Fixing SQL plans on ADG using SQL Profiles

With Active Dataguard setup, many of the read only applications runs on ADG and sometime the SQLs that are used by these applications runs into bad plans. ADG being a read only database, its not possible to create a baseline or a profile on ADG.

One of the way to have good plan for SQLs running on ADG is to make them run on primary first and fix the plan by creating profile or baseline (more...)

Using UDev to configure ASM disks

This is a small article on using UDev on RHEL 7. I have a virtual box with RHEL 7 and I am configuring ASM diskgroups.

Before we configure ASM diskgroups, we need to have disks/partitions available at OS level and those should be recognized by ASM. Oracle provides a utility called ASMLib which can be installed and used very easily to configure disk/partitions at OS level.

ASMLib stamps the header of partitions/disk at OS level (more...)

Oracle 12c Learning Series: Automatic Data Optimization – ADO

I am starting Oracle 12c learning series, where I am planning to publish multiple articles on Oracle 12c new features. I hope these articles will be helpful to DBAs aspiring for OCP 12c certification and also others who are planning to implement these features in there databases.

This is a very long post about ADO – Automatic Data Optimization, which is one of the ILM strategy to manage aging data. So please be patient while reading this article. This article provides end-to-end details (more...)

Previewing Backup Restore

Introduction:

This is a short article on RMAN where we can check if our backups are really intact and can help us in critical situation when we have to restore and recover the database.

We have a command option called PREVIEW which we can use with RESTORE DATABASE. This option does not actually restore the datafiles from backup but it just tell us SCN number until which we should be recovering our database. It also tells (more...)

Library Cache: Mutex X – Bug 20879889 – Fixed in 11.2.0.4

I recently encountered a bug related to MView log causing very high library cache: mutex x wait events.

I will brief about the debugging steps I tried and fix for the same.

Few things to note before I proceed:-

  • We observed huge wait events for library cache: mutex X whenever we performed flip to standby or when DB was bounced. I am implying that library cache was cold and didn’t had required cursor information and object handles.
  • Load on the (more...)

Mutex: What do we know ?

In my previous article on Latches, I mentioned various things related to latches including different types and their behavior.

In this article I will describe similar things about mutexes.

Mutex are low level serialization / locking mechanism to protect memory structure inside library cache.

Why there was a change from Latches ? 

Mutex was introduced from 10.2 onwards and have been proved very efficient in managing library cache operations.

Mutex takes less memory then latches. Typically latch (more...)

Latches: What do we know ?

Latches are low level serialization mechanism which protects memory areas inside SGA. They are light wait and less sophesticated than enqueues and can be acquired and released very quickly.

Latch acquisition does not involve any complex algorithm and is based on test-and-set atomic instruction of a computer processor.

Latch Classification:

Latch can be classified in multiple ways:-

Shared latch and exclusive latch:

Shared latch is the one which can be shared by multiple processes/sessions.

Example (more...)

Brief about Workload Management in Oracle RAC

This is a brief article about workload management in RAC. I tried to cover different components of workload management in RAC and how they are configured at client side or server side. I haven’t gone into details of configuration steps but just mentioned in brief about how it can be done.

Readers are advised to refer Oracle documentation to understand details about configuration of workload management.

Workload management on RAC

There are 2 major components (more...)

How many checkpoints in Oracle database ?

This Question came to my mind when I was discussing “direct path reads” with DBA candidates. I was surprised that many DBAs were not aware of object level checkpoint that happens while doing direct path read. So I thought many DBAs may not be knowing different level of checkpoints that happens in the database and hence the question.

Well, the answer is 7 (as per my knowledge). Oracle does 7 different checkpoints at various stages. Lets check out what (more...)

Coverting MySQL database character set to UTF8

Recently I was engaged to convert the character set for few MySQL databases from latin1 to UTF8 collation utf8_general_ci. This article describes the approach taken for doing the same.

First I will describe various levels at which we can change the character set and collation and then we will see how to convert existing data in a database to required character set.

Backup your database:

Before even thinking about changing character set for your database, (more...)