Re: [HACKERS] Query cancel and OOB data

> Bruce Momjian wrote:
>
> > OK, thanks to Tom Lane's many patches, I have query cancel working on my
> > machine. However, it is not working with Unix domain sockets. I get:
> >
> > Cannot send cancel request:
> > PQrequestCancel() -- couldn't send OOB data: errno=45
> > Operation not supported
> >
> > This is under BSDI 3.1.
> >
> > Do Unix Domain sockets support OOB(out-of-band) data?
> >
>
> Unix domain sockets don't support OOB (Stevens, Unix Network Programming).

Yea, I found that too, late last night, Section 6.14, page 332.

I basically need some way to 'signal' the backend of a cancellation
request. Polling the socket is not an option because it would impose
too great a performance penalty. Maybe async-io on a read(), but that
is not going to be very portable.

I could pass the backend pid to the front end, and send a kill(SIG_URG)
to that pid on a cancel, but the frontend can be running as a different
user than the backend. Problem is, the only communcation channel is
that unix domain socket.

We basically need some way to get the attention of the backend,
hopefully via some signal.

Any ideas?

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