Re: Expanding the use of FLEXIBLE_ARRAY_MEMBER for declarations like foo[1]

On 2015-02-18 21:00:43 -0500, Tom Lane wrote:
> Michael Paquier <michael(dot)paquier(at)gmail(dot)com> writes:
> > 3) heapam.c in three places with HeapTupleHeaderData:
> > struct
> > {
> > HeapTupleHeaderData hdr;
> > char data[MaxHeapTupleSize];
> > } tbuf;
>
> And this, though I'm not sure if we'd have to change the size of the
> padding data[] member.

I don't think so.
/*
* MaxHeapTupleSize is the maximum allowed size of a heap tuple, including
* header and MAXALIGN alignment padding. Basically it's BLCKSZ minus the
* other stuff that has to be on a disk page. Since heap pages use no
* "special space", there's no deduction for that.
...
#define MaxHeapTupleSize (BLCKSZ - MAXALIGN(SizeOfPageHeaderData + sizeof(ItemIdData)))

> > 5) reorderbuffer.h with its use of HeapTupleHeaderData:
>
> Hmm. Andres will have to answer for that one ;-)

That should be fairly uncomplicated to replace.
...
/* tuple, stored sequentially */
HeapTupleData tuple;
HeapTupleHeaderData header;
char data[MaxHeapTupleSize];

probably can just be replaced by a union of data and header part - as
quoted above MaxHeapTupleSize actually contains space for the
header. It's a bit annoying because potentially some output plugin might
reference .header - but they can just be changed to reference
tuple.t_data instead.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services