Warn when actual rows are significantly different than estimated rows in an EXPLAIN ANALYZE in postgres

WARN-on-bad-estimate

postgres=# create table t(a integer); create index t_idx on t(a);                                                                                                      
CREATE TABLE
CREATE INDEX
postgres=# insert into t select g from generate_series(1,10) g;                                                                                                        
INSERT 0 10
postgres=# explain analyze select * from t where a > 8;                                                                                                                
        				QUERY PLAN
-------------------------------------------------------------------------------------------
 Seq Scan on t  (cost=0.00..1.12 rows=2 width=4) (actual time=0.017..0.019 rows=2 loops=1)
   Filter: (a > 8)
   Rows Removed by Filter: 8
 Total runtime: 0.055 ms
(4 rows)

postgres=# insert into t select g from generate_series(8, 80000) g; explain analyze select * from t where a > 8;                                                       
INSERT 0 79993
WARNING:  Actual row counts differ significantly from estimated row counts
                                                      QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------
 Index Only Scan using t_idx on t  (cost=0.00..296.11 rows=787 width=4) (actual time=0.020..17.971 rows=79994 loops=1)
   Index Cond: (a > 8)
   Heap Fetches: 79994
 Total runtime: 20.878 ms
(4 rows)

postgres=# analyze t;                                                                                                                                                  
ANALYZE
postgres=# explain analyze select * from t where a > 8;                                                                                                                
                                              QUERY PLAN
-------------------------------------------------------------------------------------------------------
 Seq Scan on t  (cost=0.00..1354.04 rows=79996 width=4) (actual time=0.038..18.047 rows=79994 loops=1)
   Filter: (a > 8)
   Rows Removed by Filter: 9
 Total runtime: 23.147 ms
(4 rows)

postgres=#