Re: [PATCH] Refactoring of LWLock tranches

On Tue, Feb 9, 2016 at 7:53 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Fri, Feb 5, 2016 at 3:17 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I think we ought to move the buffer mapping, lock manager, and
>> predicate lock manager locks into their own tranches also, perhaps
>> using this new named-tranche facility.
>
> Makes sense and attached patch implements it using new named
> tranches facility. One thing to note is that to make it work on
> EXEC_BACKEND builds, I have passed the individual LWLock
> array via save-restore backendparams mechanism. Now instead
> we could have initialised the LWLock arrays in each backend at
> start-up and I have tried to analyse that way as well, but we need
> to use NamedLWLockTrancheArray instead of
> NamedLWLockTrancheRequestArray in GetNamedLWLockTranche()
> and not only that, we also need to store number of locks
> information in NamedLWLockTrancheArray as well. So it seems
> it is better to use save-restore backendparams mechanism for
> passing LWLock arrays.

I'm not very keen on the way this puts RequestNamedTranches() into
miscinit.c. That doesn't really seem like it goes there, and I feel
like each subsystem should be responsible for requesting its own named
tranche rather than having it be centralized like this.

I think it might be helpful to split this into two patches. The first
would remove LWLockAssign() and NumLWLocks() and related bits, and
would use NUM_FIXED_LWLOCKS any place we currently call NumLWLocks().
The second would add the named tranches for the three kinds of locks
included in NUM_FIXED_LWLOCKS and then replace NUM_FIXED_LWLOCKS with
NUM_INDIVIDUAL_LWLOCKS.

--
Robert Haas
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