* Actual generation logic is in a separate crate `postgres_ffi/wal_generate`
* The create also provides a binary for debug purposes akin to `initdb`
* Two tests currently fail and are ignored
* There is no easy way to test this directly in Safekeeper as it starts restoring from commit_lsn.
So testing would require disconnecting Safekeeper just after it has received the WAL,
but before it is committed.
* Do not set LSN for new FPI page
refer #1656
* Add page_is_new, page_get_lsn, page_set_lsn functions
* Fix page_is_new implementation
* Add comment from XLogReadBufferForRedoExtended
A new `get_lsn_by_timestamp` command is added to the libpq page service
API.
An extra timestamp field is now stored in an extra field after each
Clog page. It is the timestamp of the latest commit, among all the
transactions on the Clog page. To find the overall latest commit, we
need to scan all Clog pages, but this isn't a very frequent operation
so that's not too bad.
To find the LSN that corresponds to a timestamp, we perform a binary
search. The binary search starts with min = last LSN when GC ran, and
max = latest LSN on the timeline. On each iteration of the search we
check if there are any commits with a higher-than-requested timestamp
at that LSN.
Implements github issue 1361.
