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From: [email protected]
To: [email protected]
To: [email protected]
Subject: UPDATE operation terminates logical replication receiver process due to an assertion
Date: Thu, 12 Jan 2023 13:23:57 +0300
Message-ID: <[email protected]> (raw)

Dear all,

I think I've found a problem in logical replication that was introduced 
recently in the patch:

Fix calculation of which GENERATED columns need to be updated
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=3f7836ff651ad710fef52fa87b248ecdfc646...

There is an assertion which accidentally terminates logical replication 
worker process. The assertion was introduced in the patch. To reproduce 
the problem Postgres should be compiled with enabled assertions. The 
problem appears when executing UPDATE operation on a non-empty table 
with GENERATED columns and a BEFORE UPDATE trigger. The problem seems to 
appear on the latest snapshots of 13 and 14 versions (sorry, I haven't 
tested other versions).

Stack:
------
TRAP: FailedAssertion("relinfo->ri_GeneratedExprs != NULL", File: 
"execUtils.c", Line: 1292)
postgres: logical replication worker for subscription 16401 
(ExceptionalCondition+0x89)[0x55838760b902]
postgres: logical replication worker for subscription 16401 
(ExecGetExtraUpdatedCols+0x90)[0x558387314bd8]
postgres: logical replication worker for subscription 16401 
(ExecGetAllUpdatedCols+0x1c)[0x558387314c20]
postgres: logical replication worker for subscription 16401 
(ExecUpdateLockMode+0x19)[0x558387306ce3]
postgres: logical replication worker for subscription 16401 
(ExecBRUpdateTriggers+0xc7)[0x5583872debe8]
postgres: logical replication worker for subscription 16401 
(ExecSimpleRelationUpdate+0x122)[0x55838730dca7]
postgres: logical replication worker for subscription 16401 
(+0x43d32f)[0x55838745632f]
postgres: logical replication worker for subscription 16401 
(+0x43e382)[0x558387457382]
postgres: logical replication worker for subscription 16401 
(+0x43e5d3)[0x5583874575d3]
postgres: logical replication worker for subscription 16401 
(+0x43e76b)[0x55838745776b]
postgres: logical replication worker for subscription 16401 
(ApplyWorkerMain+0x3ac)[0x558387457e8b]
postgres: logical replication worker for subscription 16401 
(StartBackgroundWorker+0x253)[0x5583874157ed]
postgres: logical replication worker for subscription 16401 
(+0x40e9c9)[0x5583874279c9]
postgres: logical replication worker for subscription 16401 
(+0x40eb43)[0x558387427b43]
postgres: logical replication worker for subscription 16401 
(+0x40fd28)[0x558387428d28]
/lib/x86_64-linux-gnu/libc.so.6(+0x42520)[0x7f08cd44b520]
/lib/x86_64-linux-gnu/libc.so.6(__select+0xbd)[0x7f08cd52474d]
postgres: logical replication worker for subscription 16401 
(+0x410ceb)[0x558387429ceb]
postgres: logical replication worker for subscription 16401 
(PostmasterMain+0xbf3)[0x55838742ac4d]
postgres: logical replication worker for subscription 16401 
(main+0x20c)[0x55838736076d]
/lib/x86_64-linux-gnu/libc.so.6(+0x29d90)[0x7f08cd432d90]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80)[0x7f08cd432e40]

How to reproduce:
-----------------
1. Create master-replica configuration with enabled logical replication. 
The initial schema is shown below:

CREATE TABLE gtest26 (
  a int PRIMARY KEY,
  b int GENERATED ALWAYS AS (a * 2) STORED
  );

CREATE FUNCTION gtest_trigger_func() RETURNS trigger
  LANGUAGE plpgsql
  AS $$
  BEGIN
  IF tg_op IN ('DELETE', 'UPDATE') THEN
  RAISE INFO '%: %: old = %', TG_NAME, TG_WHEN, OLD;
  END IF;
  IF tg_op IN ('INSERT', 'UPDATE') THEN
  RAISE INFO '%: %: new = %', TG_NAME, TG_WHEN, NEW;
  END IF;
  IF tg_op = 'DELETE' THEN
  RETURN OLD;
  ELSE
  RETURN NEW;
  END IF;
  END
  $$;

CREATE TRIGGER gtest1 BEFORE DELETE OR UPDATE ON gtest26
  FOR EACH ROW
  WHEN (OLD.b < 0) -- ok
  EXECUTE PROCEDURE gtest_trigger_func();

INSERT INTO gtest26(a) values (-2), (0), (3)

2. The problem appears if to execute the following sql on the master 
node:

UPDATE gtest26 SET a = a + 1;

I'm not sure that this assertion is the proper one and how to properly 
fix the issue. That's why I'm asking for some help of the community. 
Thank you in advance.

With best regards,
Vitaly

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