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March 2019

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

Cartesian Join

I wrote this note a little over 4 years ago (Jan 2015) but failed to publish it for some reason. I’ve just rediscovered it and it’s got a couple of details that are worth mentioning, so I’ve decided to go ahead and publish it now.

A recent [ed: 4 year old] question on the OTN SQL forum asked for help in “multiplying up” data – producing multiple rows from a single row source. This is something I’ve done fairly often when modelling a problem, for example by generating an orders table and then generating an order_lines table from the orders table, and there are a couple of traps to consider.

Less slamming V$SQL

It’s a holiday here today in Perth, so a very brief blog post because I’ve been busy doing other things today Smile

IMG_20190303_114220_012

Hash Optimisation-

Franck Pachot did an interesting presentation at the OBUG (Belgium user group) Tech Days showing how to use one of the O/S debug/trace tools to step through the function calls that Oracle made during different types of joins. This prompted me to ask him a question about a possible optimisation of hash joins as follows:

The hash join operation creates an in-memory hash table from the rowsource produced by its first child operation then probes the hash table with rows from the row source produced by the second child operation; but if there are no rows in the first row source then there’s no need to acquire rows from the second row source, so Oracle doesn’t call the second child operation.