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From "Karthick Sankarachary (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-2937) Facilitate Timeouts In HBase Client
Date Fri, 27 Aug 2010 00:53:55 GMT
Facilitate Timeouts In HBase Client

                 Key: HBASE-2937
                 URL: https://issues.apache.org/jira/browse/HBASE-2937
             Project: HBase
          Issue Type: New Feature
          Components: client
    Affects Versions: 0.89.20100621
            Reporter: Karthick Sankarachary
             Fix For: 0.89.20100621

Currently, there is no way to force an operation on the HBase client (viz. HTable) to time
out if a certain amount of time has elapsed.  In other words, all invocations on the HTable
class are veritable blocking calls, which will not return until a response (successful or
otherwise) is received. 

In general, there are two ways to handle timeouts:  (a) call the operation in a separate thread,
until it returns a response or the wait on the thread times out and (b) have the underlying
socket unblock the operation if the read times out.  The downside of the former approach is
that it consumes more resources in terms of threads and callables. 

Here, we describe a way to specify and handle timeouts on the HTable client, which relies
on the latter approach (i.e., socket timeouts). Right now, the HBaseClient sets the socket
timeout to the value of the "ipc.ping.interval" parameter, which is also how long it waits
before pinging the server in case of a failure. The goal is to allow clients to set that timeout
on the fly through HTable. Rather than adding an optional timeout argument to every HTable
operation, we chose to make it a property of HTable which effectively applies to every method
that involves a remote operation.

In order to propagate the timeout  from HTable to HBaseClient, we replaced all occurrences
of ServerCallable in HTable with an extension called ClientCallable, which sets the timeout
on the region server interface, once it has been instantiated, through the HConnection object.
The latter, in turn, asks HBaseRPC to pass that timeout to the corresponding Invoker, so that
it may inject the timeout at the time the invocation is made on the region server proxy. Right
before the request is sent to the server, we set the timeout specified by the client on the
underlying socket.

In conclusion, this patch will afford clients the option of performing an HBase operation
until it completes or a specified timeout elapses. Note that a timeout of zero is interpreted
as an infinite timeout.

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