[Zope] Questions on ZODB BTrees versus bsddb BTrees

[Terry Jones]

Hi Chris

>>>>> "Chris" == Chris Withers <chris at simplistix.co.uk> writes: You may
Chris> have more joy with these questions on the zodb-dev at zope.org mailing
Chris> list...

Thanks, I've re-sent. Thanks for the other comments & pointers too.

Regards
Terry.


>> - ZODB BTrees do not allow you to set up secondary keys (a la bsddb).
Chris> Dunno what that means. I think you're just use two BTrees for this...

[Sorry if the following is off-topic for the list. It's presumably good for
the archives, and, I suppose, is the end of the thread.]

>From the Berkeley DB docs:

    Usually you find database records by means of the record's key.
    However, the key that you use for your record will not always contain
    the information required to provide you with rapid access to the data
    that you want to retrieve. For example, suppose your database contains
    records related to users. The key might be a string that is some unique
    identifier for the person, such as a user ID. Each record's data,
    however, would likely contain a complex object containing details about
    people such as names, addresses, phone numbers, and so forth.  While
    your application may frequently want to query a person by user ID (that
    is, by the information stored in the key), it may also on occasion want
    to location people by, say, their name.

    Rather than iterate through all of the records in your database,
    examining each in turn for a given person's name, you create indexes
    based on names and then just search that index for the name that you
    want.  You can do this using secondary databases. In DB, the database
    that contains your data is called a primary database. A database that
    provides an alternative set of keys to access that data is called a
    secondary database. In a secondary database, the keys are your
    alternative (or secondary) index, and the data corresponds to a primary
    record's key.