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Subject: Re: delayed_commits false
From: Damien Katz <damien@apache.org>
In-Reply-To: <4C31FF1A.30002@gmail.com>
Date: Tue, 6 Jul 2010 15:06:27 -0700
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To: dev@couchdb.apache.org


On Jul 5, 2010, at 8:49 AM, Volker Mische wrote:

> Hi All,
>=20
> delayed_commits were enabled to have better performance especially for =
single writers. The price you pay for is that you potentially lose up to =
one second of writes in case of a crash.
>=20
> Such a setting makes sense, though in my opinion it shouldn't be =
enabled by default. I expect* that people running into performance =
issues at least take a look at the README or a FAQ section somewhere. =
There the delayed_commit setting could be pointed out.
>=20
> I'd like to be able to say that on a vanilla CouchDB it's hard to lose =
data, but I can't atm. I'm also well aware that there will be plenty of =
performance tests when 1.0 is released and people will complain (if =
delayed_commits would be set to false by default) that it is horrible =
slow. Though safety of the data is more important for me.
>=20
> If the only reason why delayed_commits is true by default are the =
performance tests of some noobs, I really don't think it's a price worth =
paying.
>=20
> *I know that in reality people don't
>=20
> I would like to see delayed_commits=3Dfalse for 1.0

Last year we turned off delayed commits by default. We got lots of =
complaints, the performance impact was too great. So we switched it =
back. We aren't the first storage engine to go around on this. For =
example, Apple's core data switched to using full fsyncs for each write =
in 10.4, but then switched it back for 10.5:

=
http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/Core=
Data/Articles/cdPersistentStores.html

"Important: The default behaviors in Mac OS X v10.4 an 10.5 are =
different. In Mac OS X v10.4, SQLite uses FULL_FSYNC by default; in Mac =
OS X v10.5 it does not."

Anyway, we can improve the documentation warning's, etc, but we should =
stay with the current defaults.

-Damien

>=20
> Cheers,
>  Volker