Thank you for the incredibly helpful (and fast) replies Peter.
> Attached is its output when I run your test query. The issue here is
that skip scan thinks that there are 4 distinct skip array values that
it must use:
1. SK_BT_MINVAL
2. false
3. true
4. SK_ISNULL
This output in particular really helped it make sense to me.
> But if the column *was* nullable, adding IS NOT NULL would cut the
number of index searches by 1.
>
Nice idea. Once it sunk in, I realised I could try the explicit "AND
boolean_field IN (true, false)" and got it down to 2 index searches:
EXPLAIN (ANALYZE, BUFFERS, VERBOSE, SETTINGS)
SELECT boolean_field FROM example WHERE integer_field = 5432 AND
boolean_field IN (true, false);
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------
Index Only Scan using bool_int_idx on public.example (cost=0.29..8.79
rows=10 width=1) (actual time=0.060..0.077 rows=12.00 loops=1)
Output: boolean_field
Index Cond: ((example.boolean_field = ANY ('{t,f}'::boolean[])) AND
(example.integer_field = 5432))
Heap Fetches: 0
Index Searches: 2
Buffers: shared hit=5
Planning Time: 0.265 ms
Execution Time: 0.115 ms
Thanks again,
Michael
