12c Parallel Execution New Features: Hybrid Hash Distribution – Part 2

In the second part of this post (go to part 1) I want to focus on the hybrid distribution for skewed join expressions.

2. Hybrid Distribution For Skewed Join Expressions

The HYBRID HASH distribution allows to some degree addressing data distribution skew in case of HASH distributions, which I've described in detail already in the past. A summary post that links to all other relevant articles regarding Parallel Execution Skew can be found here (more...)

12c Parallel Execution New Features: Hybrid Hash Distribution – Part 1

In this blog post I want to cover some aspects of the the new HYBRID HASH adaptive distribution method that I haven't covered yet in my other posts.As far as I know it serves two purposes for parallel HASH and MERGE JOINs, adaptive broadcast distribution and hybrid distribution for skewed join expressions. In the first part of this post I want to focus on former one.

1. Adaptive Broadcast Distribution For Small Left Row (more...)

Exadata & In-Memory Real World Performance Artikel (German)

Heute wurde auf "informatik-aktuell.de" ein aktueller Artikel von mir veröffentlicht. Es geht darin um die Analyse eines Falles bei einem meiner Kunden, der auf Exadata nicht die erwartete Performance erreicht hat.

In dem Artikel werden unterschiedliche Abfrage-Profile analysiert und erklärt, wie diese unterschiedlichen Profile die speziellen Features von Exadata und In-Memory beeinflussen.

Teil 1 des Artikels
Teil 2 des Artikels

Video Tutorial: XPLAN_ASH Active Session History – Part 3

The next part of the video tutorial explaining the XPLAN_ASH Active Session History functionality continuing the actual walk-through of the script output.

More parts to follow.

Parallel Execution 12c New Features Overview

Parallel Execution 12c New Features Overview

Oracle 12c is the first release since a couple of years that adds significant new functionality in the area of Parallel Execution operators, plan shapes and runtime features. Although 11gR2 added the new Auto DOP feature along with In-Memory Parallel Execution and Statement Queueing, the 12c features are more significant because they introduce new operators that can change both execution plan shape and runtime behaviour.

Here is (more...)

Webinar Followup

Thanks everyone who attended my recent webinar at AllThingsOracle.com.

The link to the webinar recording can be found here.

The presentation PDF can be downloaded here. Note that this site uses a non-default HTTP port, so if you're behind a firewall this might be blocked.

Thanks again to AllThingsOracle.com and Amy Burrows for hosting the event.

Video Tutorial: XPLAN_ASH Active Session History – Part 2

The next part of the video tutorial explaining the XPLAN_ASH Active Session History functionality has been published. In this part I begin the actual walk-through of the script output.

More parts to follow.


New Version Of XPLAN_ASH Utility – In-Memory Support

A new version 4.21 of the XPLAN_ASH utility is available for download. I publish this version because it will be used in the recent video tutorials explaining the Active Session History functionality of the script.

As usual the latest version can be downloaded here.

This is mainly a maintenance release that fixes some incompatibilities of the 4.2 version with less recent versions (10.2 and 11.2.0.1).

As an extra however, (more...)

Free Webinar "Oracle Exadata & In-Memory Real-World Performance"

It's webinar time again.

Join me on Wednesday, January 28th at AllThingsOracle.com for a session based on a real world customer experience.

The session starts at 3pm UK (16:00 Central European) time. The webinar is totally free and the recording will made available afterwards.

Here's the link to the official landing page where you can register and below is the official abstract:

Abstract

After a short introduction into what the Oracle Exadata Database Machine (more...)

Video Tutorial: XPLAN_ASH Active Session History – Introduction

I finally got around preparing another part of the XPLAN_ASH video tutorial.

This part is about the main funcationality of XPLAN_ASH: SQL statement execution analysis using Active Session History and Real-Time SQL Monitoring.

In this video tutorial I'll explain what the output of XPLAN_ASH is supposed to mean when using the Active Session History functionality of the script. Before diving into the details of the script output using sample reports I provide some overview and (more...)

"SELECT * FROM TABLE" Runs Out Of TEMP Space

Now that I've shown in the previous post in general that sometimes Parallel Execution plans might end up with unnecessary BUFFER SORT operations, let's have a look what particular side effects are possible due to this.

