Adrien Grand created LUCENE-4512:
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Summary: Additional memory savings in
CompressingStoredFieldsIndex.MEMORY_CHUNK
Key: LUCENE-4512
URL: https://issues.apache.org/jira/browse/LUCENE-4512
Project: Lucene - Core
Issue Type: Improvement
Reporter: Adrien Grand
Assignee: Adrien Grand
Priority: Minor
Fix For: 4.1
Robert had a great idea to save memory with
{{CompressingStoredFieldsIndex.MEMORY_CHUNK}}: instead of storing the absolute
start pointers we could compute the mean number of bytes per chunk of documents
and only store the delta between the actual value and the expected value
(avgChunkBytes * chunkNumber).
Given that the list of start pointers is stricly increasing, the error is at
most maxStartPointer / 2 (and is very likely to be much lower) so we are
guaranteed to save memory. (The same principle could be applied to docBases.)
By applying this idea to every n(=1024?) chunks, we would even:
- make sure to never hit the worst case (same memory usage as if we stored the
absolute offsets)
- reduce memory usage at indexing time.
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