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https://issues.apache.org/jira/browse/HBASE-13071?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14513647#comment-14513647
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Edward Bortnikov commented on HBASE-13071:
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I'd suggest leaving the use of this feature manual rather than expecting the
system to auto-tune. It is often hard to know whether the application requires
aggressive caching at the client side. For example, consider an application
that does some tricky aggregation of the scanned data, in which the compute
part is considerable. There is no way for HBase to know that in advance. The
optimization does not come for free (up to 2x caching at the client side), so
IMHO it's up to the application to decide whether to use it.
Dear community - could you please review and vote on the last patch before it
becomes obsolete again? The JIRA is still not assigned to any committer.
> 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: 99.eshcar.png, HBASE-13071_98_1.patch,
> HBASE-13071_trunk_1.patch, HBASE-13071_trunk_10.patch,
> HBASE-13071_trunk_2.patch, HBASE-13071_trunk_3.patch,
> HBASE-13071_trunk_4.patch, HBASE-13071_trunk_5.patch,
> HBASE-13071_trunk_6.patch, HBASE-13071_trunk_7.patch,
> HBASE-13071_trunk_8.patch, HBASE-13071_trunk_9.patch,
> HBASE-13071_trunk_rebase_1.0.patch, HBaseStreamingScanDesign.pdf,
> HbaseStreamingScanEvaluation.pdf,
> HbaseStreamingScanEvaluationwithMultipleClients.pdf, gc.delay.png,
> gc.eshcar.png, gc.png, hits.delay.png, hits.eshcar.png, hits.png,
> latency.delay.png, latency.png, network.png
>
>
> 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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