Instead of thinking in terms of 'latest' and 'lsn' of the request,
each request has two LSNs: the request LSN and 'not_modified_since'
LSN. The request is nominally made at the request LSN, that determines
what page version we want to see. But as a hint, we also include
'not_modified_since'. It tells the pageserver that the page has not
been modified since that LSN, which allows the pageserver to skip
waiting for newer WAL to arrive, and could allow more optimizations in
the future.
Refactor the internal functions to calculate the request LSN to
calculate both LSNs.
Sending two LSNs to the pageserver requires using the new protocol
version 2. The previous commit added the server support for it, but we
still default to the old protocol for compatibility with old
pageservers. The 'neon.protocol_version' GUC can be used to use the
new protocol.
The new protocol addresses one cause of issue #6211, although you can
still get the same error if you have a standby that is lagging behind
so that the page version it needs is genuinely GC'd away.
* Extract neon and neon_test_utils from postgres repo
* Remove neon from vendored postgres repo, and fix build_and_test.yml
* Move EmitWarningsOnPlaceholders to end of _PG_init in neon.c (from libpagestore.c)
* Fix Makefile location comments
* remove Makefile EXTRA_INSTALL flag
* Update Dockerfile.compute-node to build and include the neon extension
