On Feb 27, 2006, at 12:03 AM, Shaun Cutts wrote:



From: Tom Dossis [mailto:[EMAIL PROTECTED]
Shaun Cutts wrote:
But with replication, this issue is taken care of. (Too bad
replication
isn't part of the core functionality....)

Maybe soon..
   http://hathawaymix.org/Software/PGStorage

Great!

Another potential issue on the scalability front I had forgotten about
earlier:

How do BTrees perform under lots of concurrent updates? (I know this is
a tricky one, as implementations can get pretty complex to deal with
this.)

You've got a lot of questions. :-) I only have time to be quick, and hope that it is somewhat helpful. In that vein:

Pretty well. It has custom code to try to resolve conflicts. They are designed to handle it pretty well. That said, even with the special resolution code, catalogs (heavy BTree users) are often hotspots for conflicts, and sometimes get special treatment to serialize updates.

I note that
http://www.zope.org/Wikis/ZODB/FrontPage/guide/ node6.html#SECTION0006300
00000000000000

Says that "As with a Python dictionary or list, you should not mutate a
BTree-based data structure while iterating over it".

Does this apply only to thread-local modifications or to any
modification by anyone else?

thread-local (or more correctly, connection-local)

Ie, are BTrees "versioned" as the ZODB
is... if I'm iterating over a BTree in my process (in ZEO, say), and
another process modifies the BTree, does that sometimes show up in my
copy, or only after commit?

Only after commit.

Also, wrt "ConflictError" -- is the BTree considered one object, or are
the python objects (buckets, tree structure, ...) treated
separately?....

separately.

In general, are the BTrees just written "naively" on top of ZODB, or do
they interact in some special way with the storage?

Hm. They are certainly not "naive" of the ZODB; they authors have deep knowledge of the ZODB, and take advantage of ZODB hooks (such as the conflict resolution) and behavior.

Gary
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