[PoC] rounding ms by default

[ppisljar]

PoC: round now to 0ms in dateMath
Goal: increase ES cache hits

[ppisljar]

i compared average request time when using the rounding compared to not using the rounding:
(lens, single layer, 3 metrics, terms agg, from now-1y to now

• average request time without rounding 41s
• average request time with rounding 41s

there is no visible difference between average request times when using the rounding or not.

However, we hypothesise that using the rounding might increase the number of time es cache is hit (which makes requesrts way faster, in my tests average response when hitting the cache (running the test second time) was 1.5s

[ppisljar]

After more in depth look i think rounding will not (significantly) increase the number of hits in the cache, here is why:

To hit the cache multiple queries would need to be made with same time filter. When using multiple same queries on single dashboard this is already guaranteed thru nowProvider which gives same 'now' to all panels. So this could only play a role in multiuser scenarios.

However user2 would need to run the same query as user1 at mostly the same time (only ms difference allowed). In this case when cache is not yet hit by the first user the second user will anyway need to wait for the query to complete, so this will not get him any performance benefits in terms of time to response. It may however improve elasticsearch memory/cpu utilization ?

[ppisljar]

We could make the rounding period configurable. If rounding would be set to 1 minute then this would work:

• user 1 sends a query at 01 seconds, lets say it takes 30 seconds to load, user 2 tries to send same query at 31 second and gets results from cache. On high load kibana instandces even when rounding to 1s we might still see improvement.

open question: is this seen as a user or sys admin setting ? (should it be in datepicker or in advanced settings ? )