On Sun, Mar 8, 2020 at 7:58 AM Masahiko Sawada < masahiko.saw...@2ndquadrant.com> wrote:
> On Mon, 24 Feb 2020 at 19:08, Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > On Thu, Feb 20, 2020 at 8:06 AM Andres Freund <and...@anarazel.de> > wrote: > > > > > > Hi, > > > > > > On 2020-02-19 11:12:18 +0530, Amit Kapila wrote: > > > > I think till we know the real need for changing group locking, going > > > > in the direction of what Tom suggested to use an array of LWLocks [1] > > > > to address the problems in hand is a good idea. > > > > > > -many > > > > > > I think that building yet another locking subsystem is the entirely > > > wrong idea - especially when there's imo no convincing architectural > > > reasons to do so. > > > > > > > Hmm, AFAIU, it will be done by having an array of LWLocks which we do > > at other places as well (like BufferIO locks). I am not sure if we > > can call it as new locking subsystem, but if we decide to continue > > using lock.c and change group locking then I think we can do that as > > well, see my comments below regarding that. > > > > > > > > > It is not very clear to me that are we thinking to give up on Tom's > > > > idea [1] and change group locking even though it is not clear or at > > > > least nobody has proposed an idea/patch which requires that? Or are > > > > we thinking that we can do what Tom suggested for relation extension > > > > lock and also plan to change group locking for future parallel > > > > operations that might require it? > > > > > > What I'm advocating is that extension locks should continue to go > > > through lock.c. And yes, that requires some changes to group locking, > > > but I still don't see why they'd be complicated. > > > > > > > Fair position, as per initial analysis, I think if we do below three > > things, it should work out without changing to a new way of locking > > for relation extension or page type locks. > > a. As per the discussion above, ensure in code we will never try to > > acquire another heavy-weight lock after acquiring relation extension > > or page type locks (probably by having Asserts in code or maybe some > > other way). > > The current patch > (v02_0001-Added-assert-to-verify-that-we-never-try-to-take-any.patch) > doesn't check that acquiring a heavy-weight lock after page type lock, > is that right? No, it should do that. > There is the path doing that: ginInsertCleanup() holds > a page lock and insert the pending list items, which might hold a > relation extension lock. > Right, I could also see that, but do you see any problem with that? I agree that Assert should cover this case, but I don't see any fundamental problem with that. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
