I'm trying to benchmark search performance (Elasticsearch 6.0.1) on different FS mode.
Index size is around 5GB each (10 indexes in total).
Search is done by doing the following:
Open Index1 --> Search on Index1 --> Open Index2 --> Search on Index2 --> ... --> Open Index10 --> Search on Index10
The process above is repeated 5 times to get average across all search time.
On mmapfs it seems like first iteration is much more expensive and incurs a lot of Disk IO operations. Is this because mmapfs needs to build some sort of mapping on RAM?
On niofs, it seems stable for every iteration, and incurs less disk IO.
But I observe that search time on mmapfs is slightly faster than niofs.
and when system is performing heavy indexing, both mmapfs and niofs performs poorly on search.
Any rule of thumb on how to decide whether to choose mmapfs or niofs?