[Mailman-Developers] Problem with MM after power outage

[Harald Meland]

[Barry Warsaw]

> Except that when I did some very simple tests, I saw a 97% hit in
> performance with fsync turned on.

Ouch.  That's pretty severe, all right.

Even though I would *guess* that most "casual" Mailman sites would
pull through an effective halving of performance without any problems,
that is merely a guess... thus, I'm not at all sure that set of sites
that would be in trouble with such a big performance hit is disjoint
from the set of sites that don't read upgrade documentation very
carefully.

> This on a RH9, ext3 Linux box of the Dell Optiplex variety.  That
> makes me very nervous to add in a patch release that won't have any
> beta testing.

I hadn't considered the "no beta testing" part of this.

Reconsidering now, I agree that such a big performance hit in a
"bugfix" release ought to be the cause of quite a bit of nervousness
on behalf of the release issuer... :-)

> I'm happy to re-address this for the next major release, but for
> 2.1.3 I don't want to enable fsync by default, and I definitely
> don't want to do any probing/guessing of filesystems, etc.

That sounds like a good plan to me.



However, I'm not sure I understand why this shouldn't be configurable
in mm_cfg; is that just to keep the number of configurable variables
down?


FWIW, PostgreSQL exposes an "do fsync(2)" option in it's global config
file; on my Debian system, the option is preceded with this comment:

  # A special note on FSYNC:
  # FSYNC only affects writes to the WAL (Write-Ahead Log).  Turning it
  # off will give some increase in performance, but at the risk of data-
  # corruption in the event of power failure or other disaster.  It is on
  # by default.  I strongly recommend you not to turn it off.

-- 
Harald