[jira] [Created] (LUCENE-9996) Can we improve DWPT's initial memory footprint?

["Adrien Grand (Jira)" <ji...@apache.org>]

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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