Re: [boost] ACID transactions/flushing/MySQL InnoDB

Subject: Re: [boost] ACID transactions/flushing/MySQL InnoDB
From: Jose (jmalv04_at_[hidden])
Date: 2009-12-10 20:12:49

On Thu, Dec 10, 2009 at 11:02 PM, Stefan Strasser
<strasser_at_[hidden]> wrote:
>> > what I find surprising is the performance of MySQL for small
>> > transactions. while my library spends 90% of its time waiting for the
>> > disk to flush a transaction, InnoDB uses 100% CPU and barely uses any
>> > disk.

> but, including all the SQL parsing, running 10000 small transactions takes
> about 4 seconds on my system.
> while this little code snippet alone takes 6-7 seconds, with much more disk
> usage:
>
>  int fd=open("test.bin",O_RDWR | O_CREAT | O_NOATIME);
>  for(int c=0;c<10000;++c){
>    write(fd,&data,1);
>    fsync(fd);
>  }
>
> neither fdatasync(), O_WRONLY, nor writing whole sectors instead of just a
> byte make a difference. MySQL also claims to use fsync on the page you
> linked.
>
> do you have an explanation for this?

You should be comparing using msync (not fsync). Also, the high cpu
usage might be caused by innodb gzip compression

regards