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From "Eshcar Hillel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13071) Hbase Streaming Scan Feature
Date Tue, 03 Mar 2015 22:52:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13071?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14345929#comment-14345929

Eshcar Hillel commented on HBASE-13071:

Thanks [~stack] for your comments, I applied most of them.

  ** The cache is defined in the context of ClientScanner, therefore initializing it and the
prefetch methods are defined here.
IMHO, the entire hierarchy requires major refactoring (e.g., due to code replication), but
this should be done in the scope of a different jira :).
  ** How would you suggest to get a hold of the thread executing the prefetch, so as to interrupt
it on close?
  ** Apologies for the formatting irregularities. I use IntelliJ which fails to import the
eclipse formatting as suggested in the help page you referred me to.
  ** Waiting (patiently) for the pictures...

> Hbase Streaming Scan Feature
> ----------------------------
>                 Key: HBASE-13071
>                 URL: https://issues.apache.org/jira/browse/HBASE-13071
>             Project: HBase
>          Issue Type: New Feature
>    Affects Versions: 0.98.11
>            Reporter: Eshcar Hillel
>         Attachments: HBASE-13071_98_1.patch, HBASE-13071_trunk_1.patch, HBASE-13071_trunk_2.patch,
HBASE-13071_trunk_3.patch, HBASE-13071_trunk_4.patch, 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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