Function XLogBeginInsert

src/backend/access/transam/xloginsert.c:131–146

* Begin constructing a WAL record. This must be called before the * XLogRegister* functions and XLogInsert(). */

 * XLogRegister* functions and XLogInsert().
 */
void
XLogBeginInsert(void)
{
	Assert(max_registered_block_id == 0);
	Assert(mainrdata_last == (XLogRecData *) &mainrdata_head);
	Assert(mainrdata_len == 0);

	/* cross-check on whether we should be here or not */
	if (!XLogInsertAllowed())
		elog(ERROR, "cannot make new WAL entries during recovery");

	if (begininsert_called)
		elog(ERROR, "XLogBeginInsert was already called");

	begininsert_called = true;
}

/*
 * Ensure that there are enough buffer and data slots in the working area,