On 20.06.2012 11:17, Simon Riggs wrote:
On 20 June 2012 15:45, Heikki Linnakangas
<heikki.linnakan...@enterprisedb.com> wrote:
On 20.06.2012 10:32, Simon Riggs wrote:
On 20 June 2012 14:40, Heikki Linnakangas
And I'm worried
it might not even be enough in more complicated scenarios.
It is not the only required conflict mechanism, and has never been
claimed to be so. It is simply one piece of information needed, at
various times.
So, if the origin id is not sufficient for some conflict resolution
mechanisms, what extra information do you need for those, and where do you
put it?
As explained elsewhere, wal_level = logical (or similar) would be used
to provide any additional logical information required.
Update and Delete WAL records already need to be different in that
mode, so additional info would be placed there, if there were any.
In the case of reflexive updates you raised, a typical response in
other DBMS would be to represent the query
UPDATE SET counter = counter + 1
by sending just the "+1" part, not the current value of counter, as
would be the case with the non-reflexive update
UPDATE SET counter = 1
Handling such things in Postgres would require some subtlety, which
would not be resolved in first release but is pretty certain not to
require any changes to the WAL record header as a way of resolving it.
Having already thought about it, I'd estimate that is a very long
discussion and not relevant to the OT, but if you wish to have it
here, I won't stop you.
Yeah, I'd like to hear briefly how you would handle that without any
further changes to the WAL record header.
Additional information required by logical information will be handled
by a new wal_level.
The discussion here is about adding origin_node_id *only*, which needs
to be added on each WAL record.
If that's all we can discuss here is, and all other options are off the
table, then I'll have to just outright object to this patch. Let's implement
what we can without the origin id, and revisit this later.
As explained, we can do nothing without the origin id. It is not
optional or avoidable in the way you've described.
It's only needed for multi-master replication, where the same table can
be updated from multiple nodes. Just leave that out for now. There's
plenty of functionality and issues left even without that.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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