minimal update trigger

On Tue, Feb 19, 2008 at 09:32:30PM -0500, Andrew Dunstan wrote:

As discussed a little while back, I would like to add a generic
trigger function which will force an update to skip if the new and
old tuples are identical.

This one has lots of use cases. Did the earlier discussion settle on
whether there should be a GUC and/or CREATE DATABASE and/or initdb
option for this?

Cheers,
David.

The guts of this is the following snippet of code:

| rettuple = newtuple = trigdata->tg_newtuple;
oldtuple = trigdata->tg_trigtuple;

if (newtuple->t_len == oldtuple->t_len &&
newtuple->t_data->t_hoff == oldtuple->t_data->t_hoff &&
HeapTupleHeaderGetNatts(newtuple->t_data) == HeapTupleHeaderGetNatts(oldtuple->t_data) &&
(newtuple->t_data->t_infomask & ~HEAP_XACT_MASK) ==
(oldtuple->t_data->t_infomask & ~HEAP_XACT_MASK) &&
memcmp(((char *)newtuple->t_data) + offsetof(HeapTupleHeaderData, t_bits),
((char *)oldtuple->t_data) + offsetof(HeapTupleHeaderData, t_bits),
newtuple->t_len - offsetof(HeapTupleHeaderData, t_bits)) == 0)
{
rettuple = NULL;
}

return rettuple;

I propose to call the function pg_minimal_update.

Unless there is an objection I will put together a patch + docs for this shortly. Not quite sure what section of the docs to put it in - maybe a new subsection of the Functions chapter?

cheers

andrew
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David Fetter wrote:

On Tue, Feb 19, 2008 at 09:32:30PM -0500, Andrew Dunstan wrote:

As discussed a little while back, I would like to add a generic
trigger function which will force an update to skip if the new and
old tuples are identical.

This one has lots of use cases. Did the earlier discussion settle on
whether there should be a GUC and/or CREATE DATABASE and/or initdb
option for this?

None of the above. All we will be providing is a trigger function. You
would create the trigger as with any other trigger:

| CREATE TRIGGER _min BEFORE UPDATE ON mytable
FOR EACH ROW
EXECUTE PROCEDURE pg_minimal_update();

cheers

andrew
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