We have two servers configured the same way running the same type of
processes that write/read to the database. Server 2 filled up pg_xlog and
crashed. When it came back we began to experience slow query performance.
I ran an ANALYZE against the tables involved in the query, but for some
reason the optimizer is still choosing a hash join instead of a nested loop
join, which is killing performance. The query on Server 1 runs in 14
seconds and the same query on Server 2 runs in 15 minutes:
Server 1
-> HashAggregate (cost=501922.84..501922.85
rows=1 width=532)
-> Nested Loop (cost=250961.41..501922.83
rows=1 width=532)
Join Filter: (("outer".host)::text =
("inner".host)::text)
-> HashAggregate
(cost=250961.40..250961.41 rows=1 width=26)
-> Index Scan using
mxl_fs_size_did_cre_idx on mxl_fs_size (cost=0.01..250961.40 rows=1
width=26)
Index Cond: ((created >=
(now() - '01:00:00'::interval)) AND (created <= now()))
-> Index Scan using
mxl_fs_size_did_cre_idx on mxl_fs_size lh (cost=0.01..250961.40 rows=1
width=42)
Index Cond: ((created >= (now()
- '01:00:00'::interval)) AND (created <= now()))
Server 2
-> HashAggregate (cost=1814101.48..1814129.36
rows=2230 width=532)
-> Hash Join (cost=906978.28..1814079.18
rows=2230 width=532)
Hash Cond: (("outer".host)::text =
("inner".host)::text)
-> Index Scan using
mxl_fs_size_did_cre_idx on mxl_fs_size lh (cost=0.01..906877.88 rows=40147
width=42)
Index Cond: ((created >= (now()
- '01:00:00'::interval)) AND (created <= now()))
-> Hash (cost=906978.27..906978.27
rows=1 width=516)
-> HashAggregate
(cost=906978.25..906978.26 rows=1 width=26)
-> Index Scan using
mxl_fs_size_did_cre_idx on mxl_fs_size (cost=0.01..906877.88 rows=40147
width=26)
Index Cond:
((created >= (now() - '01:00:00'::interval)) AND (created <= now()))
Besides ANALYZE, what else can I do / look at to figure out why the
optimizer is making the choices it is on Server 2, now causing slow
performance problems?
Thanks,
Keaton
