[LUCENE-3254] BitVector.isSparse is sometimes wrong

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.4, 4.0-ALPHA
• Component/s: core/other
• Lucene Fields: New
• Assignee: Michael McCandless
• Reporter: Michael McCandless
• Created: 28/Jun/11 13:47
• Updated: 28/Aug/22 12:51
• Resolved: 28/Jun/11 17:44

Description

In working on LUCENE-3246, I found a few problems with
BitVector.isSparse:

• Its math can overflow int, such that if there are enough deleted
  docs and maxDoc() is largish, isSparse may incorrectly return true

• It over-estimates the size of the sparse file, since when
  estimating number of bytes for the vInt dgaps it uses bits.length
  instead of bits.length divided by number of set bits (ie, the
  "average" gap between set bits)

This is relatively harmless (just affects performance / size of .del
file on disk, not correctness).