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Posted to issues@lucene.apache.org by "Robert Muir (Jira)" <ji...@apache.org> on 2022/03/02 12:40:00 UTC
[jira] [Resolved] (LUCENE-10449) Performance regression due to decompressBlock method introduced with compression on binary doc values
[ https://issues.apache.org/jira/browse/LUCENE-10449?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Robert Muir resolved LUCENE-10449.
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Resolution: Not A Problem
Problem here is that user isn't using binary docvalues, they are using some other type
> Performance regression due to decompressBlock method introduced with compression on binary doc values
> ------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-10449
> URL: https://issues.apache.org/jira/browse/LUCENE-10449
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/codecs
> Affects Versions: 9.0
> Reporter: Renaud Delbru
> Priority: Major
> Attachments: lucene-8.11-no-compression.png, lucene-9.png
>
>
> LUCENE-9211 introduced a compression mechanism for binary doc values, which was then removed at a later stage in LUCENE-9843 as it was impacting performance on some workload.
> However, LUCENE-9843 didn't revert the code as it was prior to that. Instead of reading the block directly from the {{IndexInput}} as in [1], the {{decompressBlock()}} call [2] is kept which is decompressing a non-compress block (from our understanding). The {{decompressBlock}} method deleguates to {{LZ4.decompress }}and it looks like this is adding a significant overhead (e.g., {{{}readByte{}}}).
> This has quite an impact on our workloads which heavily uses doc values. It may lead to perf regression from 2x up to 5x. See samples below.
>
> {code:java}
> ❯ times_tasks Elasticsearch 7.10.2 (Lucene 8.7) - no binary compression
> name type time_min time_max time_p50 time_p90
> 7.10.2-22.6-SNAPSHOT.json total 42 90 45 66
> 7.10.2-22.6-SNAPSHOT.json SearchJoinRequest1 14 32 15 18
> 7.10.2-22.6-SNAPSHOT.json SearchTaskBroadcastRequest2 23 53 27 43
> ❯ times_tasks Elasticsearch 7.17.1 (Lucene 8.11) - with binary compression
> name type time_min time_max time_p50 time_p90
> 7.17.0-27.1-SNAPSHOT.json total 253 327 285 310
> 7.17.0-27.1-SNAPSHOT.json SearchJoinRequest1 121 154 142 152
> 7.17.0-27.1-SNAPSHOT.json SearchTaskBroadcastRequest2 122 173 140 152
> ❯ times_tasks Elasticsearch 7.17.1 (Lucene 8.11) - lucene_default codec is used to bypass the binary compression
> name type time_min time_max time_p50 time_p90
> 7.17.0-27.1-SNAPSHOT.json.2 total 48 96 63 75
> 7.17.0-27.1-SNAPSHOT.json.2 SearchJoinRequest1 19 44 25 31
> 7.17.0-27.1-SNAPSHOT.json.2 SearchTaskBroadcastRequest2 23 42 29 37
> ❯ times_tasks Elasticsearch 8.0 (Lucene 9.0) - no binary compression
> name type time_min time_max time_p50 time_p90
> 8.0.0-28.0-SNAPSHOT.json total 260 327 287 313
> 8.0.0-28.0-SNAPSHOT.json SearchJoinRequest1 122 168 148 158
> 8.0.0-28.0-SNAPSHOT.json SearchTaskBroadcastRequest2 123 165 139 155{code}
> We can clearly see that in Lucene 9.0, even after the removal of the binary doc values compression, the performance didn't improve. Profiling the execution indicates that the bottleneck is the {{{}LZ4.decompress{}}}. We have attached two screenshots of a flamegraph.
> The CPU time of the {{TermsDict.next}} method with Lucene 8.11 with no compression is around 2 seconds, while the CPU time of the same method in Lucene 9.0 is 12 seconds. This was measured on a small benchmark reading a fixed number of times a binary doc values field. Each document is created with a single binary value that represents a UUID.
>
> [1] [https://github.com/apache/lucene-solr/blob/releases/lucene-solr/8.11.0/lucene/core/src/java/org/apache/lucene/codecs/lucene80/Lucene80DocValuesProducer.java#L1159]
> [2] [https://github.com/apache/lucene/commit/a7a02519f0a5652110a186f4909347ac3349092d#diff-ab443662a6310fda675a4bd6d01fabf3a38c4c825ec2acef8f9a34af79f0b252R1022]
>
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