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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-16713) Bring back connection caching as a client API
Date Mon, 26 Sep 2016 23:44:20 GMT
Enis Soztutar created HBASE-16713:

             Summary: Bring back connection caching as a client API
                 Key: HBASE-16713
                 URL: https://issues.apache.org/jira/browse/HBASE-16713
             Project: HBase
          Issue Type: New Feature
          Components: Client
            Reporter: Enis Soztutar
             Fix For: 2.0.0, 1.4.0

Connection.getConnection() is removed in master for good reasons. The connection lifecycle
should always be explicit. We have replaced some of the functionality with ConnectionCache
for rest and thrift servers internally, but it is not exposed to clients. 

Turns out our friends doing the hbase-spark connector work needs a similar connection caching
behavior that we have in rest and thrift server. At a higher level we want: 
 - Spark executors should be able to run short living hbase tasks with low latency 
 - Short living tasks should be able to share the same connection, and should not pay the
price of instantiating the cluster connection (which means zk connection, meta cache, 200+
threads, etc)
 - Connections to the cluster should be closed if it is not used for some time. Spark executors
are used for other tasks as well. 
 - Spark jobs may be launched with different configuration objects, possibly connecting to
different clusters between different jobs. 
 - Although not a direct requirement for spark, different users should not share the same
connection object. 

Looking at the old code that we have in branch-1 for {{ConnectionManager}}, managed connections
and the code in ConnectionCache, I think we should do a first-class client level API called
ConnectionCache which will be a hybrid between ConnectionCache and old ConnectionManager.
The lifecycle of the ConnectionCache is still explicit, so I think API-design-wise, this will
fit into the current model. 

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