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From "James Taylor (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-9291) Enable client to setAttribute that is sent once to each region server
Date Wed, 21 Aug 2013 19:24:52 GMT
James Taylor created HBASE-9291:

             Summary: Enable client to setAttribute that is sent once to each region server
                 Key: HBASE-9291
                 URL: https://issues.apache.org/jira/browse/HBASE-9291
             Project: HBase
          Issue Type: New Feature
          Components: IPC/RPC
            Reporter: James Taylor

Currently a Scan and Mutation allow the client to set its own attributes that get passed through
the RPC layer and are accessible from a coprocessor. This is very handy, but breaks down if
the amount of information is large, since this information ends up being sent again and again
to every region. Clients can work around this with an endpoint "pre" and "post" coprocessor
invocation that:
1) sends the information and caches it on the region server in the "pre" invocation
2) invokes the Scan or sends the batch of Mutations, and then
3) removes it in the "post" invocation.
In this case, the client is forced to identify all region servers (ideally, all region servers
that will be involved in the Scan/Mutation), make extra RPC calls, manage the caching of the
information on the region server, age-out the information (in case the client dies before
step (3) that clears the cached information), and must deal with the possibility of a split
occurring while this operation is in-progress.

Instead, it'd be much better if an attribute could be identified as a "region server" attribute
in OperationWithAttributes and the HBase RPC layer would take care of doing the above.

The use case where the above are necessary in Phoenix include:
1) Hash joins, where the results of the smaller side of a join scan are packaged up and sent
to each region server, and
2) Secondary indexing, where the metadata of knowing a) which column family/column qualifier
pairs and b) which part of the row key contributes to which indexes are sent to each region
server that will process a batched put.

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