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March 2019

Tutorial: Troubleshooting Linux SSH Login Delay - Why does logging in always take 10 seconds?

As I’m delivering my Linux Troubleshooting training in a couple of months, I am going to blog about some typical issues and techniques we’ll troubleshoot in the class too.
I’ll start from a relatively simple problem - logging in to a server via SSH always takes 10 seconds. The delay seems to be pretty constant, there don’t seem to be major network problems and the server is not overloaded. Yet, remote logins always take 10 seconds.

Tutorial: Troubleshooting Linux SSH Login Delay - Why does logging in always take 10 seconds?

As I’m delivering my Linux Troubleshooting training in a couple of months, I am going to blog about some typical issues and techniques we’ll troubleshoot in the class too.
I’ll start from a relatively simple problem - logging in to a server via SSH always takes 10 seconds. The delay seems to be pretty constant, there don’t seem to be major network problems and the server is not overloaded. Yet, remote logins always take 10 seconds.

Oracle Security Training in London with Oracle University

I have just agreed some training dates with Oracle University in London and I will be teaching my very popular two day class How to Perform a security audit of an Oracle database on the 29th and 30th April 2019....[Read More]

Posted by Pete On 07/03/19 At 12:15 PM

Connections with a wallet – redux

Wow…it is nearly 4 years ago now that I wrote an article on connecting to the database via a wallet to avoid having to hard code passwords into script. That article is here:

https://connor-mcdonald.com/2015/09/21/connection-shortcuts-with-a-wallet/

So I went to do a similar exercise on my new 18c Windows database today, and to my surprise things went pear shaped at the very first step

Oracle 19c Data Guard sandbox created by DBCA -createDuplicateDB

Here are the commands I use to create a sandbox on Linux with a CDB1 database in a Data Guard configuration. I use the latest (19c) DBCA features to create the Primary and duplicate to the Standby.

I’m doing all in a VM which is a Compute Instance provisioned in the Oracle Cloud. In this example, I have an Oracle Linux 7.6 VM.DenseIO2.24 shape with 320GB RAM and 24 cores but remember that you will not be able to scale up/down so choose according to your credits...

I have 40GB in the / filesystem

OS and filesystem installation

I’ve installed the prerequisites as root (preinstall package, sudo and HugePages — here 200GB out of the 314GB I have):

19c Observe-Only Data Guard FSFO: no split-brain risk in manual failover

Fast-Start Failover (FSFO) is an amazing feature of Oracle Data Guard Broker which brings High Availability (HA)features in addition to the Disaster Recovery (DR) one.

Data Guard as an HA solution

By default, a physical standby database protects from Disaster Recovery (like when your Data Center is on fire or underwater, or with a power cut,…). But it requires a manual action to do the failover. Then, even if the failover is quick (seconds to minutes) and there’s no loss of data (if in SYNC), it cannot be considered as HA because of the manual decision which can take hours. The idea of the manual decision is to understand the cause as it may be better to just wait in case of a transient failure. Especially if the standby site is less powerful and application performance will be degraded.

12c Snapshots

I published a note a few years ago about using the 12c “with function” mechanism for writing simple SQL statements to takes deltas of dynamic performance views. The example I supplied was for v$event_histogram but I’ve just been prompted by a question on ODC to supply a couple more – v$session_event and v$sesstat (joined to v$statname) so that you can use one session to get an idea of the work done and time spent by another session – the first script reports wait time:

Getting locale warnings when logging on to Linux

This blogpost is about the reason and solving getting the following message, or messages alike these when logging i to a linux box using ssh:

-bash: warning: setlocale: LC_CTYPE: cannot change locale (UTF-8): No such file or directory

However, this is a warning. Please mind such an issue might be come up in another way, which can be more disrupting; at least in the past I had issues running perl for the same issue:

[root@dmcel01 ~]# /usr/local/bin/ipconf -verify
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = "en_US.UTF-8",
LC_ALL = "UTF-8",
LC_CTYPE = "UTF-8",
LANG = "en_US.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

Disabled EZCONNECT

Just a normal start to the day today…I had my coffee

coffee_gif

and then started working on some AskTOM questions. Naturally pretty much the first thing I needed to do is connect to my database, and then this happened:

My next Conferences in 2019

In my 2019 talks, a lot of performance stuff for DBA and Developers:

This year started with the amazing OBUG Belgium Tech Days 2019

The co-location of data and code, in present and future (like the MLE engine running JavaScript or Python in the database)

The most relevant statistics gathering in the 12.2 database (from 12cR2, 18c, 19c)

A different view on Join Methods by tracing the internal functions.

The Riga Dev Days in Latvia:

Riga Dev Days | Tech conference and the annual meeting point for developers in Baltic States.

Where I talk about microservices, and data/code co-location