Partition pruning for Star Schema

Hi,

On 2017-12-02 13:56:51 -0700, legrand legrand wrote:

I have a typical star schema, having dimension tables "product", "calendar"
and "country" and a fact table "sales".
This fact table is partitionned by time (range by month) and country
(list).

You've posted nearly the same a few days ago:
http://archives.postgresql.org/message-id/1511986639005-0.post%40n3.nabble.com

Please don't just duplicate threads just because you've not received an
answer a few days ago. If you'd done additional research / provided more
context *and* linked to the last time you sent something it'd be
different.

Greetings,

Andres Freund

Sorry, I apologize.
I though (most) Hackers were not reading General list.

Regards
PAscal

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On Sun, Dec 3, 2017 at 5:56 AM, legrand legrand
<legrand_legrand@hotmail.com> wrote:

Hello,

I have a typical star schema, having dimension tables "product", "calendar"
and "country" and a fact table "sales".
This fact table is partitionned by time (range by month) and country (list).

Will query like:

select product.name, calendar.month, sum(sales.net_price)
from sales
inner join product on (product.id = sales.cust_id)
inner join country on (country.id = sales.country_id)
inner join calendar on (calendar.id = sales.calendar_id)
where
country.name = 'HERE'
and calendar.year = '2017'
group by product.name,calendar.month

be able to identify needed partitions ?

AFAIU partition pruning, it works only with the partition key columns.
So, if country.name and calendar.year are the partition keys partition
pruning would identify the needed partitions from those tables. But
planner doesn't know that calendar.year is somehow related to
calendar.id and then transfer that knowledge so that partitions of
sales can be identified.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

On 04/12/17 16:08, Ashutosh Bapat wrote:

On Sun, Dec 3, 2017 at 5:56 AM, legrand legrand
<legrand_legrand@hotmail.com> wrote:

Hello,

I have a typical star schema, having dimension tables "product", "calendar"
and "country" and a fact table "sales".
This fact table is partitionned by time (range by month) and country (list).

Will query like:

select product.name, calendar.month, sum(sales.net_price)
from sales
inner join product on (product.id = sales.cust_id)
inner join country on (country.id = sales.country_id)
inner join calendar on (calendar.id = sales.calendar_id)
where
country.name = 'HERE'
and calendar.year = '2017'
group by product.name,calendar.month

be able to identify needed partitions ?

AFAIU partition pruning, it works only with the partition key columns.
So, if country.name and calendar.year are the partition keys partition
pruning would identify the needed partitions from those tables. But
planner doesn't know that calendar.year is somehow related to
calendar.id and then transfer that knowledge so that partitions of
sales can be identified.

If you can get your code to perform a star transformation on this type
of query, then you might see some partition pruning.

Cheers

Mark

On 04/12/17 17:20, Mark Kirkwood wrote:

On 04/12/17 16:08, Ashutosh Bapat wrote:

On Sun, Dec 3, 2017 at 5:56 AM, legrand legrand
<legrand_legrand@hotmail.com> wrote:

Hello,

I have a typical star schema, having dimension tables "product",
"calendar"
and "country" and a fact table "sales".
This fact table is partitionned by time (range by month) and country
(list).

Will query like:

select product.name, calendar.month, sum(sales.net_price)
from sales
  inner join product on (product.id = sales.cust_id)
  inner join country on (country.id = sales.country_id)
  inner join calendar on (calendar.id = sales.calendar_id)
where
  country.name = 'HERE'
  and calendar.year = '2017'
group by product.name,calendar.month

be able to identify needed partitions ?

AFAIU partition pruning, it works only with the partition key columns.
So, if country.name and calendar.year are the partition keys partition
pruning would identify the needed partitions from those tables. But
planner doesn't know that calendar.year is somehow related to
calendar.id and then transfer that knowledge so that partitions of
sales can be identified.

If you can get your code to perform a star transformation on this type
of query, then you might see some partition pruning.

Actually it won't - sorry. To get that to work, you would need to
evaluate the additional subqueries to produce fixed values! The patch
for 'runtime partition pruning' might be what you want tho.

Cheers

Mark

Thank You !

I will monitor this 'runtime partition pruning' patch.

This will be better than using Partitioned DIM tables "Partion wise joined"
with a multi level partitioned FACT table ;o)

Regards
PAscal

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