Re: Performance Issue with Hash Partition Query Execution in PostgreSQL 16

Sorry, it was typo. Bind variable is bigint only.

Thanks

On Fri, 8 Nov, 2024, 7:09 pm David Mullineux, <dmullx(at)gmail(dot)com> wrote:

> Just spotted a potential problem. The indexed column is a bigint. Are you,
> in your prepared statement passing a string or a big int ?
> I notice your plan is doing an implicit type conversion when you run it
> manually.
> Sometimes the wrong type will make it not use the index.
>
> On Fri, 8 Nov 2024, 03:07 ravi k, <ravisql09(at)gmail(dot)com> wrote:
>
>> Hi ,
>>
>> Thanks for the suggestions.
>>
>> Two more observations:
>>
>> 1) no sequence scan noticed from pg_stat_user_tables ( hope stats are
>> accurate in postgres 16) if parameter sniffing happens the possibility of
>> going to sequence scan is more right.
>>
>> 2) no blockings or IO issue during the time.
>>
>> 3) even with limit clause if touch all partitions also it could have been
>> completed in milliseconds as this is just one record.
>>
>> 4) auto_explain in prod we cannot enable as this is expensive and with
>> high TPS we may face latency issues and lower environment this issue cannot
>> be reproduced,( this is happening out of Million one case)
>>
>> This looks puzzle to us, just in case anyone experianced pls share your
>> experience.
>>
>> Regards,
>> Ravi
>>
>> On Thu, 7 Nov, 2024, 3:41 am David Mullineux, <dmullx(at)gmail(dot)com> wrote:
>>
>>> It might be worth eliminating the use of cached plans here. Is your app
>>> using prepared statements at all?
>>> Point is that if the optimizer sees the same prepared query , 5 times,
>>> the it locks the plan that it found at that time. This is a good trade off
>>> as it avoids costly planning-time for repetitive queries. But if you are
>>> manually querying, the a custom plan will be generated anew.
>>> A quick analyze of the table should reset the stats and invalidate any
>>> cached plans.
>>> This may not be your problem just worth eliminating it from the list of
>>> potential causes.
>>>
>>> On Wed, 6 Nov 2024, 17:14 Ramakrishna m, <ram(dot)pgdb(at)gmail(dot)com> wrote:
>>>
>>>> Hi Team,
>>>>
>>>> One of the queries, which retrieves a single record from a table with
>>>> 16 hash partitions, is taking more than 10 seconds to execute. In contrast,
>>>> when we run the same query manually, it completes within milliseconds. This
>>>> issue is causing exhaustion of the application pools. Do we have any bugs
>>>> in postgrs16 hash partitions? Please find the attached log, table, and
>>>> execution plan.
>>>>
>>>> size of the each partitions : 300GB
>>>> Index Size : 12GB
>>>>
>>>> Postgres Version : 16.x
>>>> Shared Buffers : 75 GB
>>>> Effective_cache : 175 GB
>>>> Work _mem : 4MB
>>>> Max_connections : 3000
>>>>
>>>> OS : Ubuntu 22.04
>>>> Ram : 384 GB
>>>> CPU : 64
>>>>
>>>> Please let us know if you need any further information or if there are
>>>> additional details required.
>>>>
>>>>
>>>> Regards,
>>>> Ram.
>>>>
>>>