Re: approve VKPts5 unsubscribe pgsql - Mailing list pgsql-sql

Hi!

1. I have:
vladimir=> explain SELECT acc.ifs_account_id FROM
vladimir->      ifs_account acc,
vladimir->      ifs_tree_default def,
vladimir->      ifs_account_tree_data atd
vladimir-> WHERE
vladimir->     acc.ifs_status_id = 12
vladimir-> AND atd.ifs_tree_id IN(14,26)
vladimir-> AND def.ifs_tree_default_id IN(587,175)
vladimir-> AND atd.ifs_account_id = acc.ifs_account_id
vladimir-> AND atd.ifs_data_id = def.ifs_data_id;
NOTICE:  QUERY PLAN:

Nested Loop  (cost=0.00 rows=1 width=16) ->  Seq Scan on ifs_account acc  (cost=0.00 rows=0 width=4) ->  Seq Scan
(cost=757.02rows=1 width=12)
 
(**)        ->  ???  (cost=757.02 rows=1 width=12)             ->  Hash Join  (cost=757.02 rows=1 width=12)
     ->  Seq Scan on ifs_account_tree_data atd  (cost=751.76 rows=3 width=8
 
)                   ->  Hash  (cost=4.07 rows=3 width=4)                         ->  Index Scan using
xpkifs_tree_default,xpkifs_tree_default onifs_tree_default def  (cost=4.07 rows=3 width=4)
 

What mean "???" at (**).
There is no index? Or unknown method?

2. Seq Scan - Sequential Scan - this mean FULL TABLE SCAN (DATA SCAN)?

3. I try to play with indeces on this tables
3.1. Setting all btree indeces
explain SELECT acc.ifs_account_id FROM    ifs_account acc,     ifs_tree_default def,     ifs_account_tree_data atd
WHERE   acc.ifs_status_id = 12
AND atd.ifs_tree_id IN(14,26)
AND def.ifs_tree_default_id IN(587,175)
AND atd.ifs_account_id = acc.ifs_account_id
AND atd.ifs_data_id = def.ifs_data_id;

Nested Loop  (cost=0.00 rows=1 width=16) ->  Nested Loop  (cost=0.00 rows=1 width=12)       ->  Seq Scan on
ifs_tree_defaultdef  (cost=0.00 rows=0 width=4)       ->  Seq Scan on ifs_account_tree_data atd  (cost=0.00 rows=0
width=8)->  Seq Scan on ifs_account acc  (cost=0.00 rows=0 width=4)
 

Not optimal way I think

2. I've replace btree indexes on relation
AND atd.ifs_data_id = def.ifs_data_id;
with:
create index itd_hash_data_id on ifs_tree_default USING HASH (ifs_data_id);
create index iatd_hash_data_id on ifs_account_tree_data USING HASH (ifs_data_id);

PS: Can't replace on on ifs_account_id because of PRIMARY KEY (may be
direct Alternative Entry helps me, but is it right way to optimize?)

so:
Nested Loop  (cost=0.00 rows=1 width=16) ->  Seq Scan on ifs_account acc  (cost=0.00 rows=0 width=4) ->  Seq Scan
(cost=10.17rows=1 width=12)       ->  ???  (cost=10.17 rows=1 width=12)             ->  Nested Loop  (cost=10.17 rows=1
width=12)                  ->  Index Scan using xpkifs_tree_default, xpkifs_tree_default on ifs_tree_default def
(cost=4.07          ows=3 width=4)                   ->  Index Scan using xif588ifs_account_tree_data on
ifs_account_tree_d              ata atd  (cost=2.03 rows=3 width=8)
 

3. I've delete all indexes on
AND atd.ifs_data_id = def.ifs_data_id;

Then I've got:
Nested Loop  (cost=0.00 rows=1 width=16) ->  Seq Scan on ifs_account acc  (cost=0.00 rows=0 width=4) ->  Seq Scan
(cost=757.02rows=1 width=12)       ->  ???  (cost=757.02 rows=1 width=12)             ->  Hash Join  (cost=757.02
rows=1width=12)                   ->  Seq Scan on ifs_account_tree_data atd  (cost=751.76 rows=3 width=8
 
)                   ->  Hash  (cost=4.07 rows=3 width=4)                         ->  Index Scan using
xpkifs_tree_default,xpkifs_tree_default onifs_tree_default def  (cost=4.07 rows=3 width=4)
 

Hash Join appears. But there is no indexes, so "Table Scan" appears
(approximately 18000 rows in ifs_account_tree_data)? BAD!?!

So, where is the optimal way?
To make separate queries and use temporary tables to decrease JOINs?


Regards, Alexey V. Meledin
InterForge Developers Group, Saint-Petersburg
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