[jira] [Created] (LUCENE-5646) stored fields bulk merging doesn't quite work right

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

Robert Muir created LUCENE-5646:
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             Summary: stored fields bulk merging doesn't quite work right
                 Key: LUCENE-5646
                 URL: https://issues.apache.org/jira/browse/LUCENE-5646
             Project: Lucene - Core
          Issue Type: Bug
            Reporter: Robert Muir
             Fix For: 4.9, 5.0


from doing some profiling of merging:

CompressingStoredFieldsWriter has 3 codepaths (as i see it):
1. optimized bulk copy (no deletions in chunk). In this case compressed data is copied over.
2. semi-optimized copy: in this case its optimized for an existing storedfieldswriter, and it decompresses and recompresses doc-at-a-time around any deleted docs in the chunk.
3. ordinary merging

In my dataset, i only see #2 happening, never #1. The logic for determining if we can do #1 seems to be:
{code}
onChunkBoundary && chunkSmallEnough && chunkLargeEnough && noDeletions
{code}

I think the logic for "chunkLargeEnough" is out of sync with the MAX_DOCS_PER_CHUNK limit? e.g. instead of:
{code}
startOffsets[it.chunkDocs - 1] + it.lengths[it.chunkDocs - 1] >= chunkSize // chunk is large enough
{code}

it should be something like:
{code}
(it.chunkDocs >= MAX_DOCUMENTS_PER_CHUNK || startOffsets[it.chunkDocs - 1] + it.lengths[it.chunkDocs - 1] >= chunkSize) // chunk is large enough
{code}

But this only works "at first" then falls out of sync in my tests. Once this happens, it never reverts back to #1 algorithm and sticks with #2. So its still not quite right.

Maybe [~jpountz] knows off the top of his head...



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