Re: [HACKERS] Pluggable storage

On Tue, Nov 14, 2017 at 4:12 PM, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> Hmm. Am I reading it right that this discussion led to moving
> essentially all code from tqual.c to heapam? Given the hard time we've
> had to get tqual.c right, it seems fundamentally misguided to me to
> require that every single storage AM reimplements all the visibility
> routines.
>
> I think that changing tqual's API (such as not passing HeapTuples
> anymore but some other more general representation) would be okay and
> should be sufficient, but this wholesale movement of code seems
> dangerous and wasteful in terms of future reimplementations that will be
> necessary.
>

I don't think the idea is to touch existing tqual.c in any significant
way. However, some other storage engine might need a different way to
check the visibility of tuples so we need provision for that. I think
for storage engine where tuple headers no longer contain transaction
information and or the old versions of tuples are chained in separate
storage (say undo storage), current visibility routines can be used.
I think the current tqual.c is quite tightly coupled with the
HeapTuple representation, so changing that or adding more code to it
for another storage engine with different tuple format won't be of
much use.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com