Re: Composite Datums containing toasted fields are a bad idea(?)

On Mon, Apr 21, 2014 at 10:40 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2014-04-21 11:30:57 -0400, Tom Lane wrote:
>> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
>> > I unfortunately haven't followed this in detail, but shouldn't it be
>> > relatively easily to make this even cheaper by checking for
>> > HEAP_HASEXTERNAL? If it's not set we don't need to iterate over the
>> > composite's columns, right?
>>
>> That's the point I made further down:
>
> Oh, sorry. I started reading this thread from the end just now.
>
>> we could do that if we were willing
>> to abandon the principle that nested fields shouldn't be compressed.
>> It's not very clear what it'd cost us to give that up.
>
> I don't think the cost of that would be all that high.

I think it's pretty reasonable too.

> And too bad that infomask bits are so scarce :(. We really need to
> reclaim HEAP_MOVED_OFF and HEAP_MOVED_IN.

The only consequence of that is losing support for in-place update for
pre-9.0 (of which the only supported version is 8.4). I figure it's
also pretty reasonable to drop support for IPU for out of support
versions for new versions going forward. That would recover the bits
and yield some nice cleanups in tqual.c.

8.4 is scheduled to go out of support in July, so if you agree with my
reasoning 9.4 would be a candidate for not honoring 8.4 upgrade
support.

merlin