[LUCENE-3201] improved compound file handling

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 4.0-ALPHA
• Lucene Fields: New
• Assignee: Simon Willnauer
• Reporter: Robert Muir
• Created: 13/Jun/11 23:57
• Updated: 28/Aug/22 12:49
• Resolved: 07/Oct/11 21:57

Description

Currently CompoundFileReader could use some improvements, i see the following problems

• its CSIndexInput extends bufferedindexinput, which is stupid for directories like mmap.
• it seeks on every readInternal
• its not possible for a directory to override or improve the handling of compound files.

for example: it seems if you were impl'ing this thing from scratch, you would just wrap the II directly (not extend BufferedIndexInput,
and add compound file offset X to seek() calls, and override length(). But of course, then you couldnt throw read past EOF always when you should,
as a user could read into the next file and be left unaware.

however, some directories could handle this better. for example MMapDirectory could return an indexinput that simply mmaps the 'slice' of the CFS file.
its underlying bytebuffer etc naturally does bounds checks already etc, so it wouldnt need to be buffered, not even needing to add any offsets to seek(),
as its position would just work.

So I think we should try to refactor this so that a Directory can customize how compound files are handled, the simplest
case for the least code change would be to add this to Directory.java:

  public Directory openCompoundInput(String filename) {
    return new CompoundFileReader(this, filename);
  }

Because most code depends upon the fact compound files are implemented as a Directory and transparent. at least then a subclass could override...
but the 'recursion' is a little ugly... we could still label it expert+internal+experimental or whatever.

Issue Links

• is part of: LUCENE-3218 Make CFS appendable