# Percona for MongoDB inMemory Storage Engine Performance Expectations **URL:** \ **Category:** Percona Server for MongoDB\ **Created:** [January 6, 2018, 7:18am UTC](https://forums.percona.com/t/percona-for-mongodb-inmemory-storage-engine-performance-expectations/6103 "2018-01-06T07:18:32Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![hyurtseven](https://avatars.discourse-cdn.com/v4/letter/h/a4c791/32.png) [@hyurtseven](https://forums.percona.com/u/hyurtseven)\ **Post date:** [January 6, 2018, 7:18am UTC](https://forums.percona.com/t/percona-for-mongodb-inmemory-storage-engine-performance-expectations/6103/1 "2018-01-06T07:18:32Z")
Hi, i have a replica set with 2 inMemory (primary and secondary) and 1 WiredTiger (Hidden) and i was expecting a huge performance impact without indexing all queries with this setup because of the in-memory engine but when i compare my old whole WiredTiger setup with this there is no better performance with in-memory engine, do you think that i’m missing something? ---
**Author:** ![lorraine.pocklington](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/lorraine.pocklington/32/37_2.png) [@lorraine.pocklington](https://forums.percona.com/u/lorraine.pocklington)\ **Post date:** [January 19, 2018, 8:46am UTC](https://forums.percona.com/t/percona-for-mongodb-inmemory-storage-engine-performance-expectations/6103/2 "2018-01-19T08:46:23Z")
If this is a read-only workload then you might not see significant differences if those reads are already in memory. You might see a greater impact on writes. If that’s a wrong assumption, then version and environment information might be needed. Meanwhile, though, this webinar might be of interest as it covers use cases: [url][Upcoming Webinars](https://www.percona.com/resources/webinars/gain-mongodb-advantage-percona-memory-engine%5B/url%5D)