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From Michael McCandless <luc...@mikemccandless.com>
Subject Re: indexWriter.addIndexes, Disk space, and open files
Date Tue, 08 Jun 2010 16:37:46 GMT
On Mon, Jun 7, 2010 at 7:19 AM, Regan Heath
<regan.heath@bridgeheadsoftware.com> wrote:
>
>>> That's pretty much exactly what I suspected was happening.  I've had the
> same
>>> problem myself on another occasion... out of interest is there any way to
>>> force the file closed without flushing?
>>
>>No, IndexOutput has no such method.  We could consider adding one...
>
> That sounds useful in general.
>
> In our case what we actually want is to abort the merge and delete all the
> new files created.

This is in fact what Lucene will do, if the disk full is hit during merge.

If the disk full is hit during flush(), Lucene discards those docs
that were the RAM buffer.

> But then, our usage may be slightly unusual in that we
> merge an existing 'master' index and a number of 'temporary' indices into a
> new master index.  On success we delete the old master and rename the new
> master into it's place.
>
> We're doing disk space checks prior to merge, based on the docs here:
> http://lucene.apache.org/java/2_3_2/api/org/apache/lucene/index/IndexWriter.html#optimize()
>
> but I disabled these to test this out of disk space case, as it is possible
> something else could use up the required space during the merge.
>
>>> From memory I tried everything I
>>> could think of at the time but couldn't manage it.  Best I could do was
>>> catch and swallow the expected exception from close and carry on.
>>
>>I think that's the best to do w/ today's API; but, you should save the
>>first IOE you hit, then force close the remaining files, then throw
>>that IOE.
>
> When you say 'force' close do you just mean wrapping the close calls in
> try/catch(IOException) where the catch block is empty (swallows the
> exception)?  Or is there a specific call to force a file closed?

The former.  There is no method.

>>> So, the only option for us is to upgrade the version of lucene we're
>>> using
>>> to the current trunk?  Is there no existing stable release version
>>> containing the fix?  If not, when do you estimate the next stable release
>>> with the fix will be available?
>>
>>I don't think any release of Lucene will have fixed all of these
>>cases, yet.  Patches welcome :)
>
> I would if I had the time, or sufficient understanding of the existing code,
> sadly I've only looked at it for 5  mins. :(

Start small then iterate... add that static method somewhere and call
it from a place or two :)

>>Actually, the best fix is something Earwin created but is not yet
>>committed (nor in a patch yet, I think), which adds a nice API for
>>closing multiple IndexOutputs safely.  Earwin, maybe you could pull
>>out just this part of your patch and open a separate issue?  Then we
>>can fix all places in Lucene that need to close multiple IndexOutputs
>>to use this API.
>
> That sounds great.. I'm not sure if something like this is useful to you..
>
> public class Safe
> {
>    /**
>     * Safely closes any object that implements closeable
>     *
>     * @param     closeable The object to close
>     */
>    public static void close(Closeable closeable)
>    {
>        try
>        {
>            closeable.close();
>        }
>        catch(Exception e)
>        {
>            // ignore
>        }
>        finally
>        {
>            closeable = null;
>        }
>    }
> }
>
> We use this in catch and finally blocks where we do not want to raise an
> exception.

That looks great!  I think Earwin's version took multiple Closeables
and closed them all, which would be useful.

We'd also want a way to close N closeables, but, if any exception is
hit on closing any of them, throw that exception, but still force the
remaining ones closed.

Mike

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