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https://issues.apache.org/jira/browse/LUCENE-2316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12855736#action_12855736
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Michael McCandless commented on LUCENE-2316:
--------------------------------------------
I don't think Lucene relies on file length; we do use it for
diagnostics/logging (eg IW's infoStream).
Hmm I guess we do use it for merging purposes (LogByteSizeMergePolicy), where
we try to merge roughly similarly sized (by net size in bytes) segments.
I would rather not increase our reliance on it (eg LUCENE-2373 proposes to do
so) -- it's a piece of metadata that is sometimes (eg over NFS) less reliable
than file contents. The less we rely on from the filesystem the more
robust/portable Lucene will be...
Net/net I think we should keep the method, but restrict our use of it.
I do think we should move to throwing FNFE if the file does not exist... though
I think a break in back compat may be OK, here? (Vs do the new
method/deprecated/abstract approach).
> Define clear semantics for Directory.fileLength
> -----------------------------------------------
>
> Key: LUCENE-2316
> URL: https://issues.apache.org/jira/browse/LUCENE-2316
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Shai Erera
> Priority: Minor
> Fix For: 3.1
>
>
> On this thread:
> http://mail-archives.apache.org/mod_mbox/lucene-java-dev/201003.mbox/%[email protected]%3e
> it was mentioned that Directory's fileLength behavior is not consistent
> between Directory implementations if the given file name does not exist.
> FSDirectory returns a 0 length while RAMDirectory throws FNFE.
> The problem is that the semantics of fileLength() are not defined. As
> proposed in the thread, we'll define the following semantics:
> * Returns the length of the file denoted by <code>name</code> if the file
> exists. The return value may be anything between 0 and Long.MAX_VALUE.
> * Throws FileNotFoundException if the file does not exist. Note that you can
> call dir.fileExists(name) if you are not sure whether the file exists or not.
> For backwards we'll create a new method w/ clear semantics. Something like:
> {code}
> /**
> * @deprecated the method will become abstract when #fileLength(name) has
> been removed.
> */
> public long getFileLength(String name) throws IOException {
> long len = fileLength(name);
> if (len == 0 && !fileExists(name)) {
> throw new FileNotFoundException(name);
> }
> return len;
> }
> {code}
> The first line just calls the current impl. If it throws exception for a
> non-existing file, we're ok. The second line verifies whether a 0 length is
> for an existing file or not and throws an exception appropriately.
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