Re: Top -N Query performance issue and high CPU usage

On Sat, Jan 31, 2026 at 10:05 PM Ron Johnson <ronljohnsonjr(at)gmail(dot)com>
wrote:

> On Sat, Jan 31, 2026 at 2:47 PM yudhi s <learnerdatabase99(at)gmail(dot)com>
> wrote:
>
>> Thank you.
>>
>>>
>>> 1) Without even looking at the plan I'm going to say 2-VCPU and 16GB RAM
>>> and is insufficient resources for what you want to do.
>>>
>>>
>> Can you please explain a bit in detail, how much minimum VCPU and RAM
>> will be enough resources to suffice this requirement? and you normally do
>> that calculation?
>>
>>
>>> 2) You will need to provide the schema definitions for the tables
>>> involved.
>>>
>>> Do you mean table DDL or just the index definitions on the tables should
>> help?
>>
>> Also i was trying to understand , by just looking into the "explain
>> analyze" output, is there any way we can tie the specific step in the plan
>> , which is the major contributor of the cpu resources? Such that we can
>> then try to fix that part rather than looking throughout the query as its
>> big query?
>>
>
> It looks like 71% (748ms of a total 1056ms) of elapsed time is taken by
> the c_1.tran_date external sort on line 150.
>
> That, obviously, is what you should work on.
>
> 1. You say you increased work_mem. From what, to what?
> 2. But that it did not reduce execution time. Please post the EXPLAIN
> from after increasing work_mem.
> 3. Did you remember to run SELECT pg_reload_conf(); after increasing
> work_mem?
> 4. Is there an index on APP_schema.txn_tbl.tran_date?
>
> And if any suggestion to improve the TOP-N queries where the base table
>> may have many rows in it.
>>
>
>
The DBtune Free Edition <http://app.dbtune.com> can help you find the
correct adjustments for work_mem and other server parameters
<https://dbtune.com/blog/dbtunes-multi-dimensional-performance-tuning-space>.
It's designed to help optimize your PostgreSQL runtime for your current
hardware setup.

> --
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> Don't boil me, I'm still alive.
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>