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https://issues.apache.org/jira/browse/LUCENE-5722?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Robert Muir updated LUCENE-5722:
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Attachment: LUCENE-5722.patch
Patch: warning, its quite ugly but looks correct and seems to do well with
tests (all pass).
I see a combined 45% improvement to docvalues performance with this patch and
LUCENE-5720.
The hairy part: it comes from the fact that even if we have a big file (e.g. dv
.dat today) with multiple buffers, slice() should be optimal in the case only
one is needed to access that region. And I abstracted ByteBufferIndexInput and
i guess i'm paying the cost now :(
On the other hand this opens up additional things to explore, e.g. maybe we
should override readByte/Bytes since its much less code to inline in this case,
and maybe we should investigate simply changing directpackedreaders to just
require a slice over their data (e.g. getFilePointer == 0) to remove the
addition there.
> Speed up MMapDirectory.seek()
> -----------------------------
>
> Key: LUCENE-5722
> URL: https://issues.apache.org/jira/browse/LUCENE-5722
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Robert Muir
> Attachments: LUCENE-5722.patch
>
>
> For traditional lucene access which is mostly sequential, occasional
> advance(), I think this method gets drowned out in noise.
> But for access like docvalues, its important. Unfortunately seek() is complex
> today because of mapping multiple buffers.
> However, the very common case is that only one map is used for a given clone
> or slice.
> When there is the possibility to use only a single mapped buffer, we should
> instead take advantage of ByteBuffer.slice(), which will adjust the internal
> mmap address and remove the offset calculation. furthermore we don't need the
> shift/mask or even the negative check, as they are then all handled with the
> ByteBuffer api: seek is a one-liner (with try/catch of course to convert
> exceptions).
> This makes docvalues access 20% faster, I havent tested conjunctions or
> anyhting like that.
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