Re: Re: GiST optimizing memmoves in gistplacetopage for fixed-size updates [PoC]

>If a feature changes the shape of WAL records, XLOG_PAGE_MAGIC is bumped to prevent any problems.
I've attached patch with a bump, but, obviously, it'll be irrelevant
after any other commit changing WAL shape.

Here is a patch with updated GiST README.
I haven't found apropriate place to describe PageIndexTupleOverwrite
function in docs, since all it's siblings are described only in the
code.
Code comments describing this function are coherent with others
(PageAddItem, PageIndexTupleDelete).

Best regards, Andrey Borodin, Octonica & Ural Federal University.