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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Updated: (LUCENE-1044) Behavior on hard power shutdown
Date Tue, 27 Nov 2007 20:15:43 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-1044?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael McCandless updated LUCENE-1044:
---------------------------------------

    Attachment: LUCENE-1044.take4.patch

OK I did a simplistic patch (attached) whereby FSDirectory has a
background thread that re-opens, syncs, and closes those files that
Lucene has written.  (I'm using a modified version of the class from
Doron's test).

This patch is nowhere near ready to commit; I just coded up enough so
we could get a rough measure of performance cost of syncing.  EG we
must prevent deletion of a commit point until a future commit point is
fully sync'd to stable storage; we must also take care not to sync a
file that has been deleted before we sync'd it; don't sync until the
end when running with autoCommit=false; merges if run by
ConcurrentMergeScheduler should [maybe] sync in the foreground; maybe
forcefully throttle back updates if syncing is falling too far behind;
etc.

I ran the same alg as the tests above (index first 150K docs of
Wikipedia).  I ran CFS and no CFS X sync and nosync (4 tests) for each
IO system.  Time is the fastest of 2 runs:

|| IO System || CFS sync || CFS nosync || CFS % slower || non-CFS sync || non-CFS nosync ||
non-CFS % slower ||
| ReiserFS 6-drive RAID5 array Linux (2.6.22.1) | 188 | 157 | 19.7% | 143 | 147 | -2.7% |
| EXT3 single internal drive Linux (2.6.22.1) | 173 | 157 | 10.2% | 136 | 132 | 3.0% |
| 4 drive RAID0 array Mac Pro (10.4 Tiger) | 153 | 152 | 0.7% | 150 | 149 | 0.7% |
| Win XP Pro laptop, single drive | 463 | 352 | 31.5% | 343 | 335 | 2.4% |
| Mac Pro single external drive | 463 | 352 | 31.5% | 343 | 335 | 2.4% |

The good news is, the non-CFS case shows very little cost when we do
BG sync'ing!

The bad news is, the CFS case still shows a high cost.  However, by
not sync'ing the files that go into the CFS (and also not committing a
new segments_N file until after the CFS is written) I expect that cost
to go way down.

One caveat: I'm using a 8 MB RAM buffer for all of these tests.  As
Yonik pointed out, if you have a smaller buffer, or, you add just a
few docs and then close your writer, the sync cost as a pctg of net
indexing time will be quite a bit higher.


> Behavior on hard power shutdown
> -------------------------------
>
>                 Key: LUCENE-1044
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1044
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Index
>         Environment: Windows Server 2003, Standard Edition, Sun Hotspot Java 1.5
>            Reporter: venkat rangan
>            Assignee: Michael McCandless
>             Fix For: 2.3
>
>         Attachments: FSyncPerfTest.java, LUCENE-1044.patch, LUCENE-1044.take2.patch,
LUCENE-1044.take3.patch, LUCENE-1044.take4.patch
>
>
> When indexing a large number of documents, upon a hard power failure  (e.g. pull the
power cord), the index seems to get corrupted. We start a Java application as an Windows Service,
and feed it documents. In some cases (after an index size of 1.7GB, with 30-40 index segment
.cfs files) , the following is observed.
> The 'segments' file contains only zeros. Its size is 265 bytes - all bytes are zeros.
> The 'deleted' file also contains only zeros. Its size is 85 bytes - all bytes are zeros.
> Before corruption, the segments file and deleted file appear to be correct. After this
corruption, the index is corrupted and lost.
> This is a problem observed in Lucene 1.4.3. We are not able to upgrade our customer deployments
to 1.9 or later version, but would be happy to back-port a patch, if the patch is small enough
and if this problem is already solved.

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