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List:       postgresql-sql
Subject:    Re: [SQL] plan not correct?
From:       Adrian Klaver <adrian.klaver () aklaver ! com>
Date:       2016-03-21 16:04:31
Message-ID: 56F01B8F.5030506 () aklaver ! com
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On 03/21/2016 08:29 AM, Bert wrote:
> That is easy to check.
> 
> Let's do the same test again:
> # select count(1) from dlp.st_itemseat;
> count
> -------
> 12
> (1 row)
> 
> # select count(1) from loaddlp.st_itemseat_insert;
> count
> -------
> 87      --> of which 12 are already in the dlp.st_itemseat table
> (1 row)
> 
> # explain analyze <upsert query>*
> QUERY PLAN
> -----------------------------------------------------------------------------------------------------------------------------------------------------------------
>  Insert on st_itemseat  (cost=55.47..69.97 rows=150 width=228) (actual
> time=2.345..2.345 rows=0 loops=1)
> CTE upsert
> ->  Update on st_itemseat et  (cost=17.50..55.42 rows=2 width=240)
> (actual time=0.493..0.545 rows=12 loops=1)
> ->  Hash Join  (cost=17.50..55.42 rows=2 width=240) (actual
> time=0.303..0.318 rows=12 loops=1)
> Hash Cond: ((et.tick_server_id =
> st_itemseat_insert_1.tick_server_id) AND (et.itemseat_id =
> st_itemseat_insert_1.itemseat_id))
> ->  Seq Scan on st_itemseat et  (cost=0.00..13.10
> rows=310 width=14) (actual time=0.025..0.028 rows=12 loops=1)
> ->  Hash  (cost=13.00..13.00 rows=300 width=234)
> (actual time=0.244..0.244 rows=87 loops=1)
> Buckets: 1024  Batches: 1  Memory Usage: 13kB
> ->  Seq Scan on st_itemseat_insert
> st_itemseat_insert_1  (cost=0.00..13.00 rows=300 width=234) (actual
> time=0.005..0.120 rows=87 loops=1)
> ->  Seq Scan on st_itemseat_insert  (cost=0.04..14.54 rows=150
> width=228) (actual time=0.637..0.726 rows=75 loops=1)
> Filter: (NOT (hashed SubPlan 2))
> Rows Removed by Filter: 12
> SubPlan 2
> ->  CTE Scan on upsert  (cost=0.00..0.04 rows=2 width=8)
> (actual time=0.498..0.561 rows=12 loops=1)
> Planning time: 1.122 ms
> Execution time: 2.682 ms
> 
> # <upsert query>*
> INSERT 0 0
> 
> # select count(1) from dlp.st_itemseat;
> count
> -------
> 87
> (1 row)
> 
> 
> * the upsert query can be found attached to the first mail, but the
> difference is that the 'where loadtabletime' is removed
> 
> As you can see the in the update part of the explain the 'rows' nr is
> 12. Which is what is expected.
> But the rows on the insert are again 0, while it should be 75.

They are seen, including the 12 rows that are filtered out for updating:

" ->  Seq Scan on st_itemseat_insert  (cost=0.04..14.54 rows=150 
width=228) (actual time=0.637..0.726 rows=75 loops=1)
          Filter: (NOT (hashed SubPlan 2))
          Rows Removed by Filter: 12
          SubPlan 2
"

I do not know why that value is not propagated up to 'Insert on 
st_itemseat ...'.

> 
> wkr,
> Bert
> 



-- 
Adrian Klaver
adrian.klaver@aklaver.com


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