[Seaside] ImageSegments as persistence

Avi Bryant avi at dabbledb.com
Mon Feb 19 20:59:07 UTC 2007

On 2/19/07, Sebastian Sastre <ssastre at seaswork.com> wrote:

>     Avi did you have any progress on that primitive that you want for array
> allocation to disk?

No.  I'm still interested in it if anyone has time.

>     I understood is file based and not atomical (transactional) and that it
> is like a piece of the image in another file.

It's certainly atomic in that there is a single primitive that builds
the segment.  But you'll need to do a lot of work yourself to get the
ACID properties you might want.

>     How much can one rely on them? any experience in production
> applications?

Once a segment is successfully built, I've never had any trouble
loading one into a new image (and Dabble DB has produced god knows how
many hundreds of thousands of image segments by this point).  The
problems are in building them - you have to be *very* careful not to
have any outpointers, and the allocation of the buffer to build the
segment can cause low-memory conditions more often than I'd like
(hence the desire for the disk-based version).

>     I think, that if reliable, it is an interesting option for seaside
> applications that do not require transactions.

If you understand and can carefully manage them, they certainly are.
But they're hardly an "out of the box" persistence solution.


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