Richard Payne wrote:
Cache hit % Hit, hit_percent & miss Disk Reads Replaced Insert/Evicts/Invalidates
High Insert and Invalidate = high churn thrugh the FlashCache.
It's implemented as an 8-way Set Associative Cache underneath the WAFL buffer cache. So Evict rate is not really that interesting, but it's of course related to the size of your FlashCache vs the working set size. The latter is very very difficult to determine, it's almost impossible for deadly creatures to find that out
I let those run for a couple of weeks to get a baseline and then enabled lopri_blocks and basically watched what happened. For us (NFS, heavy metadata workloads) I saw the ‘churn’ of the cache go up but we also started getting much higher hit rates.
I agree completely. Higher Disk Read Replaced + higher Hit Rate = better. Better on those with lopri_on? Then run it like that. Workloads may change over time though, so sometimes it can make sense to switch between in intervals between lopri = on and off -- if you can be bothered
And of course: get more FlashCache if you can (it costs, I know)... With more, lopri_blocks will be more effective (of course)
/M