[GENERAL] Command counter increment vs updating an active snapshot

Hi all, I'm looking into Postgres' internals, and had two quick questions that are related to each other. (1) What's the difference between advancing the command counter and updating an active snapshot? For example, I see that DefineRelation() increments the command counter, but explain.c / copy.

[GENERAL] XLOG's implementation details

Hi all, I am new to Postgres and am interested in XLOG's implementation details. I browsed around the source code, and saw that the particular function that appends XLOG entries is called from multiple places (heap, indexes, transaction subsystem, and so forth). Seeing this, I became particularly