21. 12. 2018.

How to quickly check disk(s) speed limit on Linux – part 3

This is the third part of a series of articles about measuring performance of disk subsystem. In the first part you can find details of how to measure disk performance by using dd command: https://www.josip-pojatina.com/en/how-to-quickly-check-disks-speed-limits-on-linux/ while in the second part you can find similar information by using the hdparm utility: https://www.josip-pojatina.com/en/how-to-quickly-check-disks-speed-limit-on-linux-part-2/ In this blog I’ll […]

14. 12. 2018.

How to quickly check disk(s) speed limit on Linux – part 2

In the previous part of disk speed series you can see one way to test disk speed by using special options of the dd command. In this article another utility – hdparm will be described. What is common with the previous way of testing HDD disk performance is in it’s simplicity, meaning you only need […]

04. 12. 2018.

How to quickly check disk(s) speed limit on Linux

Many times I can testify that IT professionals are talking about performance without even try the most simplistic tests to find out what are the HW capabilities/limits they have. One of the first things I usually do when facing with unknown environment is to run several tests to find out how much I can get […]

27. 09. 2018.

Non prefixed local index and slow SQL

Recently I’ve been asked to help explain why one query is running so slow based on only SQL text and table definition that is provided. As query was pretty big (several hundreds lines of code), at the first I thought that is mission impossible, as I have no explain plan available, no running stats, no […]

16. 08. 2018.

Exadata / Linux crash – capturing kernel dump on Linux systems

This article has been motivated from real life issue experienced on Exadata system running a few dozen of Oracle databases. I have already written about Exadata shortcoming in one of previous articles where I stressed that one of the main disadvantages of Exadata machine is non-existent virtualization technology. Oracle recognizes Oracle VM as the only […]

28. 07. 2018.

Supplemental logging – when to use it (and when not)

Supplemental logging feature along with streaming and CDC (change data capture) is available for a long time and is used mainly as one of the integration options especially for loading data from transactional (OLTP) into DW (Data Warehouse) staging tables. During my engagement on project for one large retailer, I noticed significant performance penalties due […]

08. 05. 2018.

Oracle tracing mechanism and when not to use it

Quite recently I had to trace/profile an extremely intensive batch job to provide information to Oracle for a further analysis. At very first moment it was obvious that this is a wrong approach and whatever we’ll get, it cannot server as evidence of performance issue that we have, as TKProf is designed to trace single […]

09. 04. 2018.

Resource Manager – internal plan

In this article I’m going to disclose Oracle Resource Manager Internal plan and how it can influence on database performances. Many of Oracle DBA are convinced that Resource Manager is not active, and that RM has to be enabled to be active. To confirm that theory, DBA can execute the following statement: select name, display_value, […]

26. 12. 2017.

Calling PL/SQL functions from the SQL and it’s influence on query execution

In all books that I red about performance tuning in Oracle (and other major vendor) relational databases, you can find that when optimizing SQL, you remove the select part and concentrate on part starting with FROM clause to inspect what tables have been involved along with the WHERE clause. Recently I have a interesting case […]

06. 09. 2017.

AWR migration between databases

This time I’ll explain AWR statistics migration between databases. This is not a new feature (available from 10g) but many DBA/Architects doesn’t know how to use it properly or even that this feature exist. Basically, the migration itself is very simple, and Oracle has provided scripts (awrextr.sql & awrload.sql) to make migartion as simple as […]