[ http://issues.apache.org/jira/browse/LUCENE-554?page=comments#action_12412315 ]
Patrick Kimber commented on LUCENE-554: --------------------------------------- This patch is exactly what we require. Our Lucene index often becomes unusable when the "segments.new" file is not renamed to "segments". We would be very happy to test the patch before you publish it. > Possible index corruption if crashing while replacing segments file > ------------------------------------------------------------------- > > Key: LUCENE-554 > URL: http://issues.apache.org/jira/browse/LUCENE-554 > Project: Lucene - Java > Type: Bug > Components: Index > Versions: 1.9 > Reporter: Nadav Har'El > Priority: Minor > > Lucene's indexing is expected to be reasonably tolerant to computer crashes > or the indexing process being killed. By reasonably tolerant, I mean that it > is ok to lose a few documents (those currently buffered in memory), or have > to repeat some work (e.g., a long merge that was in progress) - but it is not > ok for the entire index, or large chunks of it, to become irreversebly > corrupt. > The fact that Lucene works by repeated merging of several small segments into > a new larger segments, solves most of the crash problems, because until the > new segment is fully created, the old segments are still there and fully > functional. However, one possibility for corruption remains in the segment > replacement code: > After a new segment is created, a new segments file is written as a new file > "segments.new", and then this file is renamed to "segments". The problem is > that this renaming is done using Directory.renameFile(), and > FSDirectory.renameFile is *NOT* atomic: it first deletes the old file, and > then renames the new file. A crash between these stages (or perhaps during > Java's rename which also isn't guaranteed to be atomic) will potentially > leave us without a working "segments" file. > I will post here a patch for this bug shortly. > The patch will also include a change to Directory.renameFile()'s Javadoc. It > currently claims "This replacement should be atomic.", which is false in > FSDirectory. Instead it should make a weaker claim, for example > "This replacement does not have to be atomic, but must at least obey a > weaker guarantee: at any time during the replacement, either the "from" file > is still available, or the "to" file is available with either the new or old > content." > (or, we can just drop the guaranteee altogether, like Java's File.renameTo() > provides no atomic-ness guarantees). -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
