<html><body>
<br />
<br />
<table width="800" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td colspan="8" valign="top"><table width="800" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td colspan="8" valign="top"><table width="800" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td width="40" rowspan="2" valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td><IMG border="0" src="cid:118072611430900941@uk-mta-31.uk.mimecast.lan" ></td></tr></table></td>
<td width="9" rowspan="2"> </td>
<td width="480" valign="top" cellpadding="0" cellspacing="0">
<span style="font-size: 20px; font-weight: bold; font-family: Arial; margin: 0; padding: 0;">Piotr Gbyliczek</span>
<hr style="height: 0; border-top-style: solid; border-top-color: #E05206; color: #E05206; margin: 4px 0px; border-width: 1px 0 0;" />
<span style="font-weight: lighter; font-size: 14px; font-family: Arial; margin: 0; padding: 0;">Solutions Engineer</span>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tbody>
<tr><td height="4" style="font-size: 4px;" cellpadding="0" cellspacing="0"> </td></tr>
<tr>
<td width="56%" valign="top">
<span style="font-size: 11px; font-family: Arial; margin: 0; padding: 0;">
ddi. <strong>08454 210444</strong><br />
t. <strong>0845 123 2222</strong>
<br />e. <strong style="color:#303a3d; text-decoration:none;">P.Gbyliczek@node4.co.uk</strong></span>
</td>
<td width="44%" align="left" valign="top"><span style="font-size: 11px; font-family: Arial; margin: 0; padding: 0;"><strong>Nottingham Office</strong><br />Node4 Ltd, The POD,<br />10 Bottle Ln, Nottingham, NG1 2HL</span></td>
</tr>
</tbody>
</table>
<p> </p>
</td>
<td colspan="8" align="right" valign="top">
<table border="0" cellspacing="0" cellpadding="0"><tr><td><a href="http://www.node4.co.uk"><IMG border="0" alt="Visit www.node4.co.uk" src="cid:118072611430901141@uk-mta-31.uk.mimecast.lan" ></A></td></tr></table>
<table width="100%" height="46" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td colspan="8" height="12" style="font-size: 4px;" cellpadding="0" cellspacing="0"></td>
</tr>
<tr>
<td> </td>
<td align="right"><table border="0" cellspacing="0" cellpadding="0"><tr><td><a href="http://www.node4.co.uk"><IMG border="0" alt="Visit www.node4.co.uk" src="cid:118072611430901441@uk-mta-31.uk.mimecast.lan" ></A></td></tr></table></td>
<td> </td>
<td align="right"><table border="0" cellspacing="0" cellpadding="0"><tr><td><a href="http://www.twitter.co.uk/Node4Ltd"><IMG border="0" alt="Visit Node4 on Twitter" src="cid:118072611430901241@uk-mta-31.uk.mimecast.lan" ></A></td></tr></table></td>
<td> </td>
<td align="right"><table border="0" cellspacing="0" cellpadding="0"><tr><td><a href="https://www.linkedin.com/company/node4-ltd"><IMG border="0" alt="Visit Node4 on Linkedin" src="cid:118072611430901341@uk-mta-31.uk.mimecast.lan" ></A></td></tr></table></td>
<td> </td>
<td align="right"><table border="0" cellspacing="0" cellpadding="0"><tr><td><a href="http://www.facebook.com/Node4"><IMG border="0" alt="Visit Node4 on Facebook" src="cid:118072611430901041@uk-mta-31.uk.mimecast.lan" ></A></td></tr></table></td>
</tr>
</tbody>
</table>
<p> </p>
</td>
<td width="10" rowspan="2"> </td>
<td width="40" rowspan="2" valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td><IMG border="0" src="cid:118072611430900941@uk-mta-31.uk.mimecast.lan" ></td></tr></table></td>
</tr>
</tbody>
</table></td>
</tr>
</tbody>
</table>
<table width="800" border="0" cellpadding="0" cellspacing="0">
<tbody><tr>
<td>
<table border="0" cellspacing="0" cellpadding="0"><tr><td><a href="http://info.node4.co.uk/cloud-transformation-consultancy-services-0"><IMG border="0" src="cid:118072611430901541@uk-mta-31.uk.mimecast.lan" ></A></td></tr></table></td><td>
<table border="0" cellspacing="0" cellpadding="0"><tr><td><a href="http://info.node4.co.uk/mid-market-it-priorities-in-2018"><IMG border="0" src="cid:118072611430900841@uk-mta-31.uk.mimecast.lan" ></A></td></tr></table>
