On Thu, Nov 11, 2021 at 12:53 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Thu, Nov 11, 2021 at 9:11 AM Andres Freund <and...@anarazel.de> wrote: > > > > Hi, > > > > On 2021-11-11 12:22:42 +0900, Masahiko Sawada wrote: > > > > 2. > > > > LWLockAcquire(ProcArrayLock, LW_SHARED); > > > > > > > > + flags = proc->statusFlags; > > > > + > > > > + /* > > > > + * If the source xact has any statusFlags, we re-grab ProcArrayLock > > > > + * on exclusive mode so we can copy it to MyProc->statusFlags. > > > > + */ > > > > + if (flags != 0) > > > > + { > > > > + LWLockRelease(ProcArrayLock); > > > > + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); > > > > + } > > > > > > > > > > > > This looks a bit odd to me. It would have been better if we know when > > > > to acquire an exclusive lock without first acquiring the shared lock. > > > > > > I think we should acquire an exclusive lock only if status flags are > > > not empty. But to check the status flags we need to acquire a shared > > > lock. No? > > > > This seems like an unnecessary optimization. ProcArrayInstallRestoredXmin() > > only happens in the context of much more expensive operations. > > > > Fair point. I think that will also make the change in > ProcArrayInstallRestoredXmin() appear neat.
Agreed. This makes me think that it'd be better to copy status flags in a separate function rather than ProcArrayInstallRestoredXmin(). The current patch makes use of the fact that ProcArrayInstallRestoedXmin() acquires a shared lock in order to check the source's status flags. But if we can acquire an exclusive lock unconditionally in this context, it’s clearer to do in a separate function. > > > I think it might be worth asserting that the set of flags we're copying is a > > known subset of the flags that are valid to copy from the source. > > > > Sounds reasonable. +1 Regards, -- Masahiko Sawada EDB: https://www.enterprisedb.com/