slow sort

Hi there,

here is another one from the "why is my query so slow?" category. First post, so please bare with me.

The query (which takes around 6 seconds) is this:

SET work_mem TO '256MB';//else sort spills to disk

SELECT
et.subject,
COALESCE (createperson.vorname || ' ', '') || createperson.nachname AS "Sender/Empfänger",
to_char(es.sentonat, 'DD.MM.YY') AS "versendet am",
es.sentonat AS orderbydate,
COUNT (ct.*),
COALESCE (C . NAME, 'keine Angabe') :: TEXT AS "für Kunde",
COUNT (ct.datetimesentonat) :: TEXT || ' von ' || COUNT (ct.*) :: TEXT || ' versendet',
1 AS LEVEL,
TRUE AS hassubs,
FALSE AS opensubs,
'emailsendings:' || es. ID :: TEXT AS model_id,
NULL :: TEXT AS parent_model_id,
es. ID
FROM
emailtemplates et
JOIN emailsendings es ON et. ID = es.emailtemplate_id
LEFT JOIN companies C ON C . ID = es.customers_id
LEFT JOIN personen createperson ON createperson. ID = et.personen_create_id
LEFT JOIN contacts ct ON ct.emailsendings_id = es. ID WHERE f_record_visible_to_currentuser(et.*::coretable) = true
GROUP BY
1,
2,
3,
4,
6,
8,
9,
10,
11,
12,
13
ORDER BY
es.sentonat desc

Explain analyze:

GroupAggregate (cost=35202.88..45530.77 rows=118033 width=142) (actual time=5119.783..5810.680 rows=898 loops=1)
-> Sort (cost=35202.88..35497.96 rows=118033 width=142) (actual time=5119.356..5200.457 rows=352744 loops=1)
Sort Key: es.sentonat, et.subject, ((COALESCE((createperson.vorname || ' '::text), ''::text) || createperson.nachname)), (to_char(es.sentonat, 'DD.MM.YY'::text)), ((COALESCE(c.name, 'keine Angabe'::character varying))::text), (1), (true), (false), (('emailsendings:'::text || (es.id)::text)), (NULL::text), es.id
Sort Method: quicksort Memory: 198999kB
-> Nested Loop Left Join (cost=0.00..25259.29 rows=118033 width=142) (actual time=1.146..1896.382 rows=352744 loops=1)
-> Nested Loop Left Join (cost=0.00..2783.16 rows=302 width=102) (actual time=1.127..32.577 rows=898 loops=1)
-> Merge Join (cost=0.00..2120.06 rows=302 width=86) (actual time=1.125..30.940 rows=898 loops=1)
Merge Cond: (et.id = es.emailtemplate_id)
-> Nested Loop Left Join (cost=0.00..2224.95 rows=277 width=74) (actual time=1.109..27.484 rows=830 loops=1)
-> Index Scan using emailtemplates_pkey on emailtemplates et (cost=0.00..460.71 rows=277 width=63) (actual time=1.097..20.541 rows=830 loops=1)
Filter: f_record_visible_to_currentuser((et.*)::coretable)
-> Index Scan using personen_pkey on personen createperson (cost=0.00..6.36 rows=1 width=19) (actual time=0.006..0.006 rows=1 loops=830)
Index Cond: (createperson.id = et.personen_create_id)
-> Index Scan using fki_emailsendings_emailtemplate_id_fkey on emailsendings es (cost=0.00..49.83 rows=905 width=20) (actual time=0.011..1.360 rows=898 loops=1)
-> Index Scan using firmen_pkey on companies c (cost=0.00..2.18 rows=1 width=24) (actual time=0.001..0.001 rows=0 loops=898)
Index Cond: (c.id = es.customers_id)
-> Index Scan using fki_contacts_emailsendings_id_fkey on contacts ct (cost=0.00..61.55 rows=561 width=44) (actual time=0.019..0.738 rows=393 loops=898)
Index Cond: (ct.emailsendings_id = es.id)
Total runtime: 5865.886 ms

I do have an index on es.sentonat. The sentonat-values are all unique, so I don't think I need indexes on all the fields I sort by. But then again, my understanding of this might be entirely wrong.

Depeszs' explain (http://explain.depesz.com/s/69O) tells me this:

node type count sum of times % of query
GroupAggregate 1 610.223 ms 10.5 %
Index Scan 5 690.503 ms 11.9 %
Merge Join 1 2.096 ms 0.0 %
Nested Loop Left Join 3 1203.783 ms 20.7 %
Sort 1 3304.075 ms 56.9 %

, so the sort appears to be the problem. Any pointers would be highly appreciated.

Maximilian Tyrtania
http://www.contactking.de