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From Chris Anderson <jch...@apache.org>
Subject Re: svn commit: r815404 - /couchdb/branches/0.10.x/etc/couchdb/default.ini.tpl.in
Date Tue, 15 Sep 2009 18:30:37 GMT
On Tue, Sep 15, 2009 at 10:22 AM, Jan Lehnardt <jan@apache.org> wrote:
>
> On 15 Sep 2009, at 19:09, jchris@apache.org wrote:
>
>> Author: jchris
>> Date: Tue Sep 15 17:09:22 2009
>> New Revision: 815404
>>
>> URL: http://svn.apache.org/viewvc?rev=815404&view=rev
>> Log:
>> changed default for 0.10 to delayed_commits = true for fast out of box
>> experience
>
> Chris, please discuss this first on dev@.
>

Sorry about that - just having a strong gut reaction to the potential
of releasing 0.10 that's too slow to use.

Good thing is that this commit got everyone talking on IRC.

The basic tradeoff here is between safety and speed. With a simple
benchmark on my Mac laptop (OSX 10.5) delayed_commits gives ~230
writes/second while we only get about 5/sec with the slow safe option.

I think 5 writes/second is too slow to be useful, so it doesn't matter
how safe it is.

The other perspective is that we shouldn't say we've written something
unless its verifiably on disk. Due to the nature of fsync on various
platforms, this turns out to be non-trivial, as linux allows the disk
write buffer to lie about writes, but OSX does some tricks to force a
flush.

Damien on IRC explained his reasoning:

"so here's my thinking. if it's fast, but broken by default on the
server class OS, then why make it slow on less important consumer
grade machines."

What's left to resolve: if we decide to keep fast as the default in
0.10, we should also make it the default on trunk (until the
server-controlled batches are implemented.)

Chris



-- 
Chris Anderson
http://jchrisa.net
http://couch.io

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