This class is used to track the active procedures when loading procedures from proc wal file.
We will read proc wal files from new to old, but when reading a proc wal file, we will still read
from top to bottom, so there are two groups of methods for this class.
The first group is
. It is used
when reading a proc wal file. In these methods, for the same procedure, typically the one comes
later should win, please see the comment for
to see the
The second group is
. We will have a global
to hold global the active procedures, and a local
to hold the active procedures for the current proc wal file. And when we finish reading a proc
wal file, we will merge the local one into the global one, by calling the
method of the global one and pass the local one in. In this
method, for the same procedure, the one comes earlier will win, as we read the proc wal files
from new to old(the reverse order).