Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager - Mailing list pgsql-hackers
From | Dilip Kumar |
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Subject | Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager |
Date | |
Msg-id | CAFiTN-s5wxeCbQhhbhYxmS2uTNKK0MULfJxNnPHKw2HO1qMKUQ@mail.gmail.com Whole thread Raw |
In response to | Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager (Mahendra Singh Thalor <mahi6run@gmail.com>) |
Responses |
Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager
Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager |
List | pgsql-hackers |
On Wed, Mar 4, 2020 at 11:45 AM Mahendra Singh Thalor <mahi6run@gmail.com> wrote: > > On Mon, 24 Feb 2020 at 15:39, Amit Kapila <amit.kapila16@gmail.com> wrote: > > > > On Thu, Feb 20, 2020 at 8:06 AM Andres Freund <andres@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). > > b. Change lock.c so that group locking is not considered for these two > > lock types. For ex. in LockCheckConflicts, along with the check (if > > (proclock->groupLeader == MyProc && MyProc->lockGroupLeader == NULL)), > > we also check lock->tag and call it a conflict for these two locks. > > c. The deadlock detector can ignore checking these two types of locks > > because point (a) ensures that those won't lead to deadlock. One idea > > could be that FindLockCycleRecurseMember just ignores these two types > > of locks by checking the lock tag. > > Thanks Amit for summary. > > Based on above 3 points, here attaching 2 patches for review. > > 1. v01_0001-Conflict-EXTENTION-lock-in-group-member.patch (Patch by Dilip Kumar) > Basically this patch is for point b and c. > > 2. v01_0002-Added-assert-to-verify-that-we-never-try-to-take-any.patch > (Patch by me) > This patch is for point a. > > After applying both the patches, make check-world is passing. > > We are testing both the patches and will post results. > > Thoughts? +static void AssertAnyExtentionLockHeadByMe(void); +/* + * AssertAnyExtentionLockHeadByMe -- test whether any EXTENSION lock held by + * this backend. If any EXTENSION lock is hold by this backend, then assert + * will fail. To use this function, assert should be enabled. + */ +void AssertAnyExtentionLockHeadByMe() +{ Some minor observations on 0002. 1. static is missing in a function definition. 2. Function name should start in new line after function return type in function definition, as per pg guideline. +void AssertAnyExtentionLockHeadByMe() -> void AssertAnyExtentionLockHeadByMe() -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
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