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So we are running Xen server 7.1  We have a MySQL server running Ubuntu 16.0.4 and another Ubuntu server 16.0.4 running Apache and PHP.  I have installed iperf for testing the speed and on average from the Apache server to the MySQL the speeds are 3.5Gbit/s.  Now from the MySQL server to the Apache server we are getting an average of 5.5Gbit/s. Why the huge difference?

 

We are working on upgrading and we now have a test MySQL server running on Ubuntu 18.0.4 and another Apache server also running on Ubuntu 18.04.  The average from Apache to MySQL is 3.6Gbit/s.  The average speed from MySQL to Apache is 3.7Gbit/s.  I'm having trouble understanding why the  speed difference both ways and why the old MySQL running on 16.0.4 to Apache server is 5.5Gbit/s but the newer MySQL server to the newer Apache server is only seeing 3.7Gbit/s.

All servers are on the same xen server, exact specs, same vlan, all servers are running as PV.

 

Any help or other ways to compare speeds and that is greatly appreciated.

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Well that is the odd thing.  The MYSQL server 16.0.4 doesn't have the xen tools installed.  Xen tools are installed on the other servers.  I did uninstall xen tools on the MySQL 18.0.4 to see if there would be a speed difference and it helped a little but not a whole lot.

 

Also, Ubuntu 18.0.4 was switching to netplan for configuring interfaces and that, I switched that back to using /etc/network/interfaces and that gave us more speed as well but i still am at a loss on why the old MySQL server is still so much fast and why it is just one way.  If anyone has any other way to troubleshoot this I'm all ears.  We are also noticing about a 3 second difference on our queries from the old server to the new and I do believe it has something to do with the network.

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According to this page https://docs.citrix.com/en-us/xenserver/7-1/system-requirements/guest-os-support.html

it shows that 18.0.4 should be supported.   Now this does say for xenserver 7.1 LTSR and my xen server shows 7.1.0-137272c so i would think it is supported.  It also does mention HVM but I do have it running has PV.

 

I did add these to the sysctl.conf and got better speed (average of 4.7 or 4.8 which is closer) I just can't tell if it is a xen server issue or an ubuntu os issue and not sure how to tell.

net.core.default_qdisc=fq
net.ipv4.tcp_congestion_control=bbr

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We are using 10GB NICs I can't remember the model of hand but will look that up.  For the Storage they are connecting to our NetApp SAN over iSCSI.  You mentioned that you substantially up the TCP buffer sizes.  Do you make those changes on the Xen hosts or the VM's and how do you do that?

 

Tobias, thanks for helping us troubleshoot this issue with us.

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