Re: Logging conflicted queries on deadlocks

ITAGAKI Takahiro wrote:

> I wrote a small patch to log conflicted queries.
> With my patch, deadlock message will change as following:
>
> | ERROR: deadlock detected
> | DETAIL: Process 3468 waits for ShareLock on transaction 451; blocked by process 4068.
> | STATEMENT: UPDATE test SET i = i WHERE i = 1; <- ***conflicted query***
> | Process 4068 waits for ShareLock on transaction 450; blocked by process 3468.
> | STATEMENT: UPDATE test SET i = i WHERE i = 2;

Cute.

> There are some open issues. One of the issues is that the killed query is
> logged by log_min_error_statement, but conflicted query is logged in DETAIL.
> Killed query is logged only on server but conflicted queries are
> sent to both server and client. In addition, if log_min_error_statement
> is less than ERROR level, only the conflicted queries are logged.
> -- it's inconsistent and unsymmetric.

Perhaps it could be shown in CONTEXT, like so:

| ERROR: deadlock detected
| DETAIL: Process 3468 waits for ShareLock on transaction 451; blocked by process 4068.
| Process 4068 waits for ShareLock on transaction 450; blocked by process 3468.
| STATEMENT: UPDATE test SET i = i WHERE i = 2;
| CONTEXT: process 3468: UPDATE test SET i = i WHERE i = 1;

I think it's useful to show the PID of each statement, for the case
where there are more than two processes deadlocked.

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.