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From Stephen Bartell <snbart...@gmail.com>
Subject tinkering with limits while replicating
Date Tue, 05 Feb 2013 01:15:44 GMT
Hi all,

I'm hitting some limits while replicating , I'm hoping someone could advise.  
Im running this in a VM on my macbook with the following allocated resources:
ubuntu 11.04
4 cores @ 2.3ghz
8 gb mem

I'm doing a one-to-many replication.  
1) I create one db named test. 
2) Then create [test_0 .. test_99] databases.  
3) I then set up replications from test -> [test_0 .. test_99].  100 replications total.
4) I finally go to test and create a doc, hit save.

When I hit save, futon becomes completely unresponsive for around 10sec.  It eventually returns
to normal behavior.

Tailing the couchdb log I find waves of the following errors:
[Tue, 05 Feb 2013 00:46:26 GMT] [info] [<0.6936.1>] Retrying POST request to http://admin:*****@localhost:5984/test_25/_revs_diff
in 1.0 seconds due to error {code,503}

I see that the replicator is finding the server to be unresponsive.  The waves of these messages
show that replicator retries in 0.25 sec, then 0.5 sec, then 1sec, then 2sec.  This is expected.
 Everything settles done after about 4 retries.  

So my first thought is resource limits.  I threw the book at it and set :
1) max_dbs_open: 500
2) os_process_limit: 5000
3) http_connections: 20000
4) ulimit -Sn 4096 (the hard limit is 4096)

I really don't know whats reasonable for these values relative to how many replications I
am setting up.  So these values, save max_dbs_open,  are all stabs in the dark.

No change in performance.

So, I'm at a loss now.  what can I do to get all this to work? Or what am I doing wrong? 
And note that this is only a test.  I aim to quadruple  the amount of replications and have
lots and lots of insertions on the so called "test" database.  Actually, there will be several
of these one-to-many databases.

I've heard people get systems up to thousands of dbs and replicators running just fine.  So
I hope Im just not offering to right sacrifices up to couchdb yet.

Thanks for any insight,

sb


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