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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18055) HBASE-17917 closes the scanners while a scan is in progess for switching over to stream reads
Date Tue, 16 May 2017 07:06:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18055?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16011857#comment-16011857

Anoop Sam John commented on HBASE-18055:

So Duo, what happens on this pread / stream read is that, now by default all read requests
use pread and we will switch from it when the read is doing many consecutive cells read. Correct?
 May be the switch we should do only after the current RPC?  Or we should at least return
back the result before doing the switch and open new scanner?

> HBASE-17917 closes the scanners while a scan is in progess for switching over to stream
> ---------------------------------------------------------------------------------------------
>                 Key: HBASE-18055
>                 URL: https://issues.apache.org/jira/browse/HBASE-18055
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver, Scanners
>    Affects Versions: 2.0.0
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>             Fix For: 2.0.0
> In HBASE-17917 tries to switch from pread to stream read when a specific size of bytes
are read. So in order to switch over, it closes the existing scanners and creates a new scanners
with pread=false.
> When we close the exisitng scanners - if the blocks are served from offheap cache we
will decrement the ref count on those blocks and if it becomes zero we make the block ready
for eviction. Then there is a chance that the result could be corrupted if new blocks occupy
the cache. So the expectation was that till the RPC call completes the response we will hold
on to the blocks that are referred by the scan. (except the last one). So trying to switch
over to stream read will break this expectation and hence TestBlockEvictionfromclient fails.

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