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From Zheng Lin Edwin Yeo <>
Subject Re: Merging of index in Solr
Date Tue, 21 Nov 2017 16:10:48 GMT
I am using the IndexMergeTool from Solr, from the command below:

java -classpath lucene-core-6.5.1.jar;lucene-misc-6.5.1.jar

The heap size is 32GB. There are more than 20 million documents in the two


On 21 November 2017 at 21:54, Shawn Heisey <> wrote:

> On 11/20/2017 9:35 AM, Zheng Lin Edwin Yeo wrote:
>> Does anyone knows how long usually the merging in Solr will take?
>> I am currently merging about 3.5TB of data, and it has been running for
>> more than 28 hours and it is not completed yet. The merging is running on
>> SSD disk.
> The following will apply if you mean Solr's "optimize" feature when you
> say "merging".
> In my experience, merging proceeds at about 20 to 30 megabytes per second
> -- even if the disks are capable of far faster data transfer.  Merging is
> not just copying the data. Lucene is completely rebuilding very large data
> structures, and *not* including data from deleted documents as it does so.
> It takes a lot of CPU power and time.
> If we average the data rates I've seen to 25, then that would indicate
> that an optimize on a 3.5TB is going to take about 39 hours, and might take
> as long as 48 hours.  And if you're running SolrCloud with multiple
> replicas, multiply that by the number of copies of the 3.5TB index.  An
> optimize on a SolrCloud collection handles one shard replica at a time and
> works its way through the entire collection.
> If you are merging different indexes *together*, which a later message
> seems to state, then the actual Lucene operation is probably nearly
> identical, but I'm not really familiar with it, so I cannot say for sure.
> Thanks,
> Shawn

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