maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxxx>]

Hi, Vladislav!

On Apr 04, Vladislav Vaintroub wrote:
> 
> Hi Serg,
> 
> > Hi, Vladislav!
> > 
> > > +        srv_use_atomic_writes = (ibool) innobase_use_atomic_writes;
> > 
> > Is that the typical usage pattern in the innodb code?
> > Because it looks a bit silly to me, why couldn't you create a sysvar
> > directly on srv_use_atomic_writes, why an intermediate
> > innobase_use_atomic_writes variable?
> 
> Yes, this is typical usage pattern in Innodb. Bit weird, I agree.  Every
> innobase_xxx variable has an srv_xxx counterpart.  I have no clue why it is
> so, but I did not want to disturb their existing conventions:)

Ok, good that you and Laurinas have figured that out :)

Not that I understand why bool == ulint, but I'm not suggesting to break
this convention.

> > it'd be nice if you could try os_file_set_atomic_writes() here to
> > see if that works. This function creates and opens quite a few
> > files, you could use one of them to mark it for atomic writes, and
> > if that would fail, you'd disable atomic writes, and wouldn't change
> > innobase_file_flush_method and innobase_use_doublewrite.
> 
> It is tricky to do it before files are opened the first time , without
> moving lot of code around - there is non-trivial parsing of tablespace names
> later on in open_or_create_data_files(), just to figure out directories and
> filenames.

I mean, you can try your function on any other file, not necessarily
on the tablespace. Even on a temporary file, like with

  int fd = mysql_tmpfile("ib");
  if (os_file_set_atomic_writes(fd)) ...
  my_close(fd);

> > Btw, why not to use posix_fallocate whenever it's available?
> > Or, at least, with its own --innodb-use-fallocate option?
> 
> Yes, I guess it (the new option) is a good idea.  I created a followup patch
> that introduces the option
> http://lists.askmonty.org/pipermail/commits/2013-April/004569.html . I set
> default to ON.  What do you think?

There are two related threads:

https://lists.launchpad.net/maria-developers/msg05068.html
and the one in internals@ mysql list, starting from
http://lists.mysql.com/internals/38679

In particular, I noticed this part
"
  I relied on that fallocate does not need fsync since metadata is
  protected by filesystem journal. But I am not confident whether it is
  true. I'm wondering if this patch may lead InnoDB committing schema to
  not function normally. 
"

What do you know about it, does one need to sync after posix_fallocate()?
What if the filesystem is not journalling?

Regards,
Sergei