[jira] [Updated] (LUCENE-5722) Speed up MMapDirectory.seek()

["Robert Muir (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-5722?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Robert Muir updated LUCENE-5722:
--------------------------------

    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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