Details
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Type:
Improvement
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Status: Resolved
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Priority:
Major
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: 7.0
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Component/s: None
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Labels:None
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Lucene Fields:New
Description
Today, when users delete documents or apply doc values updates, IndexWriter buffers them up into frozen packets and then eventually uses a single thread (BufferedUpdatesStream.applyDeletesAndUpdates) to resolve delete/update terms to docids. This thread also holds IW's monitor lock, so it also blocks refresh, merges starting/finishing, commits, etc.
We have heavily optimized this part of Lucene over time, e.g. LUCENE-6161, LUCENE-2897, LUCENE-2680, LUCENE-3342, but still, it's a single thread so it can't use multiple CPU cores commonly available now.
This doesn't affect append-only usage, but for update-heavy users (me!) this can be a big bottleneck, and causes long stop-the-world hangs during indexing.
I have an initial exploratory patch to make these lookups concurrent, without holding IW's lock, so that when a new packet of deletes is pushed, which happens when we flush a new segment, we immediately use that same indexing thread to and resolve the deletions.
This is analogous to when we made segment flushing concurrent (LUCENE-3023), just for deletes and DV updates as well.
