Re: Performance issue after creating partitions - Mailing list pgsql-admin

Anyone ever encountered the below situation as what I am noticing with partitions?

Thanks,
Teja. J.

> On Aug 26, 2022, at 11:46 AM, Teja Jakkidi <teja.jakkidi05@gmail.com> wrote:
>
> Thank you, Doug and Malden for your inputs.
>
> As suggested by Doug I tried replacing the trunc() with below command:
> “ order_date >= to_date(..) and order_date < to_date(..) + interval '1' day”
>
> What happens here is: My query has 2tables : A and B, both are having an inner join on company code and order date.
Wehave A.Company_code, A.order_date filter in the where condition which was having trun() previously but now I replaced
itwith the command suggested by Doug. The company_code filter is working for both tables A and B, the query is
searchingonly the partitions particular to that country code. However for order_date condition, the partitions for A
tableare being utilized correctly I.e the query is searching directly in only one partition based on that date. But for
tableB, it is still searching all the partitions, it is not applying the where A.order_date condition for B tables
partitionswhile searching. 
> I do not understand why the A.order_date filter is not being applied to table B where as A.company_code is being
appliedto both tables. 
>
> Thanks and Regards,
> J. Teja Sri.
>
>> On Aug 24, 2022, at 5:52 PM, Doug Reynolds <mav@wastegate.net> wrote:
>>
>> You need to change your query to not use the trunc.  The TRUNC statement forces it to trunc every row in the table.
 
>>
>> If you do order_date >= to_date(..) and order_date < to_date(..) + interval '1' day, it will use the partition range
tonarrow down to the correct partition first. 
>>
>> Sent from my iPhone
>>
>>>> On Aug 24, 2022, at 6:41 PM, Teja Jakkidi <teja.jakkidi05@gmail.com> wrote:
>>>
>>> Hello Admin team,
>>>
>>> We have a Postgres 13 server set up on Google Cloud. Recently we created partitions as below for the tables:
>>> Range on ‘order_date’  column
>>>       List on ‘country_code’ column
>>>
>>> Quarterly partitions for range.
>>>
>>> Order date column is a time stamp column and when we are using this column as a filter in where condition :
trunc(order_date)= to_date(’2022-04-01’,’YYYY-MM-DD’), the query scans all the partitions dated back from the year
2000.So, instead of going to the 2022 Q2 partition directly, the query is scanning all the partitions. 
>>> But when we remove the trunc() function and just specify order_date =‘2022-04-01 07:02:30’, this works as expected.
Itgoes to the correct partition directly and gets the data.  
>>> Can Anyone help me on what’s happening in the first case and why all the partitions are being scanned?
>>> For the first case, when there is a non partition table, it is behaving way better.
>>>
>>> Thanks,
>>> J. Teja.
>>>
>>