[ozgune]

(Ozgun from Citus Data)

In the blog post, I used the + operator and sum() aggregate function interchangeably to be brief. Actually, those two operations are related, but have different representations in distributed relational algebra. I updated the first footnote in the post to reflect that.

For your comment, we have in fact two questions. First, is the ExtendedOp commutative with the Collect operator? Second, if it isn't, what properties do our transformations need to respect so that we can pull up the Collect? (equivalence property and associativity)

It's hard to be comprehensive about distributed relational algebra in a blog post. For example, the given logical tree doesn't have enough operator primitives to express large table joins. If you'd like, I'd be happy to get together and chat more about the details.