</td>
</tr>
</tbody></table>
<p> </p>
</td>
</tr>
<tr>
<td colspan="8">
On Tuesday, 24 July 2018 13:05:07 BST Muhammad Usama wrote:<BR>
<BR>
Hi Muhammad,<BR>
<BR>
> trusted_servers config could be used to mitigate the split-brain syndrome<BR>
> in older versions of Pgpool-II but<BR>
> if you are on 3.6.7 which has the quorum aware watchdog system you don't<BR>
> require to use trusted_servers config<BR>
> and leave it empty, of course if you don't have some other specific<BR>
> requirements as the one I described in above example.<BR>
> <BR>
> Please let me know if you need further clarification or explanation.<BR>
<BR>
Would that work in cluster with 2 pgpool nodes ? I'm guessing not, as "quorum" <BR>
suggests 3+ servers to be effective in my mind. However after your explanation <BR>
it seems to me that pgpool does not behave logically in regards to <BR>
"trusted_servers" and introduces some risks by this. <BR>
<BR>
I mean, why would any pgpool process stop itself due to failure to communicate <BR>
the trusted servers when there is communication with peer over the watchdog <BR>
channel ? I understand your hypothetical environment, and indeed, we don't <BR>
want to have application/clients connecting to the database via multiple <BR>
routes due to delegate IP being up on more than one pgpool server after <BR>
network partition. <BR>
<BR>
But that suggest the communication between nodes is severed, and ping to <BR>
trusted servers helps establish if given pgpool still has access to network, <BR>
in which case it is plausible that it is expected to have VIP on itself. In <BR>
case that it can't ping outside, there is even no point of bringing up the <BR>
VIP, as there is network issue and little expectation of traffic from app/<BR>
clients will get to it. <BR>
<BR>
Thinking of it, does this opens us up for a case where network partition runs <BR>
between pgpool nodes, and outside connectivity is not affected ? Both nodes <BR>
will bring up VIP then, and potentially make a bit of mess..<BR>
<BR>
Anyway, in case that watchdog is communicating fine with other nodes, but <BR>
trusted servers can't be contacted, watchdog should take priority, and dictate <BR>
that nothing should be done, imho. <BR>
<BR>
I think that it may be an edge case, and solution for that would be to get <BR>
another pgpool node running. is there a way to make a witness node in pgpool ? <BR>
I'm unable to add third pgpool node due to cost, but could install pgpool to <BR>
another server to make it 3 nodes. However, that server would be unable to <BR>
take production traffic, so should be never able to bring up VIP.<BR>
<BR>
Regards,<BR>
Piotr<BR>
<BR>
-- <BR>
<small style="font-family: Arial; color: #8E908F;">
<br />Node4 Limited is registered in England No: 04759927 and has its registered office at Millennium Way, Pride Park, Derby, DE24 8HZ<br />
The information contained in this email is confidential and is intended for the exclusive use of the email addressee shown.<br />
If you are not the addressee, any disclosure, reproduction, distribution or other dissemination or use of this communication is strictly prohibited.<br />
If you have received this mail in error, please notify our mail manager at <a href="mailto:abuse@node4.co.uk" style="color: #E05206; text-decoration: none;" target="_blank">abuse@node4.co.uk</a> and delete it from your system.<br />
Opinions expressed in this email are those of the individual not the company, unless specifically indicated to that effect.
<hr style="height: 0; border-top-style: solid; border-top-color: #D1D4D3; margin: 4px 0px; border-width: 1px 0 0;" />
This email has been scanned by Node4's Email Security System.
<hr style="height: 0; border-top-style: solid; border-top-color: #D1D4D3; margin: 4px 0px; border-width: 1px 0 0;" />
This email message has been delivered safely and archived online by Mimecast.</small>
</td>
</tr>
</tbody>
</table>
</body></html>