<div dir="ltr"><div class="gmail_quote">On Fri, May 21, 2010 at 1:24 AM, Jan Wieck <span dir="ltr"><<a href="mailto:JanWieck@yahoo.com">JanWieck@yahoo.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<br>
In a multi node cluster, not every node necessarily needs to be able to<br>
talk to every other node. Let us just look at a cascaded 3 node cluster:<br>
<br>
1 - 2 - 3<br>
<br>
This setup requires 4 sl_path entries to work:<br>
<br>
server=1, client=2<br>
server=2, client=1<br>
server=2, client=3<br>
server=3, client=2<br>
<br>
And it is supposed to generate the following sl_listen rows:<br>
<br>
origin=1, receiver=2, provider=1<br>
origin=1, receiver=3, provider=2<br>
origin=2, receiver=1, provider=2<br>
origin=2, receiver=3, provider=2<br>
origin=3, receiver=1, provider=2<br>
origin=3, receiver=2, provider=3<br>
<br>
It does not matter which node is currently the origin of any set at all.<br>
All these paths and connections are important for the health and well<br>
being of the Slony cluster. If for example the listening for events from<br>
2, receiver=3 would be broken, then node 3 would still perfectly fine<br>
replicate data originating from 1. But as soon as you move set to node<br>
2, it would start falling behind and you effectively lose your second<br>
level backup.<br>
<br>
This is why Slony originally created a SYNC on EVERY node at least every<br>
10 seconds. Just so there is some harmless event passing going on to<br>
have something to monitor and keep sl_status looking good.<br>
<br>
That is what got removed and that is what I think we should put back.<br clear="all"><br></blockquote><div><br>This is exactly the kind of Slony black magic I want to understand. Do we have someplace where we can get these internals of Slony, or design specs; or would you suggest diving into code?<br>
<br>Regards,<br></div></div>-- <br>gurjeet.singh<br>@ EnterpriseDB - The Enterprise Postgres Company<br><a href="http://www.enterprisedb.com">http://www.enterprisedb.com</a><br><br>singh.gurjeet@{ gmail | yahoo }.com<br>
Twitter/Skype: singh_gurjeet<br>
<br>Mail sent from my BlackLaptop device<br>
</div>