关于BDB-Directory 的问答

问：

Is it possible to turn off directory locking with BDB?  How is the performance
compared to regular FSDirectory for queries?

答：

If you're thinking of using Berkeley DB as a the store behind the Lucene index
via the DbDirectory Directory implementation, here are a few things to keep in
mind:

   - always setUseCompoundFile(false)
     don't use compound lucene index files on top of Berkeley DB:
      . there is a bug that prevents this from working correctly
      . it makes no sense anyway since it duplicates what DbDirectory is
        already doing (all index files are stored in the same Berkeley DB file)
      . it slows things down

   - if you are using a transaction around all the index updates, you may want
     to consider doing all the index updates in a RAMDirectory first and then
     adding the RAMDirectory wholesale to the DbDirectory in that transaction.
     This makes indexing considerably faster (3 times for me) and does a LOT
     less thrashing around in Berkeley DB which can lead to a large number of
     transactional log files rapidly filling up your hard drive.

I'm not really sure if and how index merging works. For my use, having no
merging is good enough since I never update existing documents, but always
instead add a new version of them. The concept of version is tied to my
application and each transaction corresponds to a new version.