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From Mathias Leppich <mlepp...@muhqu.de>
Subject Re: How many filtered replications is too many?
Date Fri, 06 Jul 2012 09:37:06 GMT
Hi Andreas,

If you say you want to split one large database in many smaller ones as a one-time task, its
probably more efficient to write a script that reads the _changes feed of the large database
and then decides where to put each document. Compared to the 200 filtered replications you
will only need to read the changes feed 1 time instead of 200 times in parallel which will
result in very poor performance because of disk seek times…

Such a migration script is only a few lines of code. And the _changes feed also lets you catchup
after an initial split, you just need to log the passed seq number to know where you left
and start over.

- mathias

On Jul 6, 2012, at 3:37 , Andreas Kemkes wrote:

> I'm trying to split up a monolithic database into smaller ones using filtered continuous
replications in couchdb 1.2.
> 
> I need about 200 of these replications (on a single server) and would like to parallelize
as much as possible.  Yet, when I do, the cpu load gets very high and the system seems to
be crawling, replication seems to be slow, and I'm seeing timeout and other errors.
> 
> How can I best determine what the bottleneck is?
> 
> Are there suggestions on how to configure couchdb to handle it better (I've increased
max_dbs_open to 200)?
> 
> How do I best achieve good throughput?
> 
> This will be a one-time task, so any large measurement / monitoring effort is probably
overkill.
> 
> Any suggestions are much appreciated (including suggestions for different approaches).
> 
> Thanks,
> 
> Andreas


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