Simple index lookups

If you use the primary key on the table, which was built using an index, it's possible to retrieve a row using that index quite quickly. This uses what's unsurprisingly called an index scan:

EXPLAIN ANALYZE SELECT count(*) FROM t WHERE k=1000;
QUERY PLAN                                                   
----------
Aggregate  (cost=8.28..8.29 rows=1 width=0) (actual time=0.034..0.036 rows=1 loops=1)
   ->  Index Scan using t_pkey on t  (cost=0.00..8.28 rows=1 width=0) (actual time=0.020..0.023 rows=1 loops=1)
         Index Cond: (k = 1000)
 Total runtime: 0.104 ms

seq_scan       | 0
seq_tup_read   | 0
idx_scan       | 1
idx_tup_fetch  | 1
heap_blks_read | 0
heap_blks_hit  | 1
idx_blks_read  | 0
idx_blks_hit   | 3

The second part here demonstrates what comes out of the pg_stat_reset/table_stats combination used around each of the statements in the preceding example as shown and used in the provided source code example.

This demonstrates the first...