keep running into these sort of issues and it makes run analysis hard.

[Laurynas Biveinis (laurynas-biveinis)]

i37704 analyzed, it is a different problem.

The current issue is close to the top of my TODO.

[Roel Van de Paar (roel11)]

Bug 1367922 - regression?

[Laurynas Biveinis (laurynas-biveinis)]

Not a regression because it is not fixed in the first place yet.

[Laurynas Biveinis (laurynas-biveinis)]

Un-duplicated the individual I_S.GLOBAL_TEMPORARY_TABLES bugs, and will fix the analysed ones without moving away from the use of handler::clone. That should allow GLOBAL_TEMPORARY_TABLES to become subject to QA again, and then the remaining i-s-temp-tables bugs can be fixed as they are analyzed or as the testcases are produced by QA.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-719