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https://issues.apache.org/jira/browse/LUCENE-9996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17418068#comment-17418068
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Adrien Grand commented on LUCENE-9996:
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I had not paid attention, but the nightly benchmarks for NYC Taxis noticed the
improvement from this issue as we could hold 9% more documents per MB of RAM
buffer in the sparse case
(http://people.apache.org/~mikemccand/lucenebench/sparseResults.html#index_docs_per_mb_ram).
> Can we improve DWPT's initial memory footprint?
> -----------------------------------------------
>
> Key: LUCENE-9996
> URL: https://issues.apache.org/jira/browse/LUCENE-9996
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Priority: Minor
> Fix For: 8.10
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> Say you are indexing only keyword fields, that are both indexed and have doc
> values. The first document that gets added to a DWPT will increase memory
> usage by about 80kB per field. This is due mostly to:
> - the {{BytesRefHash}} for the inverted index, which allocates a 32kB page
> - the {{BytesRefHash}} for the doc values terms dict, which allocates
> another 32kB page
> - the {{SortedDocValuesWriter#pending}} buffer that allocates a long[1024]:
> 8kB
> So if you have 10 actively indexing indices that have 100 fields each and 24
> indexing threads, this gives a total of 10*100*24*80kB = 1.8GB. If you
> happened to give less than 1.8GB for your indexing buffers overall, Lucene
> will likely do very small flushes that have only a few documents, which
> in-turn will make indexing rather slow.
> Could we improve DWPT so that it more progressively reserves memory as more
> documents get added?
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