AlterSubscription_refresh: avoid stomping on global variable

This patch replaces use of the global "wrconn" variable in
AlterSubscription_refresh with a local variable of the same name, making
it consistent with other functions in subscriptioncmds.c (e.g.
DropSubscription).

The global wrconn is only meant to be used for logical apply/tablesync worker.
Abusing it this way is known to cause trouble if an apply worker
manages to do a subscription refresh, such as reported by Jeremy Finzel
and diagnosed by Andres Freund back in November 2020, at
https://www.postgresql.org/message-id/20201111215820[email protected]

Backpatch to 10.  In branch master, also move the connection establishment
to occur outside the PG_TRY block; this way we can remove a test for NULL in
PG_FINALLY, and it also makes the code more consistent with similar code in
the same file.

Author: Peter Smith <[email protected]>
Reviewed-by: Bharath Rupireddy <[email protected]>
Reviewed-by: Japin Li <[email protected]>
Discussion: https://postgr.es/m/CAHut+Pu7Jv9L2BOEx_Z0UtJxfDevQSAUW2mJqWU+CtmDrEZVAg@mail.gmail.com

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e927b048d6eb465b2cfbde82797f384dac8641a3..f05e86fa93648969ed0bdd42deb2640240faad33 100644 (file)
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -507,6 +507,7 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data)
    List       *subrel_states;
    Oid        *subrel_local_oids;
    Oid        *pubrel_local_oids;
+   WalReceiverConn *wrconn;
    ListCell   *lc;
    int         off;
 
@@ -821,7 +822,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
    char        originname[NAMEDATALEN];
    char       *err = NULL;
    RepOriginId originid;
-   WalReceiverConn *wrconn = NULL;
+   WalReceiverConn *wrconn;
    StringInfoData cmd;
 
    /*