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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2537) FSDirectory.copy() impl is unsafe
Date Sun, 25 Jul 2010 05:58:49 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2537?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12892073#action_12892073
] 

Shai Erera commented on LUCENE-2537:
------------------------------------

If there are no objections, I'll commit this today,

> FSDirectory.copy() impl is unsafe
> ---------------------------------
>
>                 Key: LUCENE-2537
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2537
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Store
>            Reporter: Shai Erera
>            Assignee: Shai Erera
>             Fix For: 3.1, 4.0
>
>         Attachments: FileCopyTest.java, LUCENE-2537.patch, LUCENE-2537.patch
>
>
> There are a couple of issues with it:
> # FileChannel.transferFrom documents that it may not copy the number of bytes requested,
however we don't check the return value. So need to fix the code to read in a loop until all
bytes were copied..
> # When calling addIndexes() w/ very large segments (few hundred MBs in size), I ran into
the following exception (Java 1.6 -- Java 1.5's exception was cryptic):
> {code}
> Exception in thread "main" java.io.IOException: Map failed
>     at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:770)
>     at sun.nio.ch.FileChannelImpl.transferToTrustedChannel(FileChannelImpl.java:450)
>     at sun.nio.ch.FileChannelImpl.transferTo(FileChannelImpl.java:523)
>     at org.apache.lucene.store.FSDirectory.copy(FSDirectory.java:450)
>     at org.apache.lucene.index.IndexWriter.addIndexes(IndexWriter.java:3019)
> Caused by: java.lang.OutOfMemoryError: Map failed
>     at sun.nio.ch.FileChannelImpl.map0(Native Method)
>     at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:767)
>     ... 7 more
> {code}
> I changed the impl to something like this:
> {code}
> long numWritten = 0;
> long numToWrite = input.size();
> long bufSize = 1 << 26;
> while (numWritten < numToWrite) {
>   numWritten += output.transferFrom(input, numWritten, bufSize);
> }
> {code}
> And the code successfully adds the indexes. This code uses chunks of 64MB, however that
might be too large for some applications, so we definitely need a smaller one. The question
is how small so that performance won't be affected, and it'd be great if we can let it be
configurable, however since that API is called by other API, such as addIndexes, not sure
it's easily controllable.
> Also, I read somewhere (can't remember now where) that on Linux the native impl is better
and does copy in chunks. So perhaps we should make a Linux specific impl?

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