While at it also update the comments in walmethods.h to make it less
likely for mistakes like this to appear in the future (thanks to Tom for
improvements to the comments).
And finally, in passing change the return type of walmethod.getlasterror
to being const, also per suggestion from Tom.
Using the name fsync clashed with the #define we have on Windows that
redefines it to _commit. Naming it sync should remove that conflict.
Per all the Windows buildfarm members
This will write the received transaction log into a file called
pg_wal.tar(.gz) next to the other tarfiles instead of writing it to
base.tar. When using fetch mode, the transaction log is still written to
base.tar like before, and when used against a pre-10 server, the file
is named pg_xlog.tar.
To do this, implement a new concept of a "walmethod", which is
responsible for writing the WAL. Two implementations exist, one that
writes to a plain directory (which is also used by pg_receivexlog) and
one that writes to a tar file with optional compression.
Reviewed by Michael Paquier
Magnus Hagander
Bruce Momjian