EBR – Part 7: Editioning Views

This is part 7 of a post series about EBR.

Visit the index page for all the parts of the series

Introduction

Our next use case is adding a column that represents a new logic to the PEOPLE table, and making the corresponding changes in the PEOPLE_DL and APP_MGR packages. Of course, as we speak about EBR, the upgrade from the previous version to the new one should be online.
An online upgrade means that (more...)

Filtering outliers from Oracle APEX activity logs

Last year I described a simple test case that described how to remove outliers from a fictional dataset using the STDDEV() analytical function .
http://www.grassroots-oracle.com/2017/06/removing-outliers-using-stddev.html

I want to follow this up with a practical case using one of my favourite data sets - the apex_workspace_activity_logs that record who opened what page, in what context, and how long it took to generate.

I've been keeping an eye on the performance of a particular page, (more...)

PostgreSQL Calling File

Somebody asked: How do you run a script file from PostgreSQL’s psql prompt? I created two files to answer the question. Here are the two files:

Static File

SELECT 'Hello World!';

Dynamic File

SELECT 'Hello ['||current_user||']!';

It’s a simple solution, you put a \i or \include before the script file name, like:

\i helloworld.sql

or

\include hellowhom.sql

I hope this helps those trying to call SQL script files from an interactive psql session.

The Performance of the FIRST and LAST Functions

Overview

One of the first posts I wrote in this blog (almost five years ago) was about the FIRST and LAST aggregate functions.
These functions are, in a way, extended versions of the much more popular aggregate functions MIN and MAX.
MIN and MAX allow you (conceptually) to sort a group of rows by some column and return the value of that column from the first or last row in the sorted group.
The FIRST (more...)

Beware (Sort-Of) Ambiguous Column Names In Sub-Selects

This morning I received an UPDATE statement from a developer that I was testing. It ran without errors but then I saw that it updated 5 rows when it should have only updated 3. The reason gave me a little shock so I whipped up a simple test-case to reproduce the problem.

First we create two tables:

CREATE TABLE foo (
    id int
    , name varchar(30)
);
CREATE TABLE
CREATE TABLE (more...)

EBR – Part 6: Editionable and Non-Editionable, Editioned and Non-Editioned

This is part 6 of a post series about EBR.
In part 1 we created the baseline model and code – a table (PEOPLE) and two packages (PEOPLE_DL and APP_MGR).
In part 2 we saw that even a simple change – a package body compilation – can be dangerous in a busy system.
In part 3 we learned about editions and how they can be used for solving the problems described in part 2, so (more...)

Excessive Locking when Dropping a Table in 11g

I tried to drop a table today and failed due to “ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired”.
That was weird because I knew that nobody had been using this table for months, and that the table had no enabled foreign keys.
A quick investigation revealed the cause – the DROP TABLE operation tried to lock another table (in the quite aggressive “Share” mode) that was referenced by a (more...)

A Single Query with Many Filter Combinations – Part 3

In a recent post I suggested a way to write a single SQL query that filters a table by one or more of several columns.
Here is the query from that post:

select * from employees where rowid in (
  select rid from (
    select rowid rid from employees where department_id = :department_id
    union all
    select rowid rid from employees where job_id = :job_id
    union all
    select rowid rid from employees where manager_id = :manager_id
     (more...)

A Single Query with Many Filter Combinations – Part 2

In the previous post I suggested a way to write a single SQL query that filters the EMPLOYEES table (as an example) by one or more of the following columns: DEPARTMENT_ID, JOB_ID, MANAGER_ID and LAST_NAME.

Here is the query from the previous post:

select * from employees where rowid in (
  select rid from (
    select rowid rid from employees where department_id = :department_id
    union all
    select rowid rid from employees where job_id  (more...)

A Single Query with Many Filter Combinations

Let’s assume the EMPLOYEES table (from the HR schema) contains many records, and we want to write an (efficient) SQL query that filters it by one or more of the following columns: DEPARTMENT_ID, JOB_ID, MANAGER_ID and LAST_NAME.
For example:

  • in one execution we may want to get all the employees with DEPARTMENT_ID = 80
  • in a second execution all the employees that their LAST_NAME is King
  • in a third execution all the employees (more...)

Adding a Datafile to Temp Tablespace

When monitoring Tablespace Usage (see my Tablespace Usage blog post for more info), there comes a point when you need to add a datafile to the temp tablespace to allow for growth and more importantly get below a monitoring threshold for example in OEM or OpsView.

