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From Mark Miller <>
Subject Re: Solr soft commits
Date Fri, 11 May 2018 04:44:39 GMT
A soft commit does not control merging. The IndexWriter controls merging
and hard commits go through the IndexWriter. A soft commit tells Solr to
try and open a new SolrIndexSearcher with the latest view of the index. It
does this with a mix of using the on disk index and talking to the
IndexWriter to see updates that have not been committed.

Opening a new SolrIndexSearcher using the IndexWriter this way does have a
cost. You may flush segments, you may apply deletes, you may have to
rebuild partial or full in memory data structures. It's generally much
faster than a hard commit to get a refreshed view of the index though.

Given how SolrCloud was designed, it's usually best to set an auto hard
commit to something that works for you, given how large it will make tlogs
(affecting recovery times), and how much RAM is used. Then use soft commits
for visibility. It's best to use them as infrequently as your use case

- Mark

On Thu, May 10, 2018 at 10:49 AM Shivam Omar <>

> Hi,
> I need some help in understanding solr soft commits.  As soft commits are
> about visibility and are fast in nature. They are advised for nrt use
> cases. I want to understand does soft commit also honor merge policies and
> do segment merging for docs in memory. For example, in case, I keep hard
> commit interval very high and allow few million documents to be in memory
> by using soft commit with no hard commit, can it affect solr query time
> performance.
> Shivam
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- Mark

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