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https://issues.apache.org/jira/browse/PHOENIX-6385?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Viraj Jasani reassigned PHOENIX-6385:
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Assignee: Viraj Jasani (was: Anoop Sam John)
> Not to use Scan#setSmall for HBase 2.x versions
> -----------------------------------------------
>
> Key: PHOENIX-6385
> URL: https://issues.apache.org/jira/browse/PHOENIX-6385
> Project: Phoenix
> Issue Type: Improvement
> Reporter: Anoop Sam John
> Assignee: Viraj Jasani
> Priority: Major
>
> {code:java}
> /**
> * Set whether this scan is a small scan
> * <p>
> * Small scan should use pread and big scan can use seek + read seek + read
> is fast but can cause
> * two problem (1) resource contention (2) cause too much network io
> [89-fb] Using pread for
> * non-compaction read request
> https://issues.apache.org/jira/browse/HBASE-7266 On the other hand,
> * if setting it true, we would do openScanner,next,closeScanner in one RPC
> call. It means the
> * better performance for small scan. [HBASE-9488]. Generally, if the scan
> range is within one
> * data block(64KB), it could be considered as a small scan.
> * @param small
> * @deprecated since 2.0.0 and will be removed in 3.0.0. Use {@link
> #setLimit(int)} and
> * {@link #setReadType(ReadType)} instead. And for the one rpc
> optimization, now we will also
> * fetch data when openScanner, and if the number of rows reaches the
> limit then we will close
> * the scanner automatically which means we will fall back to one rpc.
> * @see #setLimit(int)
> * @see #setReadType(ReadType)
> * @see <a
> href="https://issues.apache.org/jira/browse/HBASE-17045";>HBASE-17045</a>
> */
> @Deprecated
> public Scan setSmall(boolean small)
> {code}
> In 1.x there is seperate ClientSmallScanner impl doing single RPC for scan.
> In 2.x by default it handles single RPC if there are less number of rows.
> We might have to setLimit.
> Also in 2.x setSmall() API sets the readType to be PRead. But this is good
> for small reads like only one hfile blocks get read. But what I noticed in
> phoenix is that even count(*) query result in setting Scan as small scan and
> end up using PRead (This will result in full scan).
> So we should not be setting the ReadType at all. Instead rely on HBase to
> intelligently switch scan type (start with PRead and if it scans more data
> switch to stream read)
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