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Date: Tue, 26 Nov 2002 11:14:49 -0500
From: jeremy@alum.mit.edu (Jeremy Hylton)
To: skip@pobox.com
Subject: Re: [Spambayes] Guidance re pickles versus DB for Outlook
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>>>>> "SM" == Skip Montanaro <skip@pobox.com> writes:

  Jeremy> Put another way, I'd be interested to hear why you don't
  Jeremy> want to use ZODB.

  SM> Disclaimer: I'm not saying I don't want to use ZODB.  I'm
  SM> offering some reasons why it might not be everyone's obvious
  SM> choice.

But you're not saying you do want to use ZODB, so you're still part of
the problem <wink>.

  SM> For most of us who have *any* experience with ZODB it's probably
  SM> all indirect via Zope, so there are probably some inaccurate
  SM> perceptions about it.  These thoughts that have come to my mind
  SM> at one time or another:

  SM> * How could a database from a company (Zope) whose sole business
  SM>       is not databases be more reliable than a database from
  SM>       organizations whose sole raison d'etre is databases
  SM>       (Sleepycat, Postgres, MySQL, ...)?

I don't think I could argue that ZODB is more reliable that
BerkeleyDB.  It's true that we have fewer database experts and expend
fewer resources working on database reliability.  On the other hand,
Barry is nearly finished with a BerkeleyDB-based storage for ZODB.

ZODB is an object persistence tool that uses a database behind it.
You can use our FileStorage or you can use someone else's database,
although BerkeleyDB is the best we can offer at the moment.  (It would
be really cool to do a Postgres storage...)

  SM> * Dealing with Zope's monolithic system is frustrating to people
  SM>       (like me) who are used to having files reside in
  SM>       filesystems.  Some of that frustration probably carries
  SM>       over to ZODB, though it's almost certainly not ZODB's
  SM>       problem.


This sounds like a Zope complaint that doesn't have anything to do
with ZODB, but maybe I misunderstand you.  You don't have to store
your code in the database, although that will be mostly possible in
ZODB4.

Seriously, ZODB stores object pickles in a database.  The storage
layer is free to manage those pickles however it likes.  FileStorage
uses a single file.  Toby Dickenson's DirectoryStorage represents each
pickle as a separate file.

  SM> * It seems to grow without bound, else why do I need to pack my
  SM>       Data.fs file every now and then?

It grows without bound unless you pack it.  Why is that a problem? 
BerkeleyDB log files grow without bound, too.  Databases require some
tending.  One possibility with FileStorage is to add an explicit
pack() call to update training operation.  We'd need to think
carefully about the performance impact.

  SM> Also, there is the issue of availability.  While it's just an
  SM> extra install, its use requires more than the usual Python
  SM> install.  Having it in the core distribution would provide
  SM> stronger assurances that it runs wherever Python runs (e.g.,
  SM> does it run on MacOS 8 or 9, both of which I believe Jack still
  SM> supports with his Mac installer?).

I think we'd want a spambayes installer that packaged up spambayes,
python, and zodb.

Jeremy


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