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help / color / mirror / Atom feedFrom: Ron Johnson <[email protected]>
To: pgsql-general <[email protected]>
Subject: Re: Top -N Query performance issue and high CPU usage
Date: Sat, 31 Jan 2026 16:05:17 -0500
Message-ID: <CANzqJaD5gfNufOXe0LMuxhN_goHRSTt2MJo3oQNUbaiO=cph_w@mail.gmail.com> (raw)
In-Reply-To: <CAEzWdqd6LAHs+FiFeJLqDTS-QBLq6+foE1-mgBC9AXVpFmVnZg@mail.gmail.com>
References: <CAEzWdqd0SPkZMYNaAbERdgczkfQqLmNV5JBMmF-F9s7KjxJ0gw@mail.gmail.com>
<[email protected]>
<CAEzWdqd6LAHs+FiFeJLqDTS-QBLq6+foE1-mgBC9AXVpFmVnZg@mail.gmail.com>
On Sat, Jan 31, 2026 at 2:47 PM yudhi s <[email protected]> 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.
>
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
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Subject: Re: Top -N Query performance issue and high CPU usage
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