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https://issues.apache.org/jira/browse/HBASE-25582?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17298615#comment-17298615
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Anoop Sam John commented on HBASE-25582:
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Thanks for the reviews [~zhangduo] and [~vjasani]. Pushed to branch-2.3+
branches
> Support setting scan ReadType to be STREAM at cluster level
> -----------------------------------------------------------
>
> Key: HBASE-25582
> URL: https://issues.apache.org/jira/browse/HBASE-25582
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 2.0.0
> Reporter: Anoop Sam John
> Assignee: Anoop Sam John
> Priority: Major
> Fix For: 3.0.0-alpha-1, 2.5.0, 2.3.5, 2.4.2
>
>
> We have the config 'hbase.storescanner.use.pread' at cluster level to set
> ReadType to be PRead if not explicitly specified in Scan object.
> Same way we can have a way to make scan as STREAM type at cluster level (if
> not specified at Scan object level)
> We do not need any new configs or so. We have the config
> 'hbase.storescanner.pread.max.bytes' which specifies when to switch read type
> to stream and it defaults to 4 * HFile block size. If one config this value
> as <= 0 means user need the switch when scanner is created itself. With such
> a handling we can support it.
> So every scan need not set the read type.
> The issue is in Cloud storage based system using Stream reads might be
> better. We introduced this PRead based scan with tests on HDFS based
> storage. In my customer case, Azure storage in place and WASB driver been
> used. We have a read ahead mechanism there (Read an entire Block of a blob in
> one REST call) and buffer that in WASB driver. This helps a lot wrt longer
> scans. Ya with config 'hbase.storescanner.pread.max.bytes' we can make the
> switch to happen early but better to go with 1.x way where the scan starts
> with Stream read itself.
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