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https://issues.apache.org/jira/browse/SOLR-12642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17094072#comment-17094072
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Cao Manh Dat commented on SOLR-12642:
-------------------------------------

Above numbers are not correct. Basically above benchmark was performed on a 
buggy Jetty version. During indexing, leader failed to send updates to replicas 
quite frequently without networking issue, therefore replicas were put into 
recovery mode. Replicas did not do indexing much so that result the gain in CPU 
time and garbage generated. On Leader's side the CPU time is 50% more since it 
need to stream index files back to replicas during recovery.

> SolrCmdDistributor should send updates in batch when use Http2SolrClient?
> -------------------------------------------------------------------------
>
>                 Key: SOLR-12642
>                 URL: https://issues.apache.org/jira/browse/SOLR-12642
>             Project: Solr
>          Issue Type: Improvement
>            Reporter: Cao Manh Dat
>            Assignee: Cao Manh Dat
>            Priority: Major
>             Fix For: 8.0
>
>         Attachments: http2-branch.log, master-branch.log
>
>
> In the past, batch updates are sent in a single stream from the leader, the 
> replica will create a single thread to parse all the updates. For the 
> simplicity of {{SOLR-12605}}, the leader is now sending individual updates to 
> replicas, therefore they are now parsing updates in different threads which 
> increase the usage of memory and CPU.
> In the past, this is an unacceptable approach, because, for every update, we 
> must create different connections to replicas. But with the support of 
> HTTP/2, all updates will be sent in a single connection from leader to a 
> replica. Therefore the cost is not as high as it used to be.
> On the other hand, sending individual updates will improve the indexing 
> performance and better error-handling for failures of a single update in a 
> batch.



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