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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7276) Limit the number of byte arrays used by DFSOutputStream
Date Fri, 31 Oct 2014 19:39:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14192322#comment-14192322
] 

Tsz Wo Nicholas Sze commented on HDFS-7276:
-------------------------------------------

bq. Can't we simply create those 12 or so managers immediately, and avoid all the "create
a new manager if statistics say so" logic?

ByteArrayManager is a generic class.  So it may not necessarily be 12.

{quote}
174	        wait(1000);

Why does this wait have a timeout? There isn't anything that we're polling here.

...    synchronized int recycle(byte[] array) {
...
	        notifyAll();

Shouldn't this simply be "notify"? There is no point in waking up all waiters, because only
one of them is going to get the buffer we're recycling.
{quote}
Both the wait time out and the notifyAll are for preventing deadlock.  After some thought,
only one of them is needed.  I choose to keep notifyAll since the timeout value is hard to
determine.

> Limit the number of byte arrays used by DFSOutputStream
> -------------------------------------------------------
>
>                 Key: HDFS-7276
>                 URL: https://issues.apache.org/jira/browse/HDFS-7276
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: Tsz Wo Nicholas Sze
>         Attachments: h7276_20141021.patch, h7276_20141022.patch, h7276_20141023.patch,
h7276_20141024.patch, h7276_20141027.patch, h7276_20141027b.patch, h7276_20141028.patch, h7276_20141029.patch,
h7276_20141029b.patch, h7276_20141030.patch
>
>
> When there are a lot of DFSOutputStream's writing concurrently, the number of outstanding
packets could be large.  The byte arrays created by those packets could occupy a lot of memory.



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