Suboptimal buffer pool locking for I_S.INNODB_BUFFER_POOL_PAGES*

[Laurynas Biveinis]

5.1 code (5.5 is mostly the same with multiple buf pool instance support):

buf_pool_mutex_enter();

for (all buf_pool->chunks)
   for (all pages in a chunk)
      fill row

buf_pool_mutex_exit();

Issues:
1) Blocks the buffer pool for the whole query duration.
2) After the XtraDB mutex split the blocking does not seem to actually protect the fields it accesses (if one does not count the "protection" provided by the blocked server...).

Suggested fix:
The buf_pool->chunks is allocated at startup and is constant. Thus, we only have to lock individual buffer pages for each I_S result row, or even accept dirty info without any locking. The only other precaution then we need to take is to handle server shutdowns in the middle of I_S query correctly.

[Laurynas Biveinis (laurynas-biveinis)]

Setting as "Confirmed" due to 1) above. 2) still needs verifying.

[Alexey Kopytov (akopytov)]

The same applies to I_S.INNODB_BUFFER_POOL_PAGES_BLOB.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-1938