Re: optimizer not optimizing

Albert Vernon Smith wrote:
> I am in process of migrating from Pg 7.4.5 to 8.0.3. I have the same
> data loaded in to the two. However, when I do a query on my 8.0.3
> installation, I am not getting a very well optimized query. (All the
> memory settings are equivalent.)
>

Did you analyze on 8.0.3?

Sincerely,

Joshua D. Drake

> On 8.0.3, I get the following query plan:
>
> dbsnp_b125=# explain select * from b125_snpcontigloc_34_3 h join
> b125_contiginfo_34_3 c on c.ctg_id=h.ctg_id and c.contig_label=
> 'reference' join b125_snpmapinfo_34_3 m on m.snp_id=h.snp_id and
> m.assembly = 'reference' limit 50;
> QUERY PLAN
> ------------------------------------------------------------------------
> ---------------------------------------------------------------
> Limit (cost=13.17..23330.15 rows=50 width=1324)
> -> Nested Loop (cost=13.17..63181113458.28 rows=135483020 width=1324)
> Join Filter: ("outer".snp_id = "inner".snp_id)
> -> Index Scan using i_assembly_snpmapinfo_34 on
> b125_snpmapinfo_34_3 m (cost=0.00..391516.14 rows=113292 width=204)
> Index Cond: ((assembly)::text = 'reference'::text)
> -> Hash Join (cost=13.17..554703.83 rows=239175 width=1120)
> Hash Cond: ("outer".ctg_id = "inner".ctg_id)
> -> Seq Scan on b125_snpcontigloc_34_3 h
> (cost=0.00..472573.94 rows=15944994 width=676)
> -> Hash (cost=13.16..13.16 rows=3 width=444)
> -> Index Scan using i_contiginfo_contig_label_125
> on b125_contiginfo_34_3 c (cost=0.00..13.16 rows=3 width=444)
> Index Cond: ((contig_label)::text =
> 'reference'::text)
> (11 rows)
>
>
> While on 7.4.3, I get:
>
> dbsnp_b125=# explain select * from b125_snpcontigloc_34_3 h join
> b125_contiginfo_34_3 c on c.ctg_id=h.ctg_id and c.contig_label=
> 'reference' join b125_snpmapinfo_34_3 m on m.snp_id=h.snp_id and
> m.assembly = 'reference' limit 50;
> QUERY PLAN
> ------------------------------------------------------------------------
> -------------------------------------------------------
> Limit (cost=0.00..318.79 rows=50 width=441)
> -> Nested Loop (cost=0.00..1019222.39 rows=159859 width=441)
> -> Nested Loop (cost=0.00..313911.04 rows=175220 width=359)
> -> Index Scan using i_b125_34_contig_label on
> b125_contiginfo_34_3 c (cost=0.00..6.75 rows=3 width=252)
> Index Cond: ((contig_label)::text =
> 'reference'::text)
> -> Index Scan using i_b125h_34_ctg_id on
> b125_snpcontigloc_34_3 h (cost=0.00..103904.68 rows=58407 width=107)
> Index Cond: ("outer".ctg_id = h.ctg_id)
> -> Index Scan using i_b125_map_34_snp_id on
> b125_snpmapinfo_34_3 m (cost=0.00..4.01 rows=1 width=82)
> Index Cond: (m.snp_id = "outer".snp_id)
> Filter: ((assembly)::text = 'reference'::text)
> (10 rows)
>
> What could be the reason for this behavior???
>
> (I posted something similar a little while back, but I've still not
> solved this issue.)
>
> Thanks,
> -albert
>
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