Wrong Results with IOT, Added Column and Secondary Index

I found a “wrong results” bug yesterday, easily reproduced in 11g, 12c and 18c.

In short, we may get wrong results under the following circumstances:

  • We have an Index-Organized Table (IOT) with multi-column primary key, populated with rows
  • The table has a secondary index on part of the primary key columns
  • We add another column to the existing IOT
  • We select from the IOT while accessing it via the secondary index

Following is a simple (more...)

EBR – Part 9: Adding a New Column

This is part 9 of a post series about Oracle Edition-Based Redefinition.

Visit the index page for all the parts of the series

Introduction

In part 7 (“Editioning Views”) I introduced our third development use case – adding a new column that represents a new business logic.

I emphasize the fact it’s a new business logic, because sometimes we add new columns that come instead of existing columns, for replacing an existing business logic. (more...)

EBR – Part 8: The Last Planned Downtime

This is part 8 of a post series about Oracle Edition-Based Redefinition.

Visit the index page for all the parts of the series

Introduction

I concluded the previous post by stating that the application code should never reference tables directly; instead, every table should be covered by an editioning view and the application code should reference the views.

Starting from Scratch?

If you start developing a new system from scratch, I strongly recommend to follow (more...)

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...)

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...)

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...)

COLLECT INTO inside a Cursor Definition?

I have been programming in PL/SQL since 1993, more or less continuously (I’ve just realized that it’s exactly half of my life until now), so I know the PL/SQL syntax quite well.
So when I saw the following piece of code a few days ago, I was willing to bet it would not compile:

declare
    v_number_array sys.odcinumberlist;
begin
    for v_rec in (select rownum as num
                  bulk   collect
                  into   v_number_array
                  from   dual
                  connect by level < = 5)
    loop
        dbms_output.put_line(v_rec.num);
    end loop;
end;

(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...)