12c Parallel Execution New Features: Parallel FILTER Subquery Evaluation – Part 3: The Optimizer And Distribution Methods

As mentioned in the first and second part of this instalment the different available distribution methods of the new parallel FILTER are selected automatically by the optimizer - in this last post of this series I want to focus on that optimizer behaviour.It looks like there are two new optimizer related parameters that control the behaviour of the new feature: "_px_filter_parallelized" is the overall switch to enable/disable the new parallel filter capability - and (more...)

New Version Of XPLAN_ASH Utility

A new version 4.22 of the XPLAN_ASH utility is available for download.

As usual the latest version can be downloaded here.

This version primarily addresses an issue with 12c - if the HIST mode got used to pull ASH information from AWR in 12c it turned out that Oracle forgot to add the new "DELTA_READ_MEM_BYTES" columns to DBA_HIST_ACTIVE_SESS_HISTORY - although it got officially added to V$ACTIVE_SESSION_HISTORY in 12c. So now I had to implement (more...)

IT Tage 2015 – "Analysing and troubleshooting Parallel Execution" presentation material

Thanks to all attending my presentation "Analysing and troubleshooting Parallel Execution" at the IT Tage conference 2015 in Frankfurt, Germany. You can download the presentation material here in Powerpoint of PDF format, as well as check the Slideshare upload.

Note that the Powerpoint format adds value in that sense that many of the slides come with additional explanations in the notes section.

If you are interested in more details I recommend visiting this post which (more...)

DOAG 2015 – "Oracle 12c Parallel Execution New Features" presentation material

Thanks to the many attendees that came to my presentation "Oracle 12c Parallel Execution New Features" at the DOAG conference 2015. You can download the presentation material here in Powerpoint of PDF format, as well as check the Slideshare upload.

Note that the Powerpoint format adds value in that sense that many of the slides come with additional explanations in the notes section.

If you are interested in more details I recommend visiting this post (more...)

12c Parallel Execution New Features: Parallel FILTER Subquery Evaluation – Part 2: Distribution Methods

Picking up from the first part of this instalment I'll focus in this post on the available distribution methods for the new parallel FILTER subquery feature.In this post I won't go into the details how the optimizer selects the distribution method automatically - this will be covered in the last part.Here I merely describe the different available methods and how to control them using the new PQ_FILTER hint, which is also mentioned in (more...)

Parallel Projection

A recent case at a client reminded me of something that isn't really new but not so well known - Oracle by default performs evaluation at the latest possible point in the execution plan.So if you happen to have expressions in the projection of a simple SQL statement that runs parallel it might be counter-intuitive that by default Oracle won't evaluate the projection in the Parallel Slaves but in the Query Coordinator - even (more...)

12c Parallel Execution New Features: Parallel FILTER Subquery Evaluation – Part 1: Introduction

12c introduces another interesting new Parallel Execution feature - the parallel evaluation of FILTER subqueries. In pre-12c FILTER subqueries always had to be evaluated in the Query Coordinator. This had several consequences, in particular the data driving the FILTER subquery always had to flow through the Query Coordinator, and hence represented a forced serial execution part of a parallel execution plan. This limitation also meant that depending on the overall plan shape the parallel plan (more...)

Video Tutorial: XPLAN_ASH Active Session History – Part 6

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.

12c Parallel Execution New Features: 1 SLAVE distribution

When certain SQL features get used in pre-12c versions that force non-parallel evaluation, like using ROWNUM or certain Analytic Functions like LAG/LEAD, then - depending on the overall plan shape - Oracle can start to decompose the parallel execution plan into several so called DFO trees (If you want learn more about DFO trees and DFOs I recommend watching my online tutorial on my Youtube channel).Now having multiple DFO trees in a single (more...)