Re: WIP: Access method extendability

In general pattern of generic WAL usage is following.

1) Start using generic WAL: specify relation

M-m, what about extensions which wants to use WAL but WAL record doesn't connected to any relation? For example, transaction manager or kind of FDW.

GenericXLogStart(index);

2) Register buffers

GenericXLogRegister(0, buffer1, false);
GenericXLogRegister(1, buffer2, true);

first argument is a slot number, second is the buffer, third is flag indicating
new buffer

Why do we need a slot number? to replace already registered buffer?