> Forgive me for being dense, but what is there to stop you using a > CopySnapshot in TopMemoryContext? If you did, there would be no way to > free it, nor would we notice it had been done, AFAICS. Not anything I'm > thinking about doing, though.
Well, TopMemoryContext is no good because we want to free snapshots in a fell swoop at transaction abort. TopTransactionContext would be OK, as I just said in the parallel subthread.