After populating the stock_tmp table, i'm running these SQL queries via legacy mysqli wrapper code. I don't think this code needs additional locks to prevent people from seeing incorrect data. Is that correct?
DELETE FROM stock WHERE ean NOT IN (SELECT ean FROM stock_tmp);
REPLACE INTO stock SELECT * FROM stock_tmp;
INSERT INTO stock SELECT * FROM stock_tmp AS tmp
ON DUPLICATE KEY UPDATE ean=tmp.ean, etc=tmp.etc;
Is 10+% faster than REPLACE INTO and does not change all AUTO_INCREMENT data. Source.
10+ times faster is this:
RENAME TABLE stock TO stock_swp,
stock_tmp TO stock,
stock_swp TO stock_tmp;
The implied locking should be sufficient in any case.