we are seeing are seeing a very significant increase in response times after upgrading our elasitc.co cluster from 1.7.6 to 2.4.4.
It generally performs worse across the board. Aggregations seem particularly slow,
- very basic float histogram on nested docs field (single)
it used to have negligible affect on query time on 1.7.6. On 2.4.4 it easily doubles if not triples query time (say 40ms base + 80ms aggregations).
Since 2.4.4 is supposed to have docvalues on by default the assumption is aggregations would fly.
We don't have many docs - cca 8-10mil (incl. nested). Nothing else changed in the cluster. Queries got converted to 2.4.4.
Is there any obvious trick about migrating from 1.7 to 2.4.4 (or 2.* in general) that we've missed?
Note: we haven't reindexed everything from scratch. We captured a snapshot on old 1.7 cluster, restored it to new 1.7 cluster that was later upgraded to 2.4.4. Could this be potentially the cause of degraded performance?