plope - Wherefore CouchDB for ZODB Users - The Diigo Meta page

• 10 Dec 08
  

  Olifante *

  "All in all, CouchDB is a neat piece of software. If I ever have to build an application that needs to store data that needs to be accessible from programs written in langauges other than Python across HTTP and I don't need to use a relational database, it seems like a great solution."

  python zodb couchdb database comparison strengths overview

  • I didn't understand why
    folks were excited about CouchDB given that a good number of its
    features (append-only storage and "schemaless design" in particular)
    have been present in ZODB for a
    little under ten years now. Even more in particular, I was really
    baffled as to why Python developers were excited about such a system
    given the availability of ZODB.
  • I think I understand a bit better now. ZODB and CouchDB are quite
    similar in a lot of respects, but CouchDB beats ZODB on a narrow set
    of goals that seem to be becoming more important
  • 10 more annotations...
  • • the documented way to
      talk to CouchDB is over HTTP, and because you send it JSON primitives
      containing data structures, it can be used from just about any program
      written in just about any language. And given that most folks are not
      accustomed to being able to access any database without dark-magic C
      bindings that speak strange connection-oriented TCP protocols (or the
      equivalent embedded usually-crashy C bindings and awkward APIs), this
      is probably a novelty for many users.
    • CouchDB has a built-in
      indexing and querying facility, in the form of
      Views.
      This is something that ZODB does not share. Instead, ZODB relies on
      applications that are built on top of it to provide indexing
      capabilities. Moreover, creating indexes in applications that use
      ZODB is historically a static kind of thing that the application
      developer does "up front", or at least as a "software release" sort of
      thing. In CouchDB, creating an index is not really an exceptional
      sort of event. You tell the server, over HTTP, to create the index by
      PUT-ing a view. The first time any view is queried, CouchDB does the
      indexing. The following times the view is queried, it uses the index
      you've created via the view to return the results faster. No
      application that I know of written on top of ZODB allows you to do
      such a thing so casually.
    • All in all, CouchDB is a neat piece of software. If I ever have to
      build an application that needs to store data that needs to be
      accessible from programs written in langauges other than Python across
      HTTP and I don't need to use a relational database, it seems like a
      great solution.
    • ZODB is probably still a better choice if your application is 100%
      Python and you want arbitrary application database write logic to be
      bounded within a single transaction.
    • if you need to store large amounts of
      data (like arbitrary numbers of multimegabyte or multigigabyte files),
      ZODB is also probably a better choice, as it has blobs built in, and
      the blobs don't need to be base64 encoded in memory as "attachments"
    • if you need to
      store data structures that cannot be represented as JSON (like complex
      object instances), ZODB really can't be beat.
    • CouchDB no longer requires encoding
      binary data in base64. Attachments for documents (that work just like email
      attachments) have their own REST API since this summer where you can
      send the raw binary data to create and retrieve documents. So storing loads
      of data is no longer a bad idea.
    • You can think of a ZODB database
      as a place to hang a graph of arbitrary Python objects that becomes
      persistent. It's sort of an "uber-pickle"
    • You can use packages like
      repoze.catalog to do indexing
      and querying of object data that is inserted into the graph. You can
      use packages like
      repoze.folder to hold
      large collections of objects.
    • The "Zope" in ZODB is a
      "brand-only" name; it does not require Zope; it can be used in any
      Python application.

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