improved compound file handling
-------------------------------
Key: LUCENE-3201
URL: https://issues.apache.org/jira/browse/LUCENE-3201
Project: Lucene - Java
Issue Type: Improvement
Reporter: Robert Muir
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:
{code}
public Directory openCompoundInput(String filename) {
return new CompoundFileReader(this, filename);
}
{code}
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.
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