Re: [HACKERS] Optional message to user when terminating/cancelling backend

From: Daniel Gustafsson <daniel(at)yesql(dot)se>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Onder Kalaci <onder(at)citusdata(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Optional message to user when terminating/cancelling backend
Date: 2018-08-12 22:53:00
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> On 12 Aug 2018, at 11:01, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On August 12, 2018 12:17:59 AM GMT+02:00, Daniel Gustafsson <daniel(at)yesql(dot)se> wrote:
>>> On 6 Aug 2018, at 09:47, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>>> Has there been any consideration to encodings?
>> Thats a good point, no =/
>>> What happens if the message contains non-ASCII characters, and the
>> sending backend is connected to database that uses a different encoding
>> than the backend being signaled?
>> In the current state of the patch, instead of the message you get:
>> FATAL: character with byte sequence 0xe3 0x82 0xbd in encoding "UTF8"
>> has
>> no equivalent in encoding “ISO_8859_5"
>> Thats clearly not good enough, but I’m not entirely sure what would be
>> the best
>> way forward. Restrict messages to only be in SQL_ASCII? Store the
>> encoding of
>> the message and check the encoding of the receiving backend before
>> issuing it
>> for a valid conversion, falling back to no message in case there is
>> none?
>> Neither seems terribly appealing, do you have any better suggestions?
> Restricting to ASCII seems reasonable.

It’s quite restrictive, but it’s the safe option. I’ve hacked this into the
updated patch, but kept the backend_feedback() function using pg_mbstrlen() at
least for now since it seems the safe option should this be relaxed at some
point. Also added a small test by copying text from a ja.po file in the tree.

> But note that sqlascii isn't that (it's essentially just arbitrary null terminated data). Easier to relax later.

Yeah, my fingers and brain were not in sync during typing, I meant to say ASCII
there. I blame a lack of coffee.

cheers ./daniel

Attachment Content-Type Size
0001-Refactor-backend-signalling-code-v14.patch application/octet-stream 14.5 KB
0002-Support-optional-message-in-backend-cancel-terminate-v14.patch application/octet-stream 23.9 KB

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