[jira] [Created] (LUCENE-10616) Moving to dictionaries has made stored fields slower at skipping

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

Adrien Grand created LUCENE-10616:
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             Summary: Moving to dictionaries has made stored fields slower at skipping
                 Key: LUCENE-10616
                 URL: https://issues.apache.org/jira/browse/LUCENE-10616
             Project: Lucene - Core
          Issue Type: Bug
            Reporter: Adrien Grand


[~ywelsch] has been digging into a regression of stored fields retrieval that is caused by LUCENE-9486.

Say your documents have two stored fields, one that is 100B and is stored first, and the other one that is 100kB, and you are only interested in the first one. While the idea behind blocks of stored fields is to store multiple documents in the same block to leverage redundancy across documents, sometimes documents are larger than the block size. As soon as documents are larger than 2x the block size, our stored fields format splits such large documents into multiple blocks, so that you wouldn't need to decompress everything only to retrieve a couple small fields.

Before LUCENE-9486, BEST_SPEED had a block size of 16kB, so only retrieving the first field value would only need to decompress 16kB of data. With the move to preset dictionaries in LUCENE-9486 and then LUCENE-9917, we now have blocks of 80kB, so stored fields would now need to decompress 80kB of data, 5x more than before.

With dictionaries, our blocks are now split into 10 sub blocks. We happen to eagerly decompress all sub blocks that intersect with the stored document, which is why we would decompress 80kB of data, but this is an implementation detail. It should be possible to decompress these sub blocks lazily so that we would only decompress those that intersect with one of the field values that the user is interested in retrieving?



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