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From "Yonik Seeley" <yo...@apache.org>
Subject Re: [jira] Resolved: (LUCENE-1044) Behavior on hard power shutdown
Date Sun, 04 Nov 2007 14:30:17 GMT
On 11/4/07, Michael McCandless <lucene@mikemccandless.com> wrote:
> The problem is, on a hard shutdown (kill -9 or JVM/machine crashes),
> apparently future operations may have completed while some past
> operations have not.  For example, the new segments_N file was
> successfully written while say the _X.fdx file of the just-flushed
> segment was not successfully written, even though Lucene had written &
> closed _X.fdx before segments_N.

That should be impossible except for a machine crash.  Kill -9 or a
JVM crash should have no effect on data already written.

But a sync option would be both simple and useful for people trying to
take live snapshots of an index, or to protect against machine
crashes.  This isn't an absolute 100% guarantee either (so don't test
for it) - the drives often lie to the OS about data being flushed.
It's the best we can do at our level though.
http://www.google.com/search?q=fsync+drive+lies

-Yonik

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