From: Dmitry Lenev
Date: October 24 2011 7:42am
Subject: bzr push into mysql-5.5 branch (Dmitry.Lenev:3588 to 3589) Bug#13116518
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X-Bug: 13116518
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 3589 Dmitry Lenev	2011-10-23
      Fix for bug #13116518 - "OPEN_TABLES() SHOULD NOT ALLOCATE AND FREE 
      NEW_FRM_MEM WITHOUT NEEDING TO".
      
      During the process of opening tables for a statement, we allocated
      memory which was used only during view loading even in cases when the
      statement didn't use any views. Such an unnecessary allocation (and
      corresponding freeing) might have caused significant performance
      overhead in some workloads. For example, it caused up to 15% slowdown
      in a simple stored routine calculating Fibonacci's numbers.
      
      This memory was pre-allocated as part of "new_frm_mem" MEM_ROOT
      initialization at the beginning of open_tables(). 
      
      This patch addresses this issue by turning off memory pre-allocation
      during initialization for this MEM_ROOT. Now, memory on this root
      will be allocated only at the point when the first .FRM for a view is 
      opened.
      
      The patch doesn't contain a test case since it is hard to test the
      performance improvements or the absence of memory allocation in our
      test framework.

    modified:
      sql/sql_base.cc
 3588 Ashish Agarwal	2011-10-22 [merge]
      bug#11758979 - 51252: ARCHIVE TABLES STILL FAIL UNDER STRESS
                            TESTS: CRASH, CORRUPTION, 4G MEMOR
      
      Issue: Valgrind errors due to checksum and optimize
             query against archive tables with null columns.
             Table record buffer was not initialized.
      
      Solution: Initialize the record buffer.

    modified:
      mysql-test/r/archive.result
      mysql-test/t/archive.test
      storage/archive/ha_archive.cc
=== modified file 'sql/sql_base.cc'
--- a/sql/sql_base.cc	2011-08-24 12:22:11 +0000
+++ b/sql/sql_base.cc	2011-10-23 05:37:35 +0000
@@ -4810,10 +4810,11 @@ bool open_tables(THD *thd, TABLE_LIST **
   }
 
   /*
-    temporary mem_root for new .frm parsing.
-    TODO: variables for size
+    Initialize temporary MEM_ROOT for new .FRM parsing. Do not allocate
+    anything yet, to avoid penalty for statements which don't use views
+    and thus new .FRM format.
   */
-  init_sql_alloc(&new_frm_mem, 8024, 8024);
+  init_sql_alloc(&new_frm_mem, 8024, 0);
 
   thd->current_tablenr= 0;
 restart:

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