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https://issues.apache.org/jira/browse/LUCENE-3218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13087723#comment-13087723
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Uwe Schindler commented on LUCENE-3218:
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bq. i think we should prevent the seek if not absolutely necessary.
You have a very small optimization here that only affects opening the CFS.
But because we need to fix the wrong behaviour in FileSwitch (and also
NRTCaching dir, which is in my opinion more serious!!!!), FileSwitch and
NRTCachingDir now use the default CompoundFileImpl. If you wrap MMapDir by
FileSwitch or NRTCaching, the whole custom impl of the compound file in MMap
that speeds up even further is obsolete, as not used (you can use the compound
file with really no slowdown at all as we can map parts of the CFS file into
memeory and need no offset calculations and can also save mapping costs).
This is gone now, just because a one-time seek at opening time is prevented.
> Make CFS appendable
> ---------------------
>
> Key: LUCENE-3218
> URL: https://issues.apache.org/jira/browse/LUCENE-3218
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/index
> Affects Versions: 4.0
> Reporter: Simon Willnauer
> Assignee: Simon Willnauer
> Fix For: 3.4, 4.0
>
> Attachments: LUCENE-3218.patch, LUCENE-3218.patch, LUCENE-3218.patch,
> LUCENE-3218.patch, LUCENE-3218_3x.patch, LUCENE-3218_test_fix.patch,
> LUCENE-3218_tests.patch
>
>
> Currently CFS is created once all files are written during a flush / merge.
> Once on disk the files are copied into the CFS format which is basically a
> unnecessary for some of the files. We can at any time write at least one file
> directly into the CFS which can save a reasonable amount of IO. For instance
> stored fields could be written directly during indexing and during a Codec
> Flush one of the written files can be appended directly. This optimization is
> a nice sideeffect for lucene indexing itself but more important for DocValues
> and LUCENE-3216 we could transparently pack per field files into a single
> file only for docvalues without changing any code once LUCENE-3216 is
> resolved.
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