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https://issues.apache.org/jira/browse/HBASE-13071?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14332166#comment-14332166
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Eshcar Hillel commented on HBASE-13071:
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Thanks all for your comments.
@stack, I wasn't aware of the discussions in the other Jiras, thanks for
putting the links -- I am now updated.
@ Lars, the concurrent queue in the suggested modification is implemented as a
LinkedBlockingQueue (which in addition to efficient put and get operations
provides an efficient count operation). But we can discuss alternatives,
including devising a dedicated data structure if it looks this can improve
performance.
The suggested modification focuses on managing the concurrent queue at the
client side, but still applies the "pull" model, where the client pulls the
data from the server.
To support a true streaming, a push model, where the server is pushing the data
to the client, might be better.
In both cases a concurrent queue is part of the solution.
I am attaching some evaluation results.
Next step is to provide a patch for 0.98.
> Hbase Streaming Scan Feature
> ----------------------------
>
> Key: HBASE-13071
> URL: https://issues.apache.org/jira/browse/HBASE-13071
> Project: HBase
> Issue Type: New Feature
> Reporter: Eshcar Hillel
> Attachments: HBaseStreamingScanDesign.pdf,
> HbaseStreamingScanEvaluation.pdf
>
>
> A scan operation iterates over all rows of a table or a subrange of the
> table. The synchronous nature in which the data is served at the client side
> hinders the speed the application traverses the data: it increases the
> overall processing time, and may cause a great variance in the times the
> application waits for the next piece of data.
> The scanner next() method at the client side invokes an RPC to the
> regionserver and then stores the results in a cache. The application can
> specify how many rows will be transmitted per RPC; by default this is set to
> 100 rows.
> The cache can be considered as a producer-consumer queue, where the hbase
> client pushes the data to the queue and the application consumes it.
> Currently this queue is synchronous, i.e., blocking. More specifically, when
> the application consumed all the data from the cache --- so the cache is
> empty --- the hbase client retrieves additional data from the server and
> re-fills the cache with new data. During this time the application is blocked.
> Under the assumption that the application processing time can be balanced by
> the time it takes to retrieve the data, an asynchronous approach can reduce
> the time the application is waiting for data.
> We attach a design document.
> We also have a patch that is based on a private branch, and some evaluation
> results of this code.
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