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POExtraordinarily poor performance from MongoDB in write intensive application
 

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    <p>I'm running write intensive MongoDB for a web app and I'm getting extraordinarily poor performance from it. This being said, I'm fairly certain that the problem has more to do with up our code, setup and/or our usage than in mongo itself.</p> <p>I'm about to crack my head open with a sledgehammer out of despair so I was wondering if anybody would mind looking at some of the outputs I've prepared to see if anything seems problematic.</p> <ul> <li><a href="http://www.fuitad.com/mongo/db.stats.txt" rel="nofollow">db.stats()</a></li> <li><a href="http://www.fuitad.com/mongo/fstab-mdadm-iostat.txt" rel="nofollow">fstab, mdadm and iostat -xm 2</a></li> <li><a href="http://www.fuitad.com/mongo/mongostat.txt" rel="nofollow">mongostat</a></li> </ul> <p>The code is not too complicated (it's in PHP, btw). It's pretty much a lot of ->find() and ->update(). I made sure to use indexes for both calls and confirmed they were indeed being used by doing explain() on the queries.</p> <p>I've tried 1 server (ec2 m2.2xlarge), 4 servers (2 shards of 2 reps) and 9 servers (3 shards of 3 reps) and wasn't able to get much out of those.</p> <p>On good moments, I can't get anything more than 1500 writes per second (insert + update). Most of the time, I'm lucky to reach a combined amount of 100 insert/update and I always have a big "locked %" and a lot of queries queued "qr|qw".</p> <p>Right now, I have a script that's running and it's crawling. The worst thing is, when I look at mongostat for a while, the amount of RAM used in "res" is about 50% of the server's available RAM and there's more than enough RAM to fit the indexes of all collections. There's no reason why this isn't spitting out data like crazy. </p> <p>I must have recoded the app 2-3 times already, trying to find better access patterns for the data. I've read everything I could read on indexes, updating, shard keys and what not. All the servers I put mongo on are using a 8 EBS disks raid 10 setup with some performance tweaks added (blockdev, noatime, etc…).</p> <p>I know the problem is on my end and I'm not blaming mongodb. I know bigger companies than me are using it for write intensive applications and that they absolutely love it (foursquare for example). At the same time, I just can't understand what I'm doing wrong and why I'm getting such poor performance, no matter what I do.</p> <p>Additional Info:</p> <ul> <li>All servers (client and server) are running Ubuntu 10.04 LTS with MongoDB 1.8.2</li> <li>All servers are on EC2 East and in the same zone</li> <li>Currently, I'm back at 1 m2.2xlarge server (4 cores, 34.2 GB RAM) until I can figure out where the problem is.</li> </ul>
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