[ZODB-Dev] OID length

[Jim Fulton]

Tim Peters wrote:
> [Florent Guillaume]
> 
>>I know this has been raised several times in the past, but I'm not sure
>>of all the details...
> 
> 
> You should believe whatever Jim tells you ;-)

Hey, what's the wink for?

> 
>>What layer of ZODB, if any, has a restriction that OIDs be 8-byte
>>strings. Is it the persistence module? Or just FileStorage?
> 
> 
> FileStorage uses oids that are exactly 8-byte strings.  The implementation
> of the FileStorage index (built on the special-purpose fsBTree type) relies
> on that heavily.
> 
> The UML model for ZODB 3 claims that "In ZODB 3, object identifiers are
> 8-byte strings"

That's out of date.

 > generally, but at least Shane Hathaway's APE got away with
> using (at least for some time) much longer strings.  I'm not sure where the
> code actually relies on "stringness", though -- looks like most of it would
> work provided oids were totally ordered, hashable, immutable, and
> pickle-able (so that oids can be used as keys in Python dicts and in
> BTrees).

I thought this was settled in:

   http://mail.zope.org/pipermail/zodb-dev/2005-March/008593.html

which also mentions the requirement that oids must have len > 0. :)

We should really document this in IPersistent.

>>and would anyone be interested in seeing it removed.
>>
>>I'm asking because I'm planning a pretty complex storage layer, which
>>would benefit from more complex OIDs (for instance bigger strings, or
>>tuples of (str, int)).
 >
> An oid is a low-level implementation thingie,  and IMO that's probably not
> the right place to put complexity.  If you don't expect to have more than
> 2**N objects, an oid that requires more than N bits is in some sense
> extravagant ;-).  In any case, you should be able to use "bigger strings"
> now without changing anything.

Yup.

Jim

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