Locking issue with concurrent DELETE / INSERT in PostgreSQL

This is pretty simple, but I'm baffled by what PG does (v9.0). We start with a simple table: CREATE TABLE test (id INT PRIMARY KEY); and a few rows: INSERT INTO TEST VALUES (1); INSERT INTO TEST VALUES (2); Using my favorite JDBC query tool (ExecuteQuery), I connect two session windows to the db where this table lives. Both of them are transactional (ie, auto-commit=false). Let's call them S1 and S2. The same bit of code for each: 1:DELETE FROM test WHERE id=1; 2:INSERT INTO test VALUES (1); 3:COMMIT; Now, run this in slow motion, executing one at a time in the windows. S1-1 runs (1 row deleted) S2-1 runs (but is blocked since S1 has a write lock) S1-2 runs (1 row inserted) S1-3 runs, releasing the write lock S2-1 runs, now that it can get the lock. But reports 0 rows deleted. HUH??? S2-2 runs, reports a unique key constraint violation Now, this works fine in SQLServer. When S2 does the delete, it reports 1 row deleted. And then S2's insert works fine. I suspect that PostgreSQL is locking the index in the table where that row exists, whereas SQLServer locks the actual key value. Am I right? Can this be made to work?