Hi again,
I continued investigating the planner path for an ANY SubLink and traced it
with GDB.
For the following query:
EXPLAIN (VERBOSE, COSTS)
SELECT *
FROM pg_class c
WHERE c.oid = ANY (
SELECT oid
FROM pg_namespace
);
the resulting plan is a Hash Join with:
Hash Cond: (c.oid = pg_namespace.oid)
I placed a breakpoint in convert_ANY_sublink_to_join() and confirmed that
the query reaches this function through:
standard_planner
-> subquery_planner
-> pull_up_sublinks
-> pull_up_sublinks_jointree_recurse
-> pull_up_sublinks_qual_recurse
-> convert_ANY_sublink_to_join
At the breakpoint:
sublink->subLinkType = ANY_SUBLINK
under_not = false
The function constructs a JoinExpr with:
jointype = JOIN_SEMI
The generated join has the pulled-up subquery as its rarg, while the
comparison is represented by an OpExpr.
I also checked the operator OID from the generated OpExpr:
opno = 607
and confirmed through pg_operator that it is:
607 | = | oid | oid
So the transformation at this stage is effectively:
c.oid = ANY (SELECT oid FROM pg_namespace)
↓
JOIN_SEMI
condition: c.oid = pg_namespace.oid
One useful distinction I confirmed is that convert_ANY_sublink_to_join()
itself creates the logical JOIN_SEMI; it does not directly select the
physical Hash Join shown by EXPLAIN. The physical join implementation is
selected later in planning.
My next step would be to trace the resulting JOIN_SEMI further into the
join-planning path and identify where the physical Hash Join is selected.
Sharing this as an investigation update in case there are particular
planner functions you would recommend tracing next.
Regards,
Osama
On Fri, Sep 25, 2026 at 6:53 AM Osama Abdul Qader <
[email protected]> wrote:
> Hi Andres and Wei
>
> Thanks for the additional context. That makes the use case much cleaner.
>
> I understand that the original optimization of skipping the EPQ recheck
> for constant assignments is not valid, and I’ll consider that direction
> closed.
>
> I’ll continue investigating the implementation side instead: specifically,
> how expensive SubPlans are re-executed during repeated EPQ rechecks,
> whether they depend on the EPQ tuple, and whether any independent work can
> be safely reused while preserving the required Read Committed semantics.
>
> I’ll also keep the broader batch-update use case in mind rather than
> optimizing only for the current reproducer.
>
> Regards
> Osama Abdul Qader.
>
> On Tue, Sep 22, 2026 at 7:45 AM Wei Sun <[email protected]> wrote:
>
>> Hi
>>
>>
>> >This is obviously an intentionally bad query. Before we add even one more
>> >iota
>>
>> >of additional complexity to EPQ, we need a *lot* more convincing use cases
>>
>> >than this. What is the real scenario in which you are updating huge numbers
>>
>> >of rows that also have been updated in another transaction, with a subquery
>> >not implemented as a join?
>>
>> The background of the issue is a business function in which developers
>> use an
>> UPDATE statement containing complex subqueries to perform batch data
>> updates,
>> and the performance of these subqueries is poor. This feature may be
>> called concurrently,
>> causing two updates to update the same part of the data, ultimately
>> resulting in the scenario
>> I described.This problem can indeed be solved by rewriting SQL, I'm just
>> not sure if there's
>> a better way to implement EPQ in this scenario.
>>
>>
>> >I don't think that's correct in this case. The other session could very well
>> >have updated deal_no to not match
>> >
>> deal_no IN (SELECT deal_no FROM bond_deal_detail ORDER BY deal_no LIMIT
>> 100000)
>> >anymore.
>>
>> Your judgment was correct, and I later became aware of this issue and
>> rejected this idea in subsequent emails.
>>
>>
>> Regards,
>> Wei Sun
>>
>> 原始邮件
>> ------------------------------
>> 发件人：Andres Freund <[email protected]>
>> 发件时间：2026年9月22日 02:58
>> 收件人：Wei Sun <[email protected]>, Osama Abdul Qader <
>> [email protected]>
>> 抄送：pgsql-hackers <[email protected]>
>> 主题：Re: Severe performance degradation with concurrent updates due to
>> excessive EvalPlanQual (EPQ) re‑evaluation
>>
>> Hi,
>>
>> On 2026-09-15 16:05:46 +0800, Wei Sun wrote:
>> > I encountered a serious performance regression when running concurrent
>> > UPDATE statements targeting the same set of rows on PostgreSQL 18.1.
>> > The second update session runs extremely slow due to excessive
>> > EvalPlanQual (EPQ) re‑evaluation logic.
>> > [...]
>>
>> > ## Test setup
>> > Create test table and populate 1000000 rows of mock bond trading data,
>> > no user‑defined indexes (only identity primary key on `id`).
>>
>> > Then create a copy table `bond_deal_detail_sw` for concurrent update tests.
>> > This issue occurs when read committed isolation level.
>> > Session 1:
>> > EXPLAIN ANALYZE UPDATE bond_deal_detail_sw
>> > SET deal_price = 26915
>>
>> > WHERE deal_no IN (SELECT deal_no FROM bond_deal_detail ORDER BY deal_no
>> > LIMIT 100000);
>>
>>
>> This is obviously an intentionally bad query. Before we add even one more
>> iota
>> of additional complexity to EPQ, we need a *lot* more convincing use cases
>>
>> than this. What is the real scenario in which you are updating huge numbers
>>
>> of rows that also have been updated in another transaction, with a subquery
>> not implemented as a join?
>>
>>
>>
>> > since the target update value is a constant and does not reference any
>> > column of the updated table,
>> > logically there is no need to recompute the target new value via EPQ for
>> > these rows.
>>
>>
>> I don't think that's correct in this case. The other session could very well
>> have updated deal_no to not match
>>
>> deal_no IN (SELECT deal_no FROM bond_deal_detail ORDER BY deal_no LIMIT
>> 100000)
>> anymore.
>>
>> Greetings,
>>
>> Andres Freund
>>
>>
>>
