Re: explain hashAggregate

Good morning,

I try to understand how optimizer uses HashAggregate instead of GroupAggregate
and I want to know what is exactly this two functionnality (benefits
/inconvenients)

In my case, I've this explain plan.
-----------------------
Nested Loop (cost=2451676.23..2454714.73 rows=1001 width=34)
-> Subquery Scan "day" (cost=2451676.23..2451688.73 rows=1000 width=16)
-> Limit (cost=2451676.23..2451678.73 rows=1000 width=12)
-> Sort (cost=2451676.23..2451684.63 rows=3357 width=12)
Sort Key: sum(occurence)
-> HashAggregate (cost=2451471.24..2451479.63 rows=3357
width=12)
-> Index Scan using test_date on
queries_detail_statistics (cost=0.00..2449570.55 rows=380138 width=12)
Index Cond: ((date >= '2006-01-01'::date) AND
(date <= '2006-01-30'::date))
Filter: (((portal)::text = '1'::text) OR
((portal)::text = '2'::text))
-> Index Scan using query_string_pkey on query_string (cost=0.00..3.01
rows=1 width=34)
Index Cond: ("outer".query = query_string.id)
----------------------------
How to get necessary memory RAM for this explain plan ?

thanks a lot