Re: Centos 6.9 and centos 7

[Nicola Contu <nicola.contu@xxxxxxxxx>]

To make a better testing, I used a third server.

This is identical to the centos 7 machine, and it is not included in the replica cluster.

Nobody is accessing this machine, this is top :

top - 14:48:36 up 73 days, 17:39,  3 users,  load average: 0.00, 0.01, 0.05

Tasks: 686 total,   1 running, 685 sleeping,   0 stopped,   0 zombie

%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st

KiB Mem : 26383592+total,  1782196 free,  2731144 used, 25932257+buff/cache

KiB Swap: 16777212 total, 16298536 free,   478676 used. 21693456+avail Mem

These are timings :

Time: 2.841 ms

Time: 1.980 ms

Time: 2.240 ms

Time: 2.947 ms

Time: 2.828 ms

Time: 2.227 ms

Time: 1.998 ms

Time: 1.990 ms

Time: 2.643 ms

Time: 2.143 ms

Time: 2.919 ms

Time: 2.246 ms

I never got same results of the centos 6.9 machine.

2017-12-04 15:40 GMT+01:00 Nicola Contu <nicola.contu@xxxxxxxxx>:

These are the timings in centos 7 :

Time: 4.248 ms

Time: 2.983 ms

Time: 3.027 ms

Time: 3.298 ms

Time: 4.420 ms

Time: 2.599 ms

Time: 2.555 ms

Time: 3.008 ms

Time: 6.220 ms

Time: 4.275 ms

Time: 2.841 ms

Time: 3.699 ms

Time: 3.387 ms

These are the timings in centos 6:

Time: 1.722 ms

Time: 1.670 ms

Time: 1.843 ms

Time: 1.823 ms

Time: 1.723 ms

Time: 1.724 ms

Time: 1.747 ms

Time: 1.734 ms

Time: 1.764 ms

Time: 1.622 ms

This is top on centos 6 :

[root@****]# top

top - 14:33:32 up 577 days, 23:08,  1 user,  load average: 0.16, 0.11, 0.15

Tasks: 1119 total,   1 running, 1118 sleeping,   0 stopped,   0 zombie

Cpu(s):  0.0%us,  0.1%sy,  0.0%ni, 99.9%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st

Mem:  132040132k total, 129530504k used,  2509628k free,   108084k buffers

Swap: 11665404k total,   331404k used, 11334000k free, 124508916k cached

This is top on centos 7:

top - 14:35:38 up 73 days, 19:00,  6 users,  load average: 22.46, 20.89, 20.54

Tasks: 821 total,  13 running, 807 sleeping,   0 stopped,   1 zombie

%Cpu(s): 14.2 us,  5.0 sy,  0.0 ni, 77.5 id,  3.1 wa,  0.0 hi,  0.2 si,  0.0 st

KiB Mem : 26383592+total,  4301464 free,  6250384 used, 25328406+buff/cache

KiB Swap: 16777212 total, 11798876 free,  4978336 used. 24497036+avail Mem

The production machine is obviously more accessed. But that does not seem to be the problem as running the same query on the replica of the production machine (same config of the master but not accessed by anyone) gives the same bad result:

Time: 6.366 ms

2017-12-04 15:19 GMT+01:00 Chris Mair <chris@xxxxxxxx>:

centos 7 :
Time: 3.884 ms

centos 6.9

Time: 1.620 ms

Is there anything you can advice to solve or identify the problem?

Can you run this query 10 times on each server and note the timings?

I'd like to see the reproducability of this.

Also: both machines are otherwise idle (check with top or uptime)?

Bye,
Chris.