[ZODB-Dev] Use of fsync in FileStorage

[Tim Peters]

[Paul Roe]
> Some more stats 10000 transactions per run both boxes are single Opteron
> 246
>
> Debian Unstable Zope2.7 Filestorage.py Rev 1.135.6.5
> 4x36G WD360GD SATA 10K RAID 10 Array (Intel SRCS14L)
>
> 0 fsync 2.90725 seconds, 3439.68  txn/sec

Congratulations!  That's the only box so far to beat my Gateway Windows
laptop on this measure <wink>.

> 1 fsync 9.46928 seconds, 1056.05  txn/sec 
> 2 fsync 10.4368 seconds,  958.152 txn/sec
>
> Debian Pure64  Zope2.7  Filestorage.py Rev 1.135.6.5
> 2x70G WD740GD SATA 10K RAID 1 Array (Intel SRCS14L)
>
> 0 fsync 2.92782 seconds, 3415.52 txn/sec
> 1 fsync 8.1819  seconds, 1222.21 txn/sec
> 2 fsync 9.50206 seconds, 1052.4  txn/sec

So 1 fsync slows by a factor ~3.5, and 2 is minor marginal loss beyond that.
Given what you know so far, would you rather run in production with 0, 1, or
2 of these puppies?  You're not going to throw 1000 txn/sec at ZODB, so even
your slowest rates here are "more than enough".  OTOH, do you believe the
fsyncs buy you something worth having?

At this point it seems the choice has at least as much to do with perception
as with technical merit, so I'm also keen to know what perceptions are.