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April 2017

Ask Jonathan

Oracle Scene, the magazine of the UK Oracle User Group is piloting a new regular feature called Ask Jonathan,  a chance to get an answer to any question you may have about how the Oracle database engine works.

I’m aiming to answer two or three questions per issue over the course of the year, using a format similar to the one Tom Kyte used in Oracle Magazine:  so if you have a question about the mechanisms, strategies, or mathematics of how Oracle does its thing then attach it as a comment to this posting.

Ideally the questions will have to be quite short (no 20MB trace files, massive schema definitions, or convoluted and exotic setup requirements or it will be too long), and I’ll aim to write something like half a page of in response.  I may summarise the question, or pick out the most interesting feature if it’s a bit too long to publish and answer in its entirety.

 

Parallel First_rows()

A recent posting on OTN raised the question of whether or not the “parallel” hint and the “first_rows(n)” hint were mutually incompatible. This reminded me that from time to time other posters on OTN (copying information from various websites, perhaps) have claimed that “parallel doesn’t work with first rows” or, conversely, “first rows doesn’t work with parallel”. This is one of those funny little myths that is so old that the script I’ve got to demonstrate the misconception is dated 2003 with a first test version of 8.1.7.4.

Since I haven’t run the test on any version of Oracle newer than 9.2.0.4 I thought it was time to dust it down, modernise it slightly, and run it again. So here’s the bit that creates a sample data set:

Completing JWT_NINjA for full JWT support

In the single blog post I wrote on the JWT_NINJA package back in June last year, I ended the post by saying that I needed to implement both a verify and a parse function for the package.

Well, it took me a year, but I finally had a reason to go and implement it. As I am getting into Oracle ORDS and trying to get some experience in building REST services, I want to be able to use JWT as the token generator for the application that I am building.

So a quick refresh on how to generate a token using the package:

Completing JWT_NINjA for full JWT support

In the single blog post I wrote on the JWT_NINJA package back in June last year, I ended the post by saying that I needed to implement both a verify and a parse function for the package.

Well, it took me a year, but I finally had a reason to go and implement it. As I am getting into Oracle ORDS and trying to get some experience in building REST services, I want to be able to use JWT as the token generator for the application that I am building.

So a quick refresh on how to generate a token using the package:

Service “696c6f76656d756c746974656e616e74″ has 1 instance(s).

Weird title, isn’t it? That was my reaction when I did my first ‘lsnrctl status’ in 12.2: weird service name… If you have installed 12.2 multitenant, then you have probably seen this strange service name registered in your listener. One per PDB. It is not a bug. It is an internal service used to connect to the remote PDB for features like Proxy PDB. This name is the GUID of the PDB which makes this service independent of the name or the physical location of the PDB. You can use it to connect to the PDB, but should not. It is an internal service name. But on a lab, let’s play with it.

CDB

I have two Container Databases on my system:

18:01:33 SQL> connect sys/oracle@//localhost/CDB2 as sysdba
Connected.
18:01:33 SQL> show pdbs
 
CON_ID CON_NAME OPEN MODE RESTRICTED
------ -------- ---- ---- ----------
2 PDB$SEED READ ONLY NO

Take a random REST

I needed to test ORDS for some webservice related projects at work. So I decided to build a rest interface for all the different random data functions in the RANDOM_NINJA package to test out, just how easy it is.

First order is to setup ORDS. Like always Tim over at oracle-base have a couple of really good articles on installing and setting up ORDS itself. So no need for me to duplicate that.

Take a random REST

I needed to test ORDS for some webservice related projects at work. So I decided to build a rest interface for all the different random data functions in the RANDOM_NINJA package to test out, just how easy it is.

First order is to setup ORDS. Like always Tim over at oracle-base have a couple of really good articles on installing and setting up ORDS itself. So no need for me to duplicate that.

Apex Interactive Grid and IOT’s

I love the interactive grid in Application Express.  And here’s why… (Warning: Ranting mode is now on Smile)

You can tell people

12cR2 DML monitoring and Statistics Advisor

Monitoring DML to get an idea of the activity on our tables is not new. The number of insert/delete/update/truncate since last stats gathering is tracked automatically. The statistics gathering job use it to list and prioritize tables that need fresh statistics. This is for slow changes on tables. In 12.2 we have the statistics advisor that goes further, with a rule that detects volatile tables:

SQL> select * from V$STATS_ADVISOR_RULES where rule_id=14;
 
RULE_ID NAME RULE_TYPE DESCRIPTION CON_ID
------- ---- --------- ----------- ------
14 LockVolatileTable OBJECT Statistics for objects with volatile data should be locked 0

But to detect volatile tables, you need to track DML frequency with finer grain. Let’s investigate what is new here in 12.2

MOS plugin

Few days back I was (again) angry at My Oracle Support “The page has expired” message appearing in an open tab I left for some time. I tried to find out how to avoid it, and it was relatively easy to do even though I don’t know JavaScript. Then I tried to make a plugin out of it so I it can be on by default & won’t need my attention.
Here it is: plugin for Chrome. It took me 2 seconds to come up with a name – MOS-cow and about 3 hours to prepare plugin.