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From "Karthick Sankarachary (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2937) Facilitate Timeouts In HBase Client
Date Sun, 02 Jan 2011 21:42:46 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2937?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12976563#action_12976563

Karthick Sankarachary commented on HBASE-2937:

Hi Stack,

The interruptible client logic has been rewritten in such a way as to allow:

a) A timeout to be specified at the operation-level, which surrounds the block of code that
instantiates the server (proxy) as well as the invocation on that proxy. Specifically, this
was implemented by submitting the operation as a task to a different thread and then waiting
on its future object.
b) A timeout to be specified at the call-level, which only includes the invocation on the
server proxy object. Specifically, this was implemented by setting a timeout on the wait method
that the HBaseClient invokes on the call object.
c) A retry logic to be specified at the call-level, which dictates how many times, if at all,
the call should be retried, in the event of a call-level timeout.

For each of the above behaviors, corresponding configuration settings have been made available
(see TimeoutPolicy for details). 

Last but not the least, a test case (viz. TestFromClientSide#testTimeouts) was added which
illustrates the various ways in which timeouts may be used.

I look forward to your comments.


> 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
>            Assignee: Karthick Sankarachary
>            Priority: Critical
>             Fix For: 0.92.0
>         Attachments: HBASE-2937.patch, HBASE-2937.patch
> 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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