In our previous attempt to upgrade our production cluster to 3.0, we had to roll back from the WiredTiger engine on primary servers.

Since then, we switched back our whole cluster to 3.0 MMAPv1 which has brought us some better performances than 2.6 with no instability.

Production checklist

We decided to use this increase in performance to allow us some time to fulfil the entire production checklist from MongoDB, especially the migration to XFS. We’re slowly upgrading our servers kernels and resynchronising our data set after migrating from ext4 to XFS.

Ironically, the strong recommendation of XFS in the production checklist appeared 3 days after our failed attempt at WiredTiger… This is frustrating but gives some kind of hope.

I’ll keep on posting on our next steps and results.

Our hero WiredTiger Replica Set

While we were battling with our production cluster, we got a spontaneous major increase in the daily volumes from another platform which was running on a single Replica Set. This application is write intensive and very disk I/O bound. We were killing the disk I/O with almost a continuous 100% usage on the disk write queue.

Despite our frustration with WiredTiger so far, we decided to give it a chance considering that this time we were talking about a single Replica Set. We were very happy to see WiredTiger keep up to its promises with an almost shocking serenity.

Disk I/O went down dramatically, almost as if nothing was happening any more. Compression did magic on our disk usage and our application went Roarrr !