[LUCENE-5722] Speed up MMapDirectory.seek()

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.9, 6.0
• Component/s: core/store
• Lucene Fields: New
• Assignee: Uwe Schindler
• Reporter: Robert Muir
• Created: 31/May/14 06:15
• Updated: 28/Aug/22 14:08
• Resolved: 02/Jun/14 17:45

Description

For traditional lucene access which is mostly sequential, occasional advance(), I think this method gets drowned out in noise.

But for access like docvalues, its important. Unfortunately seek() is complex today because of mapping multiple buffers.

However, the very common case is that only one map is used for a given clone or slice.

When there is the possibility to use only a single mapped buffer, we should instead take advantage of ByteBuffer.slice(), which will adjust the internal mmap address and remove the offset calculation. furthermore we don't need the shift/mask or even the negative check, as they are then all handled with the ByteBuffer api: seek is a one-liner (with try/catch of course to convert exceptions).

This makes docvalues access 20% faster, I havent tested conjunctions or anyhting like that.