CODEWITHSUNDEEP
solrlucenefull-text-searchelasticsearch
Akash Bhunchal
Akash Bhunchal

Reputation: 79

Confused about the affect of mergefactor on searching and indexing

Solr/Lucene documentation says the following:

1) High mergefactor leads to better indexing performance as writing the index to disk is minimized and the merging of segments too happens less frequently, but leads to lower querying speed as the number of segments are high and searching them takes time.

2) Low merge factor leads to poor indexing performance but faster query for the same reasons as above.

I have also learnt that the merging happens in parallel in the background and is not part of the indexing request.

Questions:

1) When I have a low mergefactor what is causing low indexing performance ? Having to write the index to the disk more often or the merging ? Writing to disk is understandable bottleneck. But if frequent merging too is a reason which is happening in the background then it should slow down the querying too as the querying thread too would be in contention of the CPU along with the merging threads.

2) Is the querying blocked when the segment merge happens ?

Upvotes: 0

Views: 314

Answers (1)

naresh
naresh

Reputation: 2113

1)Frequent merging (low merge-factor) causes low indexing performance. But a low-merge factor is likely to improve search performance because there are less segments to search in

2)No

Upvotes: 1

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