| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Shay Rojansky <roji(at)roji(dot)org> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Proposed change to make cancellations safe |
| Date: | 2016-04-25 16:34:25 |
| Message-ID: | 6530.1461602065@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Shay Rojansky <roji(at)roji(dot)org> writes:
>> Issuing bulk cancellations sounds like a bad plan.
> I'm not sure why, but at the very least it's a useful thing to have when
> batching several statements together and then wanting to cancel them all.
We really do need "cancel up to" semantics for reliable behavior.
Consider the case where the client has sent the query (or thinks it has)
but the server hasn't received it yet. If the cancel request can arrive
at the server before the query fully arrives, and we don't have "cancel
all messages up through N" semantics, the cancel will not do what the
client expects it to.
regards, tom lane
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