PostgreSQL 10 High Performance - Third Edition

Lookup with an inefficient index

Is this new index worth being created? Consider a simple query that uses it to filter out based on the value:

EXPLAIN ANALYZE SELECT count(*) FROM t WHERE v=1;
QUERY PLAN
----------
Aggregate  (cost=756.55..756.56 rows=1 width=0) (actual time=31.962..31.963 rows=1 loops=1)
       ->  Bitmap Heap Scan on t  (cost=165.01..731.79 rows=9903 width=0) (actual time=1.821..18.010 rows=10054 loops=1)
             Recheck Cond: (v = 1)
             ->  Bitmap Index Scan on i  (cost=0.00..162.53 rows=9903 width=0) (actual time=1.721..1.721 rows=10054 loops=1)
                   Index Cond: (v = 1)
     Total runtime: 32.019 ms
    
      
    
    relname        | t
    seq_scan       | 1
    seq_tup_read   | 100000
    idx_scan       | 1
    idx_tup_fetch  | 10054
    heap_blks_read | 0
    heap_blks_hit  | 886
    idx_blks_read  | 25
    idx_blks_hit ...