Re: Planning counters in pg_stat_statements (using pgss_store)

Thanks for the excellent extension. I want to add 5 more fields to satisfy
the
following requirements.

int subplan; /* No. of subplan in this query */
int subquery; /* No. of subquery */
int joincnt; /* How many relations are joined */
bool hasagg; /* if we have agg function in this query */
bool hasgroup; /* has group clause */

1. Usually I want to check total_exec_time / rows to see if the query is
missing
index, however aggregation/groupby case makes this rule doesn't work. so
hasagg/hasgroup should be a good rule to filter out these queries.

2. subplan is also a important clue to find out the query to turning. when
we
check the slow queries with pg_stat_statements, such information maybe
helpful as well.

3. As for subquery / joincnt, actually it is just helpful for optimizer
developer to understand the query character is running most, it doesn't
help
much for user.

The attached is a PoC, that is far from perfect since 1). It maintain a
per-backend global variable query_character which is only used in
pg_stat_statements extension. 2). The 5 fields is impossible to change no
matter how many times it runs, so it can't be treat as Counter in nature.
However I don't think the above 2 will cause big issues.

I added the columns to V1_8 rather than adding a new version. this can be
changed at final patch.

Any suggestions?

Best Regards
Andy Fan