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https://issues.apache.org/jira/browse/LUCENE-2793?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12980551#action_12980551
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Shai Erera commented on LUCENE-2793:
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If we drop bufferSize, how will I be able to tell Lucene I'm willing to spare,
say, 1 MB buffer for this IndexInput/Output? Am I supposed to create my own
Directory and open II/IO, depending on the IOContext.Mode and decide on the
buffer size then?
If so, then I don't understand how this would work (think that's what Jason is
asking) - if I impl MyDirectory (extending Directory? FSDirectory?) which is
probably going to be a wrapper Directory, what II/IO impl should I invoke? I'll
need to extend BufferedIndexInput/Output, impl its abstract methods, just for
delegating to the wrapped Directory's II/IO?
If I misunderstood the intentions, I'd appreciate if you can clarify them. But
if not, I think IOContext should include a bufferSize hint. If the Directory
does not intend to do anything special for 'merging', then it can take
bufferSize into account. If however it's a Linux Directory that wants to set
the O_DIRECT, then it can ignore bufferSize. But I think it's a useful hint.
> Directory createOutput and openInput should take an IOContext
> -------------------------------------------------------------
>
> Key: LUCENE-2793
> URL: https://issues.apache.org/jira/browse/LUCENE-2793
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Store
> Reporter: Michael McCandless
> Attachments: LUCENE-2793.patch
>
>
> Today for merging we pass down a larger readBufferSize than for searching
> because we get better performance.
> I think we should generalize this to a class (IOContext), which would hold
> the buffer size, but then could hold other flags like DIRECT (bypass OS's
> buffer cache), SEQUENTIAL, etc.
> Then, we can make the DirectIOLinuxDirectory fully usable because we would
> only use DIRECT/SEQUENTIAL during merging.
> This will require fixing how IW pools readers, so that a reader opened for
> merging is not then used for searching, and vice/versa. Really, it's only
> all the open file handles that need to be different -- we could in theory
> share del docs, norms, etc, if that were somehow possible.
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