[LUCENE-2816] MMapDirectory speedups

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.1, 4.0-ALPHA
• Component/s: core/store
• Lucene Fields: New, Patch Available
• Assignee: Robert Muir
• Reporter: Robert Muir
• Created: 17/Dec/10 08:34
• Updated: 26/Dec/10 15:04
• Resolved: 26/Dec/10 15:04

Description

MMapDirectory has some performance problems:

1. When the file is larger than Integer.MAX_VALUE, we use MultiMMapIndexInput,
   which does a lot of unnecessary bounds-checks for its buffer-switching etc.
   Instead, like MMapIndexInput, it should rely upon the contract of these operations
   in ByteBuffer (which will do a bounds check always and throw BufferUnderflowException).
   Our 'buffer' is so large (Integer.MAX_VALUE) that its rare this happens and doing
   our own bounds checks just slows things down.
2. the readInt()/readLong()/readShort() are slow and should just defer to ByteBuffer.readInt(), etc
   This isn't very important since we don't much use these, but I think there's no reason
   users (e.g. codec writers) should have to readBytes() + wrap as bytebuffer + get an
   IntBuffer view when readInt() can be almost as fast...