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https://issues.apache.org/jira/browse/LUCENE-5857?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14079123#comment-14079123
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Ramkumar Aiyengar commented on LUCENE-5857:
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bq. It's somewhat dangerous to add this logic to try up to N commits backwards,
e.g. in an app that saves multiple commit points, this could silently lose data
if there is a transient IOException loading the "true" segments_N file. It's
already spooky enough that Lucene tries up to N commits forwards...
We had initially considered trying up to N commits backwards but not going
behind {{segments.gen}}.
The application has a very short soft commit interval (125ms) and a longer hard
commit. Couldn't it happen that there was a soft commit, and the following hard
commit was interrupted? See SOLR-6296 for the stack which was interrupted by
Solr, IW.close was interrupted during fsync, that would have tried to sync two
segments_N files right?
> make genLookaheadCountLimit configurable, add genLookbackCountLimit parameter
> -----------------------------------------------------------------------------
>
> Key: LUCENE-5857
> URL: https://issues.apache.org/jira/browse/LUCENE-5857
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Christine Poerschke
>
> The problem we saw was that an error-in-final-commit during solr-shutdown led
> to a corrupted segments_.... file which prevented subsequent solr-start,
> details below.
> this change:
> * adds genLookbackCountLimit similar to the existing genLookaheadCountLimit
> * makes both parameters configurable (initial values defaulted to existing
> behaviour)
> error-in-final-commit result:
> * segments_2fi5 file present and zero-bytes long
> (https://issues.apache.org/jira/i#browse/SOLR-6296 concerns root cause)
> * segments_2fi4 file absent on disk (speculation: 2fi4 was result of
> in-memory segment merging)
> * segments_2fi3 file present and usable (but not found by existing
> looking-logic)
> * segments.gen file referenced 2fi3
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