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From Otis Gospodnetic <otis_gospodne...@yahoo.com>
Subject RE: existing or not existing
Date Thu, 06 Dec 2001 15:24:47 GMT
Yes, I would use this, especially the IndexReader methods that you
suggested.

Otis

--- Doug Cutting <DCutting@grandcentral.com> wrote:
> > From: Otis Gospodnetic [mailto:otis_gospodnetic@yahoo.com]
> > 
> > You could try looking for a segments file in the index directory.
> > If it exists, the index exists, else it does not.
> > 
> > Is there a better way?
> 
> I think that's currently the best way.  But it's not great, because
> it
> requires applications to know something about the internal structure
> of the
> index.
> 
> Going forward, I'm hesitant to change the semantics of the 'create'
> flag.
> I'm also hesitant to add another flag or constructor method.
> 
> Perhaps the addition of the following IndexReader methods would
> suffice:
> 
>   /** Returns true iff an index exists in the named directory. */
>   public static boolean indexExists(String directory);
>   public static boolean indexExists(File directory);
>   public static boolean indexExists(Directory directory);
> 
> These are analogous to the 'lastModified' methods. Internally these
> would
> just check for the existence of the segments file.
> 
> Does that sound like a good plan?
> 
> Another place that currently requires application knowledge of index
> structure is failure recovery.  Currently if an indexing application
> crashes
> it may leave .lock files in the directory which must be removed
> before the
> index can be altered again.  Perhaps this can be resolved similarly
> by
> adding methods like:
> 
>   /** Returns true iff the index in the named directory is currently
> locked.*/
>   public static boolean isLocked(Directory directory);
> 
>   /** Forcibly unlocks the index in the named directory. 
>    * Caution: this should only be used by failure recovery code,
>    * when it is known that no other process or thread is in fact
>    * currently accessing this index.
>    */
>   public static void unlock(Directory directory);
> 
> We could also have String and File versions for convenience.
> 
> Would folks use something like this?  If so, more fodder for the TODO
> list!
> 
> Doug
> 
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