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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2975) MMapDirectory on chunk size boundaries broken
Date Sat, 19 Mar 2011 00:05:29 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13008691#comment-13008691
] 

Robert Muir commented on LUCENE-2975:
-------------------------------------

The hotspot bug happens in a pretty crappy place to tell you the truth, readVint()

I know this because if i make a 'stupid' readVint like this:
{noformat}
    @Override
    public int readVInt() throws IOException {
      byte scratch[] = new byte[1];
      readBytes(scratch, 0, 1);
      byte b = scratch[0];
      int i = b & 0x7F;
      for (int shift = 7; (b & 0x80) != 0; shift += 7) {
        readBytes(scratch, 0, 1);
        b = scratch[0];
        i |= (b & 0x7F) << shift;
      }
      return i;
    }
{noformat}

then it avoids the bug. so i guess the trick would be to make one thats just as fast as what
we have now, but still avoids the bug.


> MMapDirectory on chunk size boundaries broken
> ---------------------------------------------
>
>                 Key: LUCENE-2975
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2975
>             Project: Lucene - Java
>          Issue Type: Bug
>    Affects Versions: 3.1
>            Reporter: Uwe Schindler
>            Priority: Blocker
>             Fix For: 3.1
>
>
> When testing the 3.1-RC1 made by Yonik on the PANGAEA (www.pangaea.de) productive system
I figured out that suddenly on a large segment (about 5 GiB) some stored fiels suddenly produce
a strange deflate decompression problem (CompressionTools) although the stored fields are
no longer pre-3.0 compressed. It seems that the header of the stored field is read incorrectly
at the buffer boundary in MultiMMapDir and then FieldsReader just incorrectly detects a deflate-compressed
field (CompressionTools).
> The error occurs reproducible on CheckIndex with MMapDirectory, but not with NIODir or
SimpleDir. The FDT file of that segment is 2.6 GiB, on Solaris the chunk size is Integer.MAX_VALUE,
so we have 2 MultiMMap IndexInputs.
> Robert and me have the index ready as a tar file, we will do tests on our local machines
and hopefully solve the bug, maybe introduced by Robert's recent changes to MMap.

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