Re: Why so much time difference with a same query/plan?

Does the order of columns in the index matter since
more than 50% customer_id = 158?

I think it does not in Oracle.

Will the performance be better if I change index
xxx_idx to ("domain", customer_id, created)?

I will test myself when possible.

Thanks,

--- Litao Wu <litaowu(at)yahoo(dot)com> wrote:

> Merry Xmas!
>
> I have a query. It sometimes runs OK and sometimes
> horrible. Here is result from explain analyze:
>
> explain analyze
> SELECT module, sum(c1) + sum(c2) + sum(c3) +
> sum(c4)
> + sum(c5) AS "count"
> FROM xxx
> WHERE created >= ('now'::timestamptz - '1
> day'::interval) AND customer_id='158'
> AND domain='xyz.com'
> GROUP BY module;
>
> There is an index:
> Indexes: xxx_idx btree (customer_id, created,
> "domain")
>
> Table are regularlly "vacuum full" and reindex and
> it has 3 million rows.
>
>
>
> QUERY PLAN
>
>
>
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> Aggregate (cost=139.53..141.65 rows=12 width=30)
> (actual time=17623.65..17623.65 rows=0 loops=1)
> -> Group (cost=139.53..140.14 rows=121
> width=30)
> (actual time=17623.64..17623.64 rows=0 loops=1)
> -> Sort (cost=139.53..139.83 rows=121
> width=30) (actual time=17623.63..17623.63 rows=0
> loops=1)
> Sort Key: module
> -> Index Scan using xxx_idx on xxx
> (cost=0.00..135.33 rows=121 width=30) (actual
> time=17622.95..17622.95 rows=0 loops=1)
> Index Cond: ((customer_id =
> 158)
> AND (created >= '2004-12-02
> 11:26:22.596656-05'::timestamp with time zone) AND
> ("domain" = 'xyz.com'::character varying))
> Total runtime: 17624.05 msec
> (7 rows)
>
>
> QUERY PLAN
>
>
>
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> Aggregate (cost=142.05..144.21 rows=12 width=30)
> (actual time=1314931.09..1314931.09 rows=0 loops=1)
> -> Group (cost=142.05..142.66 rows=124
> width=30)
> (actual time=1314931.08..1314931.08 rows=0 loops=1)
> -> Sort (cost=142.05..142.36 rows=124
> width=30) (actual time=1314931.08..1314931.08 rows=0
> loops=1)
> Sort Key: module
> -> Index Scan using xxx_idx on xxx
> (cost=0.00..137.74 rows=124 width=30) (actual
> time=1314930.72..1314930.72 rows=0 loops=1)
> Index Cond: ((customer_id =
> 158)
> AND (created >= '2004-12-01
> 15:21:51.785526-05'::timestamp with time zone) AND
> ("domain" = 'xyz.com'::character varying))
> Total runtime: 1314933.16 msec
> (7 rows)
>
> What can I try?
>
> Thanks,
>
>
>
>
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