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https://issues.apache.org/jira/browse/HBASE-26273?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Josh Elser updated HBASE-26273:
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Release Note: HBase's MapReduce API which can operate over HBase snapshots
will now default to using ReadType.STREAM instead of ReadType.DEFAULT (which is
PREAD) as a result of this change. HBase developers expect that STREAM will
perform significantly better for average Snapshot-based batch jobs. Users can
restore the previous functionality (using PREAD) by updating their code to
explicitly set a value of `ReadType.PREAD` on the `Scan` object they provide to
TableSnapshotInputFormat, or by setting the configuration property
"hbase.TableSnapshotInputFormat.scanner.readtype" to "PREAD" in hbase-site.xml.
> TableSnapshotInputFormat/TableSnapshotInputFormatImpl should use
> ReadType.STREAM for scanning HFiles
> -----------------------------------------------------------------------------------------------------
>
> Key: HBASE-26273
> URL: https://issues.apache.org/jira/browse/HBASE-26273
> Project: HBase
> Issue Type: Improvement
> Components: mapreduce
> Affects Versions: 3.0.0-alpha-1, 2.4.6
> Reporter: Tak-Lon (Stephen) Wu
> Assignee: Josh Elser
> Priority: Major
> Fix For: 2.5.0, 3.0.0-alpha-2, 2.4.7
>
>
> After the change in HBASE-17917 that use PREAD ({{ReadType.DEFAULT}}) for all
> user scan, the behavior of TableSnapshotInputFormat changed from STREAM to
> PREAD.
> TableSnapshotInputFormat is supposed to be use with a YARN/MR or other batch
> engine that should read the entire HFile in the container/executor, with
> default always to PREAD, we executing a lot more DFSInputStream#seek calls to
> simply read through the datablock section of the HFile.
> The goal of this change is to make any downstream using
> TableSnapshotInputFormat with STREAM scan.
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