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Bug #44723 Larger read_buffer_size values can cause performance

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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.
This commit is contained in:
Anurag Shekhar 2009-08-24 13:15:51 +05:30
parent 0665536995
commit 11dd1d6d84
1 changed files with 7 additions and 4 deletions
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11
mysys/mf_iocache.c
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@ -233,10 +233,13 @@ int init_io_cache(IO_CACHE *info, File file, uint cachesize,
buffer_block = cachesize;
if (type == SEQ_READ_APPEND)
buffer_block *= 2;
if ((info->buffer=
(byte*) my_malloc(buffer_block,
MYF((cache_myflags & ~ MY_WME) |
(cachesize == min_cache ? MY_WME : 0)))) != 0)
/*
Unset MY_WAIT_IF_FULL bit if it is set, to prevent conflict with
MY_ZEROFILL.
*/
myf flag = MYF((cache_myflags & ~ (MY_WME | MY_WAIT_IF_FULL)) |
(cachesize == min_cache ? MY_WME : 0));
if ((info->buffer= (byte*) my_malloc(buffer_block, flag)) != 0)
{
info->write_buffer=info->buffer;
if (type == SEQ_READ_APPEND)