Re: Global Sequences

On 16 October 2012 13:54, Peter Eisentraut <peter_e@gmx.net> wrote:
> On 10/15/12 5:33 PM, Simon Riggs wrote:
>> There are a few options
>> 1) Manual separation of the value space, so that N1 has 50% of
>> possible values and N2 has 50%. That has problems when we reconfigure
>> the cluster, and requires complex manual reallocation of values. So it
>> starts good but ends badly.
>> 2) Automatic separation of the value space. This could mimic the
>> manual operation, so it does everything for you - but thats just
>> making a bad idea automatic
>> 3) Lazy allocation from the value space. When a node is close to
>> running out of values, it requests a new allocation and coordinates
>> with all nodes to confirm the new allocation is good.
>
> What would the allocation service look like?  Is it another PostgreSQL
> server?  What's the communication protocol?  How would backups work?
> Crash recovery?

I've proposed a plugin for the allocation only. So the allocation
looks like anything you want.

Crash recovery and backups would not need changes.

> Option 4 is of course to use UUIDs.

That is a user level option. If user chooses sequences, then we must
support them.

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