Hi Anurag,
On Fri, Aug 21, 2009 at 09:55:46AM +0000, Anurag Shekhar wrote:
> #At file:///home/anurag/mysqlsrc/mysql-5.0-bugteam-44723/ based on
> revid:joro@stripped
>
> 2792 Anurag Shekhar 2009-08-21
> Bug #44723 Larger read_buffer_size values can cause performance
> decrease for INSERTs
>
>
> Bulk inserts (multiple row, CREATE ... SELECT, INSERT ... SELECT) into
> MyISAM tables were performed inefficiently. This was mainly affecting
> use cases where read_buffer_size was considerably large (>256K) and low
> number of rows was inserted (e.g. 30-100).
>
> The problem was that during I/O cache initialization (this happens
> before each bulk insert) allocated I/O buffer was unnecessarily
> initialized to '\0'.
>
> This was happening because of mess in flag values. MyISAM informs I/O
> cache to wait for free space (if out of disk space) by passing
> MY_WAIT_IF_FULL flag. Since MY_WAIT_IF_FULL and MY_ZEROFILL have the
> same values, memory allocator was initializing memory to '\0'.
>
> The performance gain provided with this patch may only be visible with
> non-debug binaries, since safemalloc always initializes allocated memory
> to 0xA5A5...
> @ 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 2009-08-21 09:55:41 +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)
Ok, you removed tabs, but forgot to add spaces instead.
Regards,
Sergey
--
Sergey Vojtovich <svoj@stripped>
MySQL AB, Software Engineer
Izhevsk, Russia, www.mysql.com
