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> We still need to decide what to do with queue full situations in
> the proposed listen/notify implementation. I have a new version
> of the patch to allow for a variable payload size. However, the
> whole notification must fit into one page so the payload needs
> to be less than 8K.
That sounds fine to me, FWIW.
> I have also added the XID, so that we can write to the queue before
> committing to clog which allows for rollback if we encounter write
> errors (disk full for example). Especially the implications of this
> change make the patch a lot more complicated.
Can you elaborate on the use case for this?
> so it won't update its pointer for some time. With the current space we can
> acommodate at least 2147483647 notifications or more, depending on the
> payload length.
That's a whole lot of notifications. I doubt any program out there is using
anywhere near that number at the moment. In my applications, having a
few hundred notifications active at one time is "a lot" in my book. :)
> These are the solutions that I currently see:
>
> 1) drop new notifications if the queue is full (silently or with rollback)
I like this one best, but not with silence of course. While it's not the most
polite thing to do, this is for a super extreme edge case. I'd rather just
throw an exception if the queue is full rather than start messing with the
readers. It's a possible denial of service attack too, but so is the current
implementation in a way - at least I don't think apps would perform very
optimally with 2147483647 entries in the pg_listener table :)
If you need some real-world use cases involving payloads, let me know, I've
been waiting for this feature for some time and have it all mapped out.
- --
Greg Sabino Mullane greg@turnstep.com
PGP Key: 0x14964AC8 200911160902
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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