multithreading, rebuilds, and updating.

[Shawn Heisey <so...@elyograg.org>]

I am planning to make my build system run with a couple of threads 
whenever there is a need for a full index rebuild.  One thread will 
handle the normal update process - indexing new content, reinserting 
changed documents, and deletes.  The other thread will handle rebuilds 
at the same time.

I'm working on thread locks so the processes won't stomp on each other, 
but I've come across a question:

The rebuild process will take a few hours (running on all the build 
cores), but the update process will happen at least once every two 
minutes (running on the live cores).  If a commit is underway on the 
live core, what will happen if another process asks Solr to swap the 
live core and the build core?  Will it blow up in some way?  Should my 
synchronization prevent these two processes from happening at the same time?

Because I will have just swapped the core out of the way of active 
queries, I don't actually care about the commit, but I do care about 
whether an exception will be thrown and that the index on the core 
(which is now the build core) is intact and won't cause a future rebuild 
to fail.

Thanks,
Shawn