Re: non-HOT update not looking at FSM for large tuple update

On Thu, Mar 11, 2021 at 9:46 AM Matthias van de Meent <
boekewurm+postgres@gmail.com> wrote:

> Regarding the 2% slack logic, could we change it to use increments of
> line pointers instead? That makes it more clear what problem this
> solution is trying to work around; that is to say line pointers not
> (all) being truncated away. The currently subtracted value accounts

That makes sense.

> ...
> - if (len + saveFreeSpace > MaxHeapTupleSize)
> + if (len + saveFreeSpace > maxPaddedFsmRequest)
> ...
> - targetFreeSpace = Max(len, MaxHeapTupleSize - (MaxHeapTupleSize * 2 /
100));
> + targetFreeSpace = Max(len, maxPaddedFsmRequest);
> ...

If we have that convenient constant, it seems equivalent (I think) and a
bit more clear to write it this way, but I'm not wedded to it:

if (len + saveFreeSpace > MaxHeapTupleSize &&
    len <= maxPaddedFsmRequest)
{
    ...
    targetFreeSpace = maxPaddedFsmRequest;
}
else
    targetFreeSpace = len + saveFreeSpace;

Also, should I write a regression test for it? The test case is already
available, just no obvious place to put it.

--
John Naylor
EDB: http://www.enterprisedb.com