Is the fsync() fake on FreeBSD6.1?

leo huang leo.huang.list at
Tue Jun 27 02:18:53 UTC 2006


I benchmarked MySQL 4.1.18 on FreeBSD 6.1 and Debian 3.1 using Super Smack
1.3 some days ago.

The benchmark table  is
CREATE TABLE `Account` (
  `aid` int(11) NOT NULL auto_increment,
  `name` char(20) NOT NULL default '',
  `flag` int(11) NOT NULL default '0',
  `uidcount` int(11) NOT NULL default '0',
  `balance` int(11) NOT NULL default '0',
  `point` int(11) NOT NULL default '0',
  `blocktm` int(11) NOT NULL default '0',
  `ipnum` int(10) unsigned default NULL,
  `newdate` datetime default NULL,
  PRIMARY KEY  (`aid`),
  UNIQUE KEY `name` (`name`)

And it has 10,000,000 rows.

The SQL statement is
update Account set balance= balance + 1 where aid=?;

The result is followed:
OS                Clients        Result(queries per second)         TPS(got
from iostat)
FreeBSD6.1    50               516.1
about 2000
Debian3.1       50               49.8
about 200

The result surprise me. The MySQL Performance on FreeBSD6.1 is about 10
times of on Debian3.1,and the output of iostat also shows it.

I know that MySQL uses fsync() to flush both the data and log files at
default when using innodb engine( Our
evaluating computer only has a 10000RPM SCSI hard disk. I think it can do
about 200 sequential fsync() calls per second if the fsync() is real.

Is the fsync() on FreeBSD6.1 fake? I mean than the data is only written to
the drives memory and so can be lost if power goes down. And how I can
confirm this?

If the fsync() is fake, how can I get the real fsync?

Any comment is welcome!

1. Our evaluating computer is DELL PowerEdge 1650。Its hardware configuration
is followed:
    CPU: 2 * Intel Pentium III 1.33GHz 512KB Level 2 Cache(smp)
    Memory: 1024MB ECC SDRAM
    HD: SEAGATE ST336706LC(36GB Ultra160 SCSI 10000RPM)
    NIC    : Intel(R) PRO/1000 Network Connection

2. Some important parameters in MySQL configuration file are here:
    innodb_buffer_pool_size = 384M
    innodb_additional_mem_pool_size = 20M
    innodb_log_file_size = 100M
    innodb_log_buffer_size = 8M
    innodb_flush_log_at_trx_commit = 1
    innodb_lock_wait_timeout = 50

Leo Huang

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