On Thu, May 26, 2022 at 12:53 PM Michael Paquier <mich...@paquier.xyz> wrote: > > On Tue, May 24, 2022 at 04:52:50PM -0700, Andres Freund wrote: > > > 2) xid wraparound. There's nothing forcing SubTransGetTopmostTransaction() > > to > > be called regularly, so even if a backend isn't idle, the cache could > > just > > get more and more outdated until hitting wraparound > > Hence, you mean that the non-regularity of the call makes it more > exposed to an inconsistent result after a wraparound? >
Won't in theory the similar cache in transam.c is also prone to similar behavior? Anyway, how about if we clear this cache for subtrans whenever TransactionXmin is advanced and cachedFetchSubXid precedes it? The comments atop SubTransGetTopmostTransaction seem to state that we don't care about the exact topmost parent when the intermediate one precedes TransactionXmin. I think it should preserve the optimization because anyway for such cases there is a fast path in SubTransGetTopmostTransaction. -- With Regards, Amit Kapila.
