Consider (from test_insert.py) the following query:
create table foo as select repeat('AZ', 128 * 1024 * 1024) as s
repeat() gets constant-folded into a 256MB expression payload, which is then transmitted to every fragment instance that evaluates the expression. This can lead to timeouts.
The workaround is ENABLE_EXPR_REWRITES=0.
It's not obvious what the answer is - should the FE be aware of the serialized size of an expression when deciding whether to constant fold it?