Function XLogRegisterBuffer

src/backend/access/transam/xloginsert.c:228–275

* Register a reference to a buffer with the WAL record being constructed. * This must be called for every page that the WAL-logged operation modifies. */

 * This must be called for every page that the WAL-logged operation modifies.
 */
void
XLogRegisterBuffer(uint8 block_id, Buffer buffer, uint8 flags)
{
	registered_buffer *regbuf;

	/* NO_IMAGE doesn't make sense with FORCE_IMAGE */
	Assert(!((flags & REGBUF_FORCE_IMAGE) && (flags & (REGBUF_NO_IMAGE))));
	Assert(begininsert_called);

	if (block_id >= max_registered_block_id)
	{
		if (block_id >= max_registered_buffers)
			elog(ERROR, "too many registered buffers");
		max_registered_block_id = block_id + 1;
	}

	regbuf = &registered_buffers[block_id];

	BufferGetTag(buffer, &regbuf->rnode, &regbuf->forkno, &regbuf->block);
	regbuf->page = BufferGetPage(buffer);
	regbuf->flags = flags;
	regbuf->rdata_tail = (XLogRecData *) &regbuf->rdata_head;
	regbuf->rdata_len = 0;

	/*
	 * Check that this page hasn't already been registered with some other
	 * block_id.
	 */
#ifdef USE_ASSERT_CHECKING
	{
		int			i;

		for (i = 0; i < max_registered_block_id; i++)
		{
			registered_buffer *regbuf_old = &registered_buffers[i];

			if (i == block_id || !regbuf_old->in_use)
				continue;

			Assert(!RelFileNodeEquals(regbuf_old->rnode, regbuf->rnode) ||
				   regbuf_old->forkno != regbuf->forkno ||
				   regbuf_old->block != regbuf->block);
		}
	}
#endif

	regbuf->in_use = true;
}

/*
 * Like XLogRegisterBuffer, but for registering a block that's not in the