Re: [PERFORM] Number of characters in column preventing index usage

my_db=# create index tab_idx1 on tab(ID);                                                               

CREATE INDEX

my_db=# explain (analyze, buffers) select count(*) from tab where ID = '01625cfa-2bf8-45cf' ;                  

                                                              QUERY PLAN                                                               

---------------------------------------------------------------------------------------------------------------------------------------

 Aggregate  (cost=8.29..8.30 rows=1 width=0) (actual time=0.048..0.048 rows=1 loops=1)

   Buffers: shared read=2

   ->  Index Only Scan using tab_idx1 on tab  (cost=0.27..8.29 rows=1 width=0) (actual time=0.043..0.043 rows=0 loops=1)

         Index Cond: (ID = '01625cfa-2bf8-45cf'::text)

   ->  Seq Scan on tab  (cost=0.00..14.79 rows=5 width=0) (actual time=0.031..0.108 rows=5 loops=1)

         Filter: ((ID)::text = '01625cfa-2bf8-45cf-bf4c-aa5f3c6fa8ea'::text)

         Rows Removed by Filter: 218

         Buffers: shared hit=12

 Planning time: 0.122 ms

 Execution time: 0.180 ms

(8 rows)