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From Chris Hostetter <hossman_luc...@fucit.org>
Subject Re: [jira] Resolved: (LUCENE-1044) Behavior on hard power shutdown
Date Sun, 04 Nov 2007 00:35:51 GMT

: This is simple not true. See FileDescriptor.sync().
: 
: There are several options, but normally it is used so that when close
: completes, all data must be on disk. This is a much slower way to write data.
: It is very common in database systems when committing the log file.

Ok.  I'll certainly take your word for it ... i've been trusting the docs 
for [File]OutputStream.flush()...

>> If the intended destination of this stream is an abstraction provided 
>> by the underlying operating system, for example a file, then flushing 
>> the stream guarantees only that bytes previously written to the stream 
>> are passed to the operating system for writing; it does not guarantee 
>> that they are actually written to a physical device such as a disk drive.

I haven't looked at the internals of FileOutputStream or FileDescriptor on 
any particular platforms to see how exactly they work, but if dealing with 
the FD directly and using FD.sync() the magic bullet then I'd love to see 
a patch that uses it in FSDirectory.

I assume the SyncFailedException it throws is rare?  If it is always 
thrown when using things like NFS that may be a show stopper for using 
sync() in Lucene ... many people have jumped through a lot of hoops this 
past year to get Lucene working on NFS; I'd hate to see all that work go 
out the window in an effort to make Lucene ACID.  (I suspect there are 
more users interested in using Lucene on NFS then on using it as a 
transactional data store)

>> Throws:
>>    SyncFailedException - Thrown when the buffers cannot be flushed, or 
>> because the system cannot guarantee that all the buffers have been 
>> synchronized with physical media.

-Hoss


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