From: | Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, vignesh C <vignesh21(at)gmail(dot)com> |
Subject: | Re: making relfilenodes 56 bits |
Date: | 2022-08-01 05:20:59 |
Message-ID: | CAFiTN-vvQ6f0V6Y_-p1xpomEm+1ptt54A9K5LCX2TQarG=7P9Q@mail.gmail.com |
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On Sat, Jul 30, 2022 at 1:35 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> > On 2022-Jul-29, Robert Haas wrote:
> >> Yeah, if we think it's OK to pass around structs, then that seems like
> >> the right solution. Otherwise functions that take RelFileLocator
> >> should be changed to take const RelFileLocator * and we should adjust
> >> elsewhere accordingly.
>
> > We do that in other places. See get_object_address() for another
> > example. Now, I don't see *why* they do it.
>
> If it's a big struct then avoiding copying it is good; but RelFileLocator
> isn't that big.
>
> While researching that statement I did happen to notice that no one has
> bothered to update the comment immediately above struct RelFileLocator,
> and it is something that absolutely does require attention if there
> are plans to make RelFileNumber something other than 32 bits.
I think we need to update this comment in the patch where we are
making RelFileNumber 64 bits wide. But as such I do not see a problem
in using RelFileLocator directly as key because if we make
RelFileNumber 64 bits then its structure will already be 8 byte
aligned so there should not be any padding. However, if we use some
other structure as key which contain RelFileLocator i.e.
RelFileLocatorBackend then there will be a problem. So for handling
that issue while computing the key size (wherever we have
RelFileLocatorBackend as key) I have avoided the padding bytes in size
by introducing this new macro[1].
[1]
#define SizeOfRelFileLocatorBackend \
(offsetof(RelFileLocatorBackend, backend) + sizeof(BackendId))
--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com
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