Hello,

We have a rather large mongo replica set containing 19,000 dbs. We have an outstanding issue with wiredTiger cache as per https://jira.mongodb.org/browse/SERVER-27700 and https://jira.mongodb.org/browse/SERVER-27753.

As we are expecting the change to be in the next 3.4.x-rc we upgraded our cluster from 3.2.11 to 3.4.2 to understand the current performance characteristics and hope that we would gain some improvement.

Since the upgrade (less than 24 hours) our jobs (which use this cluster) are now taking many hours to finish. In fact some of them have not finished running and we have canceled them.

The following a screen shot of job run times and how mongo 3.2.11 / 3.4.2 impacts the run time.

Please can you provide an upload link and I will provide the diagnostic data for the cluster.

Kind regards,
Luke