bzr commit into mysql-5.0-bugteam branch (anurag.shekhar:2788) Bug#44723

[Anurag Shekhar]

#At file:///home/anurag/mysqlsrc/mysql-5.0-bugteam-44723/ based on revid:li-bing.song@stripped

 2788 Anurag Shekhar	2009-08-14
      Bug #44723 Larger read_buffer_size values can cause performance 
                 decrease for INSERTs
      
      Large number of calls to 'memset' to initialize the bugger to mulls 
      where causing the performance drop.
      my_malloc routine initializes the buffer if MY_ZEROFILL flag is set. 
      In this use case MY_ZEROFILL is set unintentionally due to presence
      MY_WAIT_IF_FULL which is not meant for my_malloc but has same value 
      as MY_ZEROFILL. Unsetting this flag before calling my_malloc solves
      the problem.
      
      The performance improvement from this patch will be visible only on 
      release build as the debug build uses a safemalloc routine which 
      initializes the buffer with ALLOC_VAL (0xA5) if MY_ZEROFILL is not set.
     @ mysys/mf_iocache.c
        Remove MY_WAIT_IF_FULL from myflags before calling my_malloc
        to prevent conflict with MY_ZEROFILL.

    modified:
      mysys/mf_iocache.c
=== modified file 'mysys/mf_iocache.c'
--- a/mysys/mf_iocache.c	2007-03-28 17:46:42 +0000
+++ b/mysys/mf_iocache.c	2009-08-13 19:08:56 +0000
@@ -235,8 +235,8 @@ int init_io_cache(IO_CACHE *info, File f
 	buffer_block *= 2;
       if ((info->buffer=
 	   (byte*) my_malloc(buffer_block,
-			     MYF((cache_myflags & ~ MY_WME) |
-				 (cachesize == min_cache ? MY_WME : 0)))) != 0)
+			   MYF(((cache_myflags & ~ (MY_WME | MY_WAIT_IF_FULL)) |
+				 (cachesize == min_cache ? MY_WME : 0))))) != 0)
       {
 	info->write_buffer=info->buffer;
 	if (type == SEQ_READ_APPEND)


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