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Re: [PATCH] Disable fsync at transaction commit

From: Branko Čibej <brane_at_xbc.nu>
Date: 2003-02-24 04:23:15 CET

Benjamin Pflugmann wrote:

>>How unfortunate. 10% is nothing to sneer at, but it seems that Windows
>>is a terrible host for any kind of database. My box is a dual Athlom MP
>>2200+ (1.8GHz) with 1GB of memory and 4-way RAID 5 disks, running
>>Windows XP. Hm, maybe the fsyncs are that much slower because of the
>>RAID thing.
>>
>>
>
>Very well possible. Dependend on implementation, RAID5 is slower than a
>plain disk at writes, but never better.
>
Uh, no, it will be better on reads, because it can parallelize them
(just like RAID0) -- but that doesn't help the fsync, of course.

>But let me guess, the RAID uses SCSI disks?
>
Nope, it's a H/W IDE raid controller (the 3ware Escalade, if you're
interested about such things).

> Most (all?) IDE disks lie
>about writing. They are using write-caching, while SCSI disks only say
>they have written stuff to disk, when it really is on the platter.
>
>If I disable write-caching with my IDE disk (hdparm -W0 /dev/hdb, note
>that some drives ignore that request and continue to use the write
>cache), make check needs
>
> - 48 mins (without the patch)
> - 34 mins (with patch)
>
>which is more in the range of your results.
>
Nope, mine was 56 to 34 minutes. :-)

[snip]

>Maybe there should also be some way for people to play it more fast
>than safe (e.g. allow to disable synchronous syncs at all), if that
>meets their priorities.
>
>
That's the point of the "svnadmin create --bdb-txn-nosync" patch, which
I'll commit one of these days. I can imagine disabling the fsyncs for
cvs2svn and large dump/load cycles. You'd probably turn them back on for
production, of course.

-- 
Brane Čibej   <brane_at_xbc.nu>   http://www.xbc.nu/brane/
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Received on Mon Feb 24 04:23:58 2003

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