Re: compute_query_id and pg_stat_statements

At Thu, 13 May 2021 12:11:12 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> As the result, even if we take the DLL approach, still not need to
> split out the query-id provider part. By the following config:
> 
> > query_id_provider = 'pg_stat_statements'
> 
> the core can obtain the entrypoint of, say, "_PG_calculate_query_id"
> to call it. And it can be of another module.
> 
> It seems like the only problem doing that is we don't have a means to
> call per-process intializer for a preload libralies.

So this is a crude PoC of that.

pg_stat_statemnts defines its own query-id provider function in
pg_stat_statements which calls in-core DefaultJumbeQuery (end emits a
log line).

If server started with query_id_provider='auto' and pg_stat_statements
is not loaded, pg_stat_activity.query_id is null.

If query_id_provider='auto' and pg_stat_statements is loaded,
pg_stat_activity.query_id is filled in with a query id.

If query_id_provider='default' or 'pg_stat_statements' and
pg_stat_statements is not loaded, pg_stat_activity.query_id is filled
in with a query id.

If query_id_provider='none' and pg_stat_statements is loaded, it
complains as "query id provider is not available" and refuss to start.

If showing the variable, it shows the real provider name instead of
the setting in postgresql.conf.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center