protected static DBTraceSpaceKey unpackRegSpaceKey(AddressSpace space,
			DBTraceThreadManager threadManager, long id) {
		long threadKey = unpackRegThread(id);
		TraceThread thread = threadManager.getThread(threadKey);
		assert thread != null;
		int frameLevel = unpackRegFrame(id);
		return DBTraceSpaceKey.create(space, thread, frameLevel);
	}
For non-register space:

{@code
+---12----+----52----+
| SpaceID |    Key   |
+---------+----------+
}

For register space:

{@code
+---12----+----32----+----8----+--12--+
| SpaceID |  Thread  |  Frame  |  Key |
+---------+----------+---------+------+
}
Ghidra/Debug/Framework-TraceModeling/src/main/java/ghidra/trace/database/bookmark/DBTraceBookmarkManager.java