On 04/04/2009, at 7:25 PM, Sven Helmberger wrote:
Spring allows you to create application-wide singletons, one of
which
could be the jcouchdb Database object.
In order to keep the write serialization more or less transparent to
the application developer, I guess
1) I'd write an aspect on top of that bean, that would proxy the
update/delete related operations, adding the identity of object
operated on to an active object list (exact data structure might
vary).
2) Another aspect would handle the bulk insert method; it would
check
if any of the objects being inserted/updated are already in the
active
objects list, and if not, add all the inserted object ids to the
active object list before update, and removing them afterwards.
3) Operations (update/delete) that affect objects already in active
object list would simply throw an exception without even hitting
couchdb.
Then just serialize the access to that active object list. What do
you think?
You would still get conflict on update unless you serialise all
access and check the existing rev of all intended updates before
committing. I'm not sure the active list buys you much - you also
need to deal with replication updating the db.
I wonder if there's really a way to handle this in any transparent
way (with or without Spring/AOP).
To me it seems like a explicit working set you can add stuff to and
that you can finally commit would be most helpful. I'm not sure how
such a thing should work. You can sure add all kinds of documents to
the working set and use bulk update to commit it, but what do you do
when some of the documents conflict? Trying to restore the
conflicting documents' previous revision seems like the best bet,
but even that seems like it can't really work in all cases.
I'm going to bet that it's not possible, if for no other reason than
the lack of a low level interposition mechanism that covers updates
generated by replication.
Antony Blakey
--------------------------
CTO, Linkuistics Pty Ltd
Ph: 0438 840 787
Reflecting on W.H. Auden's contemplation of 'necessary murders' in the
Spanish Civil War, George Orwell wrote that such amorality was only
really possible, 'if you are the kind of person who is always
somewhere else when the trigger is pulled'.
-- John Birmingham, "Appeasing Jakarta"