What would you say if someone tells you that (s)he just did a simple, straightforward "SELECT * FROM TABLE" that took several minutes to execute without returning, only to then error out with "ORA-01652 unable to extend temp segment", (more...)

Unnecessary BUFFER SORT Operations – Parallel Concatenation Transformation

When using Parallel Execution, depending on the plan shape and the operations used, Oracle sometimes needs to turn non-blocking operations into blocking operations, which means in this case that the row source no longer passes its output data directly to the parent operation but buffers some data temporarily in PGA memory / TEMP. This is either accomplished via the special HASH JOIN BUFFERED operation, or simply by adding BUFFER SORT operations to the plan. The (more...)

New Version Of XPLAN_ASH Utility

A new version 4.2 of the XPLAN_ASH utility is available for download.

As usual the latest version can be downloaded here.

There were no too significant changes in this release, mainly some new sections related to I/O figures were added.

One thing to note is that some of the sections in recent releases may require a linesize larger than 700, so the script's settings have been changed to 800. If you use corresponding settings (more...)

Heuristic TEMP Table Transformation

There are at least three different ways how the Oracle optimizer can come up with a so called TEMP table transformation, that is materializing an intermediate result set:- As part of a Star Schema transformation the repeated access to dimensions can be materialized- As part of evaluating GROUPING SETs intermediate result sets can be materialized- Common Subquery/Table Expressions (CTE, WITH clause)Probably the most common usage of the materialization is in (more...)

Parallel Execution Skew – Summary

I've published the final part of my video tutorial and the final part of my mini series "Parallel Execution Skew" at AllThingsOracle.com concluding what I planned to publish about the topic of Parallel Execution Skew.

Since all this was published over a longer period of time this post therefore is a summary with pointers to the material.

If you want to get an idea what the material is about, the following video summarizes the (more...)

New Version Of XPLAN_ASH Utility

A new version 4.1 of the XPLAN_ASH utility is available for download.

As usual the latest version can be downloaded here.

This version in particular supports now the new 12c "Adaptive" plan feature - previous versions don't cope very well with those if you don't add the "ADAPTIVE" formatting option manually.

Here are the notes from the change log:

- GV$SQL_MONITOR and GV$SQL_PLAN_MONITOR can now be customized in the
settings as table names in (more...)

Parallel Execution Skew – Addressing Skew Using Manual Rewrites

This is just a short note that the next part of the mini series about Parallel Execution skew has been published at AllThingsOracle.com.

After having shown in the previous instalment of the series that Oracle 12c added a new feature that can deal with Parallel Execution skew (at present in a limited number of scenarios) I now demonstrate in that part how the problem can be addressed using manual query rewrites, in particular the (more...)

12c Hybrid Hash Distribution with Skew Detection / Handling – Failing

This is just an addendum to the previous post demonstrating one example (out of many possible) where the join skew handling feature fails. The test case setup is the same as in the previous post.As mentioned in the AllThingsOracle.com article and in the introduction of the previous post, the feature at present only applies to a rather limited number of scenarios. To wrap things up and to give an idea what can happen (more...)

12c New Optimizer Features

Besides the officially available information about new optimizer features in 12c it is always a good idea to have a look at the internal optimizer parameters that show what features are enabled when running with OPTIMIZER_FEATURES_ENABLE = 12.1.0.1. Here is the list of internal optimizer parameters and fix controls that are different between 11.2.0.4 and 12.1.0.1:

Optimizer parameters:

_optimizer_partial_join_eval           partial join evaluation parameter                            
_optimizer_unnest_scalar_sq            enables (more...)

12c Hybrid Hash Distribution with Skew Detection / Handling

Oracle 12c introduces several new features in the area of Parallel Execution. Over the next couple of weeks I attempt to publish more about them - Jonathan Lewis for example already published a note about the new "PQ Replication" feature that applies to the BROADCAST distribution of small tables.One important new feature is the automatic skew handling for parallel joins. I've already given an overview of the feature in my mini-series "Parallel Execution Skew" (more...)