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From: Jeff Davis <[email protected]>
To: [email protected]
Subject: ALTER FOREIGN DATA WRAPPER can drop dependency on handler
Date: Wed, 18 Mar 2026 12:09:54 -0700
Message-ID: <[email protected]> (raw)


CREATE FUNCTION test_fdw_handler()
    RETURNS fdw_handler
    AS :'regresslib', 'test_fdw_handler'
    LANGUAGE C;

CREATE FOREIGN DATA WRAPPER test_fdw HANDLER test_fdw_handler;

-- correctly raises dependency ERROR
DROP FUNCTION test_fdw_handler;

ALTER FOREIGN DATA WRAPPER test_fdw VALIDATOR postgresql_fdw_validator;

-- fails to raise dependency error ERROR
DROP FUNCTION test_fdw_handler;


Patch attached.

Note: I found this while investigating a related issue for the FDW
connection function, with patch here:

https://www.postgresql.org/message-id/[email protected]

I am keeping this patch separate for a clean backport.

Regards,
	Jeff Davis



Attachments:

  [text/x-patch] v1-0001-Fix-dependency-on-FDW-handler.patch (935B, 2-v1-0001-Fix-dependency-on-FDW-handler.patch)
  download | inline diff:
From bf7685cbda2c885fcc6b9aecf11da5c8898db496 Mon Sep 17 00:00:00 2001
From: Jeff Davis <[email protected]>
Date: Wed, 18 Mar 2026 11:52:15 -0700
Subject: [PATCH v1] Fix dependency on FDW handler.

ALTER FOREIGN DATA WRAPPER could drop the dependency on the handler
function if it wasn't explicitly specified.
---
 src/backend/commands/foreigncmds.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/backend/commands/foreigncmds.c b/src/backend/commands/foreigncmds.c
index 45681235782..0b31afd8a79 100644
--- a/src/backend/commands/foreigncmds.c
+++ b/src/backend/commands/foreigncmds.c
@@ -786,6 +786,11 @@ AlterForeignDataWrapper(ParseState *pstate, AlterFdwStmt *stmt)
 		ereport(WARNING,
 				(errmsg("changing the foreign-data wrapper handler can change behavior of existing foreign tables")));
 	}
+	else
+	{
+		/* handler unchanged */
+		fdwhandler = fdwForm->fdwhandler;
+	}
 
 	if (validator_given)
 	{
-- 
2.43.0

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