Are transposition tables (in engines) used for one or multiple games?
My current knowledge of transposition tables is that when an engine searches the game tree, there will sometimes be positions that have already been calculated earlier. A transposition table allows an engine to take what it already had calculated earlier and use it for even deeper search.
What I don't understand is whether transposition tables store positions permanently (such that an engine can use what it previously calculated in previous games for new games) or if it's strictly game-specific as in that a new game corresponds with a completely empty and new transposition table.