James Taylor created HBASE-9291:
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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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