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https://issues.apache.org/jira/browse/SOLR-2592?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529248#comment-13529248
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Yonik Seeley commented on SOLR-2592:
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So with the composite key hashing strategy of using the first part of the ID as
the upper bits (what I've started calling a hash domain) and the second part
the lower bits, one needed to use an initial numShards equal to a power of two
*if* one wanted to absolutely avoid a hash domain from being split over more
than one shard. For most people, this wouldn't be an issue - you only need to
guarantee splitting domains if you're using a feature that doesn't work across
shards (like pseudo-join for example).
I just checked in a change to remove that limitation. You can now use any
numShards and the resulting shard ranges will be rounded to the nearest hash
domain to avoid splitting them (this amounts to a maximum size rounding error
of 1/65536th of the hash ring, or 0.002%).
> Custom Hashing
> --------------
>
> Key: SOLR-2592
> URL: https://issues.apache.org/jira/browse/SOLR-2592
> Project: Solr
> Issue Type: New Feature
> Components: SolrCloud
> Affects Versions: 4.0-ALPHA
> Reporter: Noble Paul
> Assignee: Yonik Seeley
> Fix For: 4.1
>
> Attachments: dbq_fix.patch, pluggable_sharding.patch,
> pluggable_sharding_V2.patch, SOLR-2592.patch, SOLR-2592_progress.patch,
> SOLR-2592_query_try1.patch, SOLR-2592_r1373086.patch,
> SOLR-2592_r1384367.patch, SOLR-2592_rev_2.patch,
> SOLR_2592_solr_4_0_0_BETA_ShardPartitioner.patch
>
>
> If the data in a cloud can be partitioned on some criteria (say range, hash,
> attribute value etc) It will be easy to narrow down the search to a smaller
> subset of shards and in effect can achieve more efficient search.
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