We¹re running PostgreSQL 8.1.4 on RHEL. I¹m 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" <[EMAIL PROTECTED]> 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
>
