We’re running PostgreSQL 8.1.4 on RHEL. I’m running a vacuum analyze on the mxl_fs_size table to see if that shows anything.
-Keaton
On 12/4/07 10:50 PM, "Keaton Adams" <kadams@xxxxxxxxxxx> wrote:
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
