When we do things like:

SELECT t2.id, t1.val from T1 JOIN T2 ON t1.id=t2.id

looks like using t1.id instead makes it use lot less memory as the page from lhs is left undisturbed. We have seen local OOMs with this kind of construcs.

But if you change it to the equivalent:

SELECT t1.id, t1.val from T1 JOIN T2 ON t1.id=t2.id

it works a lot better