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From DM Smith <>
Subject Re: Back Compatibility
Date Thu, 24 Jan 2008 18:44:32 GMT
This is now a hijacked thread. It is very interesting, but it may be 
hard to find again. Wouldn't it be better to record this thread 
differently, perhaps opening a Jira issue to add XA to Lucene?

-- DM

Doron Cohen wrote:
> On Jan 24, 2008 6:55 PM, robert engels <> wrote:
>> Thanks, you are correct, but I am not sure it covers the complete case.
>> Change it a bit to be:
>> A opens reader.
>> B opens reader.
>> A performs query decides a new document is needed
>> B performs query decides a new document is needed
>> B gets writer, adds document, closes
>> A gets writer, adds document, closes
>> There needs to be a way to manually serialize these operations. I
>> assume I should just do this:
>> A gets writer
>> B gets writer - can't so blocked
>> A opens reader
>> A performs query decides a new document is needed
>> A adds document
>> A closes reader
>> A closes writer
>> B now gets writer
>> B opens reader
>> B performs query sees a new document is not needed
>> B closes reader
>> B closes writer
>> Previously, with the read locks, I did not think you could open the
>> reader after you had the write lock.
>> Am I correct here?
> If  I understand you correctly then yes and no :-)
> "Yes" in the sense that this would work and achieve the
> required serialization, and "no" in that you could always open
> readers whether there was an open writer or not.
> The current locking logic with readers is that opening a reader does
> not require acquiring any lock. Only when attempting to use the reader
> for a write operation (e.g. delete) the reader becomes a writer, and
> for that it (1) acquires a write lock and (2) verifies that the
> index was not modified by any writer since the reader was
> first opened (or else it throws that stale exception).
> Prior to lockless-commit there were two lock types - write-lock and
> commit-lock. The commit-lock was used only briefly - during file opening
> during reader-opening, to guarantee that no writer modifies the files that
> the
> reader is reading (especially the segments file). Lockles-commits got rid
> of the commit lock (mainly by changing to never modify a file once it was
> written.) Write locks are still in use, but only for writers, as described
> above.
> (Mike feel free to correct me here...)

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