Function XLogRecordPageWithFreeSpace

src/backend/storage/freespace/freespace.c:199–225

* XLogRecordPageWithFreeSpace - like RecordPageWithFreeSpace, for use in * WAL replay */

 *		WAL replay
 */
void
XLogRecordPageWithFreeSpace(RelFileNode rnode, BlockNumber heapBlk,
							Size spaceAvail)
{
	int			new_cat = fsm_space_avail_to_cat(spaceAvail);
	FSMAddress	addr;
	uint16		slot;
	BlockNumber blkno;
	Buffer		buf;
	Page		page;

	/* Get the location of the FSM byte representing the heap block */
	addr = fsm_get_location(heapBlk, &slot);
	blkno = fsm_logical_to_physical(addr);

	/* If the page doesn't exist already, extend */
	buf = XLogReadBufferExtended(rnode, FSM_FORKNUM, blkno, RBM_ZERO_ON_ERROR);
	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);

	page = BufferGetPage(buf);
	if (PageIsNew(page))
		PageInit(page, BLCKSZ, 0);

	if (fsm_set_avail(page, slot, new_cat))
		MarkBufferDirtyHint(buf, false);
	UnlockReleaseBuffer(buf);
}

/*
 * GetRecordedFreeSpace - return the amount of free space on a particular page,