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https://issues.apache.org/jira/browse/HBASE-2180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12829800#action_12829800
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Andrei Dragomir commented on HBASE-2180:
----------------------------------------
We ran some testing that show improved performance by commenting in the change
in BoundedFileInputStream, by replacing the synchronized statement with the one
commented out, that uses the PositionalReader interface
{noformat}
//synchronized (in) {
// in.seek(pos);
// ret = in.read(b, off, n);
//}
ret = in.read(pos, b, off, n);
{noformat}
> read performance from synchronizing hfile.fddatainputstream
> -----------------------------------------------------------
>
> Key: HBASE-2180
> URL: https://issues.apache.org/jira/browse/HBASE-2180
> Project: Hadoop HBase
> Issue Type: Bug
> Reporter: ryan rawson
> Assignee: ryan rawson
> Fix For: 0.21.0
>
>
> deep in the HFile read path, there is this code:
> synchronized (in) {
> in.seek(pos);
> ret = in.read(b, off, n);
> }
> this makes it so that only 1 read per file per thread is active. this
> prevents the OS and hardware from being able to do IO scheduling by
> optimizing lots of concurrent reads.
> We need to either use a reentrant API (pread may be partially reentrant
> according to Todd) or use multiple stream objects, 1 per scanner/thread.
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