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https://issues.apache.org/jira/browse/PHOENIX-4278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16360488#comment-16360488
 ] 

ASF GitHub Bot commented on PHOENIX-4278:
-----------------------------------------

Github user ohadshacham commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/291#discussion_r167501024
  
    --- Diff: 
phoenix-core/src/main/java/org/apache/phoenix/query/ConnectionQueryServicesImpl.java
 ---
    @@ -850,19 +849,12 @@ private void addCoprocessors(byte[] tableName, 
HTableDescriptor descriptor, PTab
                         && !SchemaUtil.isMetaTable(tableName)
                         && !SchemaUtil.isStatsTable(tableName)) {
                     if (isTransactional) {
    -                    if 
(!descriptor.hasCoprocessor(PhoenixTransactionalIndexer.class.getName())) {
    -                        
descriptor.addCoprocessor(PhoenixTransactionalIndexer.class.getName(), null, 
priority, null);
    -                    }
    --- End diff --
    
    Let's skip this for now and add a release note. 


> Implement pure client side transactional index maintenance
> ----------------------------------------------------------
>
>                 Key: PHOENIX-4278
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4278
>             Project: Phoenix
>          Issue Type: Improvement
>            Reporter: James Taylor
>            Assignee: Ohad Shacham
>            Priority: Major
>         Attachments: PHOENIX-4278.4.x-HBase-1.3.v1.patch
>
>
> The index maintenance for transactions follows the same model as non 
> transactional tables - coprocessor based on data table updates that looks up 
> previous row value to perform maintenance. This is necessary for non 
> transactional tables to ensure the rows are locked so that a consistent view 
> may be obtained. However, for transactional tables, the time stamp oracle 
> ensures uniqueness of time stamps (via transaction IDs) and the filtering 
> handles a scan seeing the "true" last committed value for a row. Thus, 
> there's no hard dependency to perform this on the server side.
> Moving the index maintenance to the client side would prevent any RS->RS RPC 
> calls (which have proved to be troublesome for HBase). It would require 
> returning more data to the client (i.e. the prior row value), but this seems 
> like a reasonable tradeoff.



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