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From Jean-Yves Moulin <jean-yves.mou...@eileo.com>
Subject Issues with terabytes databases
Date Tue, 22 Apr 2014 14:09:59 GMT
Hi everybody,

we use CouchDB in production for more than two years now. And we are almost happy with it
:-) We have a heavy writing workload, with very few update, and we never delete data. Some
of our databases are terabytes with billions of documents (sometimes 20 millions of doc per
day). But we are experiencing some issues, and the only solution was to split our data: today
we create a new database each week, with even and odd on two different servers (thus we have
on-line and off-line servers). This is not perfect, and we look forward BigCouch :-)

Below is some of our current problems with these big databases. For the record, we use couchdb-1.2
and couchdb-1.4 on twelve servers running FreeBSD (because we like ZFS).

I don't know if these issues are known or not (or specific to us).

* Overall speed: we are far from our real server performance: it seems that CouchDB is not
able to use the full potential of the system. Even with 24 disks in RAID10, we can't go faster
that 2000 doc/sec (with an average document size of 1k, that's only a few MB/s on disk) on
replication or compaction. CPU and disk are almost idle. Tweaking the number of Erlang I/O
thread doesn't help.

* Insert time: At 1000 PUT/sec the insert time is good, even without bulk. But it collapses
when launching view calculation, replication or compaction. So, we use stale view in our applications
and views are processed regularly by a crontab scripts. We avoid compaction on live servers.
Compaction are launched manually on off-line servers only. We also avoid replication on heavy
loaded servers.

* Compaction: When size of database increase, compaction time can be really really long. It
will be great if compaction process can run faster on already compressed doc. This is our
biggest drawback, which implies the database split each week. And the speed decreases slowly:
compaction starts fast (>2000 doc/sec) but slow down to ~100 doc/sec after hundred of millions
of documents.

Is there other people using CouchDB this kind of database ? How do you handle a write-heavy
workload ?

Sorry for my english and thank you for the reading.

Best,


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