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https://issues.apache.org/jira/browse/HDFS-6698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14072305#comment-14072305
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stack commented on HDFS-6698:
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bq. Changing the locking model for the DFSInputStream seems like a big project.
[~cmccabe] The patch attached here seems to respect the existing locking model
and conditions that prefix length calculations. Or are you thinking that we
close this issue and do all synchronization changes in HDFS-6735, all in the
one go? Thanks.
> try to optimize DFSInputStream.getFileLength()
> ----------------------------------------------
>
> Key: HDFS-6698
> URL: https://issues.apache.org/jira/browse/HDFS-6698
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: hdfs-client
> Affects Versions: 3.0.0
> Reporter: Liang Xie
> Assignee: Liang Xie
> Attachments: HDFS-6698.txt, HDFS-6698.txt
>
>
> HBase prefers to invoke read() serving scan request, and invoke pread()
> serving get reqeust. Because pread() almost holds no lock.
> Let's image there's a read() running, because the definition is:
> {code}
> public synchronized int read
> {code}
> so no other read() request could run concurrently, this is known, but pread()
> also could not run... because:
> {code}
> public int read(long position, byte[] buffer, int offset, int length)
> throws IOException {
> // sanity checks
> dfsClient.checkOpen();
> if (closed) {
> throw new IOException("Stream closed");
> }
> failures = 0;
> long filelen = getFileLength();
> {code}
> the getFileLength() also needs lock. so we need to figure out a no lock impl
> for getFileLength() before HBase multi stream feature done.
> [~saint....@gmail.com]
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