public inbox for [email protected]  

help / color / mirror / Atom feed

From: Heikki Linnakangas <[email protected]>
To: Jelte Fennema-Nio <[email protected]>
To: PostgreSQL Hackers <[email protected]>
To: Alvaro Herrera <[email protected]>
To: Jacob Champion <[email protected]>
Subject: Re: Don't use the deprecated and insecure PQcancel in our frontend tools anymore
Date: Mon, 16 Mar 2026 11:57:47 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>

On 15/03/2026 17:09, Jelte Fennema-Nio wrote:
> On Fri Mar 6, 2026 at 8:51 PM CET, Heikki Linnakangas wrote:
>> I worry how this behaves if establishing the cancel connection gets 
>> stuck for a long time. Because of a network hiccup, for example. 
>> That's also not a new problem though; it's perhaps even worse today, 
>> if the signal handler gets stuck for a long time, trying to establish 
>> the connection. Still, would be good to do some testing with a bad 
>> network.
> 
> After thinking on this again, I thought of a much easier solution to
> this problem than the direction I was exploring in my previous response
> to this: We can have SetCancelConn() and ResetCancelConn() wait for any 
> pending
> cancel to complete before letting them replace/remove the cancelConn.
> 
> That way even in case of a bad network, we know that an already
> in-flight cancel request will never cancel a query from a next
> SetCancelConn() call. It does mean that you cannot submit a new query
> before we've received a response to the in-flight cancel request (either
> because the hiccup is reselved or because TCP timeouts report a
> failure). That's the current behaviour too with running PQcancel in the
> signal handler, and I also think that's the behaviour that makes the
> most sense.

+1. With a little extra effort, the cancellation can be made abortable 
too, so that you don't need to wait for the TCP timeout. I.e when 
ResetCancelConn() is called, the cancellation thread can immediately 
call PQcancelReset().

One a different topic, is there any guarantee on which thread will 
receive the SIGINT? It matters because psql's cancel callback sometimes 
calls longjmp(), which assumes that the signal handler is executed in 
the main thread.

- Heikki

view thread (11+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected], [email protected], [email protected]
  Subject: Re: Don't use the deprecated and insecure PQcancel in our frontend tools anymore
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox