Re: Feature improvement: can we add queryId for pg_catalog.pg_stat_activity view?

On Thu, Apr  8, 2021 at 08:47:48AM +0800, Julien Rouhaud wrote:
> On Wed, Apr 07, 2021 at 07:38:35PM -0400, Bruce Momjian wrote:
> > On Wed, Apr  7, 2021 at 07:01:25PM -0400, Tom Lane wrote:
> > > Bruce Momjian <bruce@momjian.us> writes:
> > > > Uh, I think your patch missed a few things.  First, you use "%zd"
> > > > (size_t) for the printf string, but calls to pgstat_get_my_queryid() in
> > > > src/backend/utils/error/elog.c used "%ld".  Which is correct?  I see
> > > > pgstat_get_my_queryid() as returning uint64, but I didn't think a uint64
> > > > fits in a BIGINT SQL column.
> > > 
> > > Neither is correct.  Project standard these days for printing [u]int64
> > > is to write "%lld" or "%llu", with an explicit (long long) cast on
> > > the printf argument.
> > 
> > Yep, got it.  The attached patch fixes all the calls to use %lld, and
> > adds casts.  In implementing cvslog, I noticed that internally we pass
> > the hash as uint64, but output as int64, which I think is a requirement
> > for how pg_stat_statements has output it, and the use of bigint.  Is
> > that OK?
> 
> Indeed, this is due to how we expose the value in SQL.  The original discussion
> is at
> https://www.postgresql.org/message-id/CAH2-WzkueMfAmY3onoXLi+g67SJoKY65Cg9Z1QOhSyhCEU8w3g@mail.gmail.com.
> As far as I know this is OK, as we want to show consistent values everywhere.

OK, yes, I do remember the discussion.  I was wondering if there should
be a C comment about this anywhere.

> > I am also confused about the inconsistency of calling the GUC
> > compute_query_id (with underscore), but pg_stat_activity.queryid.  If we
> > make it pg_stat_activity.query_id, it doesn't match most of the other
> > *id columsns in the table, leader_pid, usesysid, backend_xid.  Is that
> > OK?I know I suggested pg_stat_activity.query_id, but maybe I was wrong.
> 
> Mmm, most of the columns in pg_stat_activity do have a "_", so using query_id
> would make more sense.

OK, let me work on a patch to change that part.

> @@ -2967,6 +2967,10 @@ write_csvlog(ErrorData *edata)
> 
>      appendStringInfoChar(&buf, '\n');
> 
> +    /* query id */
> +    appendStringInfo(&buf, "%lld", (long long) pgstat_get_my_queryid());
> +    appendStringInfoChar(&buf, ',');
> +
> 
>      /* If in the syslogger process, try to write messages direct to file */
>      if (MyBackendType == B_LOGGER)
>          write_syslogger_file(buf.data, buf.len, LOG_DESTINATION_CSVLOG);
>
> Unless I'm missing something this will output the query id in the next log
> line?  The new code should be added before the newline is output, and the comma
> should also be output before the queryid.

Yes, correct, updated patch attached.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.