Query to see Current Temp Datafiles State

To see the current state of the temp datafiles:

set pages 999
set lines 400
col FILE_NAME format a75
select d.TABLESPACE_NAME,  (more...)

Friday Philosophy – Explaining How Performance Tuning Is Not Magic?

Solving performance issues is not magic. Oh, I’m not saying it is always easy and I am not saying that you do not need both a lot of knowledge and also creativity. But it is not a dark art, at least not on Oracle systems where we have a wealth of tools and instrumentation to help us. But it can feel like that, especially when you lack experience of systematically solving performance issues.

SQL statement (more...)

Tool to Assist with Basic SQL Analysis

I just came back from RMOUG Training Days conference. It was my first time in Colorado (and obviously my first RMOUG training day) and it was really great (I wrote about it in another post). During my second session (From 4 Minutes to 8 Seconds – about a real SQL tuning case I had quite … Continue reading Tool to Assist with Basic SQL Analysis

SQL with Apache Spark, easy!

Reading about cluster computing developments like Apache Spark and SQL I decided to find out.

What I was after was to see how easy is to write SQL in Spark-SQL. In this micro-post I will show you how easy is to SQL a JSON file.

For my experiment I will use my chrome_history.json file which you can download from your chrome browser using the extension www.JSON-XLS.com. To run the SQL query on (more...)

Constraint Optimization Summary

This is the last part of a series about Constraint Optimization.
In this post I’ll summarize the conclusions from the previous parts.

When we add a constraint to an existing table, there are two aspects that are worth taking into consideration:

Duration

When the table contains a significant number of rows, adding a constraint may take a lot of time. In some cases Oracle applies a very nice optimization that can reduce this time to (more...)

Adding a Unique Constraint in an Online Way

Note: unlike most of my posts, this one assumes using Enterprise Edition

I have a table t and I want to add a unique constraint on one of its columns – c1.

The Offline Way

The straightforward and most simple way to do it is using a single alter table statement:

SQL> alter table t add constraint c1_uk unique (c1);

Table altered.

By default, Oracle creates in this operation a unique constraint (named c1_uk) and (more...)

SQL Magic Squares – or Why the Optimizer does not like Magic

A long-time player at the Oracle Dev Gym tried his hand at generating Magic Squares using SQL.



When he attempted to tune his statement a bit, he was surprised that it didn't go a little faster as expected, rather it went from 2 minutes to 45 minutes? At that point he contacted me to see if I could explain the mystery...



So thank you, Hamid Talebian, for the interesting case. It was fun to play (more...)

Ergänzungen zu coalesce und NVL

Vor längerer Zeit hatte ich hier gelegentlich auf Artikel verwiesen, die sich mit dem unterschiedlichen Verhalten von NVL und coalesce beschäftigten und einerseits auf die short-circuit evaluation mit coalesce und andererseits auf deren Ausklammerung im Fall von Sequencen hinwiesen. Jetzt haben die Herren Lewis und McDonald dazu ergänzende Beobachtungen geliefert.
  • Jonathan Lewis weist darauf hin, dass coalesce beim costing schlechter abschneidet als NVL, weil es mit dem Standardwert von 1% für Gleichheit operiert, der für (more...)

How to fix queries on DBA_FREE_SPACE that are slow

I found myself in a situation where OpsView a monitoring tool, was having difficulty monitoring the tablespaces for a particular pluggable database.

Upon investigation it was found the queries against the dictionary table DBA_FREE_SPACE were taking a very long time:

SQL> set timing on
SQL> select nvl(sum(dfs.bytes)/1024/1024,0) from dba_free_space dfs where dfs.tablespace_name = 'USERS';

NVL(SUM(DFS.BYTES)/1024/1024,0)
-------------------------------
 70.75

Elapsed: 00:00:10.98

There are 60 tablespaces in this pluggable database, which the time varied (more...)

Dynamic LOV with Pipeline function

A new year brought me some new tasks. I had to take over a generic Excel import and the customer wanted some extension by checking if the join on the master tables were successful.

Unfortunate we were talking about a generic solution which meant that all the configuration was saved inside tables including the LOV-tables which were saved as simple select statements.

Goal:
Show all import rows/values which were not fitting towards the master data.

(more...)