A few questions:

Christopher Kings-Lynne wrote:

1. Did that fix to not allow cluster on partial and non-null indexes get
backpatched?

Yes, I see it in 7.3.X CVS.

2. How can I deliberately cause a deadlock in order to test some code?

Sure:

CREATE TABLE t1(x int);
CREATE TABLE t2(x int);
INSERT INTO t1 VALUES (1);
INSERT INTO t2 VALUES (1);

CLIENT 1:
BEGIN;
UPDATE t1 SET x=2;

CLIENT 2:
BEGIN;
UPDATE t2 SET x=2;
UPDATE t1 SET x=1; -- blocks

CLIENT 1:
UPDATE t2 SET x=2;

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