Re: Performance Improvement by reducing WAL for Update Operation

On Friday, January 11, 2013 11:09 PM Simon Riggs wrote:
On 11 January 2013 17:08, Amit kapila <amit.kapila@huawei.com> wrote:

>>> Just reviewing the patch now, making more sense with comments added.
>
>>>In heap_delta_encode() do we store which columns have changed?
>
>> Not the attribute bumberwise, but offsetwise it is stored.

> (Does that mean "numberwise"??)  Yes.

> Can we identify which columns have changed? i.e. 1st, 3rd and 12th columns? As per current algorithm, we can't as it
isbased on offsets. What I mean to say is that the basic idea to reconstruct tuple during recovery  is copy data from
oldtuple offset-wise (offsets stored in encoded tuple) and use new data (modified column data) from encoded tuple
directly.So we don't need exact column numbers. 

With Regards,
Amit Kapila.