By default Solr uses the “TieredMergePolicy”[1], but it can be configured in solrconfig, see [2]. Merges can be triggered for different reasons, but most commonly by segment flushes (commits) or other merges finishing.
Here is a nice visual demo of segment merging (a bit old but still mostly applies AFAIK): [3] [1] https://lucene.apache.org/core/6_6_0/core/org/apache/lucene/index/TieredMergePolicy.html [2] https://lucene.apache.org/solr/guide/6_6/indexconfig-in-solrconfig.html [3] http://blog.mikemccandless.com/2011/02/visualizing-lucenes-segment-merges.html Tomas > On Sep 7, 2017, at 10:00 AM, calamita.agost...@libero.it wrote: > > > Hi all, > I use SolrCloud with some collections with 3 shards each. > Every day I insert and remove documents from collections. I know that solr > starts optimizer in background to optimize indexes. > Which is the policy that solr applies in order to start optimizer > automatically ? Number of deleted documents? Number of segments? > Thanks.
