Re: [PATCH] Log crashed backend's query (activity string)

On Wed, Sep 7, 2011 at 5:24 PM, Alvaro Herrera
<alvherre@commandprompt.com> wrote:
> Excerpts from Marti Raudsepp's message of mié sep 07 18:09:32 -0300 2011:
>> On Wed, Sep 7, 2011 at 22:42, Alvaro Herrera <alvherre@commandprompt.com> wrote:
>> > A mishandled encoding conversion could be problematic, so that needs to
>> > be carefully considered (perhaps just shut off unconditionally).
>>
>> Are you referring to log file encoding or something else? The log file
>> is already potentially mixed-encoding, as different databases may have
>> different encodings and backends just dump bytes to it in their
>> current encoding.
>
> I am referring to the fact that whatever the backend puts in shared
> memory is going to be in its encoding setting, which may not necessarily
> match the postmaster's.  And if it doesn't, the postmaster might try to
> convert it using settings not valid for the string, possibly leading to
> crashes.
>
> I remember we had bugs whereby an encoding conversion would fail,
> leading to elog trying to report this problem, but this attempt would
> also incur a conversion step, failing recursively until elog's stack got
> full.  I'm not saying this is impossible to solve, just something to
> keep in mind.

Can we do something like: pass through ASCII characters unchanged, and
output anything with the high-bit set as \x<hexdigit><hexdigit>?  That
might be garbled in some cases, but the goal here is not perfection.
We're just trying to give the admin (or PostgreSQL-guru-for-hire) a
clue where to start looking for the problem.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company