It's perfectly normal/healthy for many small merges below the floor size to
happen.

I think you should first figure out why this node is different from the
others?  Are you sure it's merging CPU cost that's different?

Mike McCandless

http://blog.mikemccandless.com


On Sat, Jul 5, 2014 at 9:51 PM, Kireet Reddy <[email protected]> wrote:

> We have a situation where one of the four nodes in our cluster seems to
> get caught up endlessly merging.  However it seems to be high CPU
> activity and not I/O constrainted. I have enabled the IndexWriter info
> stream logs, and often times it seems to do merges of quite small segments
> (100KB) that are much below the floor size (2MB). I suspect this is due to
> frequent refreshes and/or using lots of threads concurrently to do
> indexing. Is this true?
>
> My supposition is that this is leading to the merge policy doing lots of
> merges of very small segments into another small segment which will again
> require a merge to even reach the floor size. My index has 64 segments and
> 25 are below the floor size. I am wondering if there should be an exception
> for the maxMergesAtOnce parameter for the first level so that many small
> segments could be merged at once in this case.
>
> I am considering changing the other parameters (wider tiers, lower floor
> size, more concurrent merges allowed) but these all seem to have side
> effects I may not necessarily want. Is there a good solution here?
>
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