Reduce Exadata Core Count

Ok, so I was preparing for a DC services migration with a client and this would involve resizing the CPU count of Exadatas for better attending those services. This way, one of the steps will require reduce CPU counts in one of the sites to be aligned with the license terms.

Checking for the steps to accomplish that, I found references to change CPU and core count, but always described in the case of increasing allocation. As per 2.7 Increasing the Number of Active Cores on Database Servers. But not so much about reducing, as this seems to be unusual…

Also considering that the planned change would be within the minimum number requirement: 2.1 Restrictions for Capacity-On-Demand on Oracle Exadata Database Machine.

Reviewing on MOS, we found the When Attempting to Change the Number of Cores, Errors With: DBM-10004 – Decreasing the Number of Active Cores is not Supported ( Doc ID 2177634.1 ), pointing to use the clause “FORCE” on “ALTER DBSERVER pendingCoreCount =x” command.

And this worked. I just disabled the iaasMode to play safe. Have a look:

[root@grepora01~]# dbmcli
DBMCLI: Release  - Production on Mon Jan 05 01:10:12 EEST 2019
Copyright (c) 2007, 2014, Oracle.  All rights reserved.
DBMCLI> LIST DBSERVER attributes coreCount
	 36/44
DBMCLI> ALTER DBSERVER pendingCoreCount = 24 force
DBM-10022: At least 26 physical cores need to be active in order to support IaaS.
DBMCLI> ALTER DBSERVER iaasMode = "off"
DBServer exadb01 successfully altered
DBMCLI> ALTER DBSERVER pendingCoreCount = 24 force
DBServer grepora01 successfully altered. Please reboot the system to make the new pendingCoreCount effective.
DBMCLI> LIST DBSERVER attributes pendingCoreCount
24/44

–> Restart the server
After restarting, it should look like:

DBMCLI> LIST DBSERVER attributes coreCount
	 24/44
DBMCLI> LIST DBSERVER attributes pendingCoreCount

Hope this helps!

ORA-07445: exception encountered: core dump [nstimexp()+45] [SIGSEGV] [ADDR:0x58] [PC:0x7F42ABB] [Address not mapped to object] []

Hello all,
I had faced some occourrences of this error in a 11.2.0.1 database recently.

ORA-07445: exception encountered: core dump [nstimexp()+45] [SIGSEGV] [ADDR:0x58] [PC:0x7F42ABB] [Address not mapped to object] []

After some investigation I found a match to Bug 3934729.
This issue is originally to matched to Bug 6918493, that is a reintroduction of Bug 2752985 but it’s fixed in 11.2.0.1.
However, on upgrading to 11.2.0.1 it’s a hit on Bug 3934729 which is fixed in 11.2.0.2.

Recommended actions are:
– Upgrade databases do 11.2.0.2 or higher. (best solution, but may require more efforts to validate the upgrade).
– Apply Patch 3934729: RANDOM ORA-07445 CORE DUMPS FROM DATABASE AND ORA-3113 FROM APPLICATION
– Set sqlnet.expire_time=0 (workaround)
– Ignore error.

After some research I decided to apply workaround, based on recommended usage of sqlnet.expire_time (Next weeks post is about this parameter :)).
This might be the root cause for the ORA-03135: connection lost contact and the actual value of this parameter on environment was 1, which is a very low value.

So, check which action is more suitable for your environment!
Hope it helps 🙂

Below some additional informations on my situation:

Continue reading

RHEL: Figuring out CPUs, Cores and Hyper-Threading

Hi all!
It’s a recurrent subject, right? But no one is 100% sure to how figure this out… So, let me quickly show you my way:

– Physical CPUs (sockets):

[root@mysrvr ~]# grep -i "physical id" /proc/cpuinfo | sort -u | wc -l
2
[root@mysrvr ~]# dmidecode -t processor |grep CPU
        Version: Intel(R) Xeon(R) CPU X5570 @ 2.93GHz
        Version: Intel(R) Xeon(R) CPU X5570 @ 2.93GHz

So, 2 physical CPUs.

– Physical Cores

[root@mysrvr ~]# egrep -e "core id" -e ^physical /proc/cpuinfo|xargs -l2 echo|sort -u
physical id : 0 core id : 0
physical id : 0 core id : 1
physical id : 0 core id : 2
physical id : 0 core id : 3
physical id : 1 core id : 0
physical id : 1 core id : 1
physical id : 1 core id : 2
physical id : 1 core id : 3

Each one of Physical Processors has 4 cores.
So, there is two quad-cores. This way, we have 8 cores at all.

– Logical CPUs

[root@mysrvr ~]# grep -i "processor" /proc/cpuinfo | sort -u | wc -l
16

Ok, so we have cores in double.
This means we have Hyper-Threading (technology by Intel Processors).

Not so hard, right?

Those links are similar and quite cool to understand the concepts:
https://access.redhat.com/discussions/480953
https://www.redhat.com/archives/redhat-list/2011-August/msg00009.html
http://www.intel.com/content/www/us/en/architecture-and-technology/hyper-threading/hyper-threading-technology.html

Matheus.