I did this earlier with an asynchronous threaded dataflow package I
wrote on top of elephant and it worked great. For the internal
problem that Alex outlines, it just shouldn't happen and I know how to
work around it. However, it would be good to have a general extension
allowing users to rollback non-db side effects on an abort.
Perhaps this could be a simple extension to the with-transaction
syntax? :on-abort sym|expr :on-commit sym|expr. Lambda expressions
would be compiled, symbols could refer to external functions much like
we handle keys on indexed-btrees. It would be nice to have a more
automated way of catching side effects though, but I think it's
impractical.
(Actually my little process components package allows you to define
and use a set of lisp variables visible to a body expression. The
package rewrote the body expression so that all side effected lisp
variables were cached and only saved on a commit - function calls
outside the body had to be handled explicitly though).
Anyone want to bite? It's a great little addition to Elephant and
shouldn't be too much work, at least once you understand all the
subtleties of the transaction macros and methods. I can help if you
get stuck.
Henrik, want to add a ticket if no one decides to do this in the near
term?
Ian
On Mar 11, 2008, at 10:52 AM, Henrik Hjelte wrote:
On Tue, Mar 11, 2008 at 11:18 AM, Alex Mizrahi
<[EMAIL PROTECTED]> wrote:
find-inverted-index does two things: creates DB object representing
index
and caches it.
then transaction is aborted -- all DB changes are effectively wiped.
but we still have references to DB object in %index-cache, and
accessing
it's slots produces errors:
A quick idea:
Can't elephant keep a list of lambda forms to be executed at commit
and perhaps a list of lambda forms to be executed at abort. Then
instead of directly caching it, you can make a lambda form that does
the caching, and push it to the list of commit actions. This will
defer execution of it to a safer time.
/Henrik
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