Horton

Re: Fix missing EvalPlanQual recheck for TID scans

Sophie Alpert <pg@sophiebits.com>

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From: "Sophie Alpert" <pg@sophiebits.com>
To: "Chao Li" <li.evan.chao@gmail.com>
Cc: "David Rowley" <dgrowleyml@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-09-14T03:02:00Z
Lists: pgsql-hackers 
On Sat, Sep 13, 2025 at  3:12 PM, Sophie Alpert <pg@sophiebits.com> wrote:
> And indeed, like I mentioned in my previous message, my isolation test 
> `permutation tid1 tidsucceed2 c1 c2 read` from eval-plan-qual.spec in 
> my patch will fail if Recheck were to return false in this case. Though 
> somewhat contrived, you can imagine this happening with multiple 
> sessions driven by the same application:

Another case where returning FALSE does not give the correct behavior is when two relations are involved, only one of which is modified:

S1: BEGIN;
S2: BEGIN;
S1: UPDATE accounts SET balance = balance + 100 WHERE ctid = '(0,1)' RETURNING accountid, balance;
S2: SELECT * FROM accounts JOIN accounts_ext USING (accountid) WHERE accounts_ext.ctid = '(0,1)' FOR UPDATE OF accounts;
S1: COMMIT;
S2: COMMIT;

In my patch the S2 query correctly returns one row, whereas with your proposed change it incorrectly returns none.

accountid|balance|balance2|balance|other|newcol|newcol2
---------+-------+--------+-------+-----+------+-------
checking |    700|    1400|    600|other|    42|       

Sophie

Commits

  1. Add missing EPQ recheck for TID Range Scan

  2. Add missing EPQ recheck for TID Scan

  3. Repair problems with EvalPlanQual where target table is scanned as

  4. Tid access method feature from Hiroshi Inoue, Inoue@tpf.co.jp