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https://issues.apache.org/jira/browse/SOLR-6832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14337776#comment-14337776
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Otis Gospodnetic commented on SOLR-6832:
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bq. The performance gain increases if coresPerMachine is > 1 and a single JVM
has cores from 'k' shards.
Ever managed to measure how much this feature helps in various scenarios?
bq. For a distributed query, the request is always sent to all the shards even
if the originating SolrCore (handling the original distributed query) is a
replica of one of the shards. If the original Solr-Core can check itself
before sending http requests for any shard, we can probably save some network
hopping and gain some performance.
This sounds as like it saves only a N local calls out of M, where M > N, N is
the number of local replicas that could be queried locally, and M is the total
number of primary shards in the cluster that are to be queries. Is this
correct?
So say there are 20 shards spread evenly over 20 nodes (i.e., 1 shard per node)
and a query request comes in, the node that got the request will query send 19
requests to the remaining 19 nodes and thus save just one network trip by
querying a local shard? I must be missing something...
> Queries be served locally rather than being forwarded to another replica
> ------------------------------------------------------------------------
>
> Key: SOLR-6832
> URL: https://issues.apache.org/jira/browse/SOLR-6832
> Project: Solr
> Issue Type: Bug
> Components: SolrCloud
> Affects Versions: 4.10.2
> Reporter: Sachin Goyal
> Assignee: Timothy Potter
> Fix For: Trunk, 5.1
>
> Attachments: SOLR-6832.patch, SOLR-6832.patch, SOLR-6832.patch,
> SOLR-6832.patch
>
>
> Currently, I see that code flow for a query in SolrCloud is as follows:
> For distributed query:
> SolrCore -> SearchHandler.handleRequestBody() -> HttpShardHandler.submit()
> For non-distributed query:
> SolrCore -> SearchHandler.handleRequestBody() -> QueryComponent.process()
> \\
> \\
> \\
> For a distributed query, the request is always sent to all the shards even if
> the originating SolrCore (handling the original distributed query) is a
> replica of one of the shards.
> If the original Solr-Core can check itself before sending http requests for
> any shard, we can probably save some network hopping and gain some
> performance.
> \\
> \\
> We can change SearchHandler.handleRequestBody() or HttpShardHandler.submit()
> to fix this behavior (most likely the former and not the latter).
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