Adrien Grand created LUCENE-9996:
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Summary: 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
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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