Re: Cluster name in ps output

Hi,

On 2014-05-05 10:00:34 +0000, Thomas Munro wrote:
> When running more than one cluster I often find myself looking at
> the output of 'iotop' or other tools wondering which
> cluster's "wal receiver process" or "checkpointer process" etc
> I'm seeing.

I wonder about that pretty regularly. To the point that I've a hacky
version of this locally. So +1 for me for the idea in general.

> If cluster_name is not set, it defaults to the empty string and
> the ps output is unchanged.  If it's set to 'foox' the ps output
> includes that string in square brackets:
>
>   postgres: [foox] checkpointer process
>   postgres: [foox] writer process
>   postgres: [foox] wal writer process
>   postgres: [foox] autovacuum launcher process
>   postgres: [foox] stats collector process
>   postgres: [foox] munro foodb [local] idle

"postgres: [foox] ..." should rather be "postgres[foox]: ..." imo ;)

I guess the question is where this should be available as well. At the
very least I'd want to reference it in log_line_prefix as well?

> +     if (*cluster_name == '\0')
> +     {
> +             snprintf(ps_buffer, ps_buffer_size,
> +                              PROGRAM_NAME_PREFIX "%s %s %s ",
> +                              username, dbname, host_info);
> +     }
> +     else
> +     {
> +             snprintf(ps_buffer, ps_buffer_size,
> +                              PROGRAM_NAME_PREFIX "[%s] %s %s %s ",
> +                              cluster_name, username, dbname, host_info);
> +     }
> +
>       ps_buffer_cur_len = ps_buffer_fixed_size = strlen(ps_buffer);

Aren't you potentially dereferencing a NULL pointer here?