Oracle Scratchpad

Public Appearances

12th Oct 2017 London, UK: I’ll be speaking at a UKOUG SIG event, presenting “Basic Guide to Trouble-shooting”:

The performance questions that come up on the Internet often say things like: “This batch job is taking too long should I increase the db_file_multiblock_read_count?”; and you are often left wondering why such a specific idea was seen as an appropriate way to address the time spent in the batch. It’s too easy to fall into the trap of trying to fix the problem without really knowing what the problem is and where to focus the attention.

This presentation outlines a mental pattern for trouble-shooting:

  • First – what problem are we trying to solve
  • Second – why has that come to our attention as a problem
  • Third – what tools do we use to get better information about the problem
  • Finally – what are we likely to see and how do we interpret it.


4th – 6th Dec 2017 Birmingham, UK: I’ll be speaking at UKOUG Tech17. I’ll also be chairing the CBO Panel session and the CBO round-table.

Monday 4th:: 9:00 – 9:50: “Index Statistics and Column Groups”.

The optimizer has a history of picking bad execution plans because of two critical defects. The first is due to over-estimating the cost of using an index, the second is due to overestimating the number of distinct combinations of values that might appear for multi-column predicates. In recent versions of Oracle we can now address (at least in part) both these problems, the first through the “table_cached_blocks” preference, the second through column group (extended) stats. As a bonus the session also demonstrates how we can take advantage of the latter to help us drop or change indexes, and reduce the cost of gathering stats on indexes.

Monday 4th:: 14:25 – 15:15: CBO Roundtable

Tuesday 5th:: 9:00 – 9:50: CBO Panel Session with Maria Colgan, Nigel Bayliss, Richard Foote, and Chris Antognini.  With Neil Chandler and Martin Widlake running the audience and reading out questions.

Wednesday 6th:: 12:25 – 13:15: “Parallel Execution”

The mechanics of Parallel Execution are not trivial, and it’s quite hard to work out what Oracle is telling us in a parallel execution plan. This session describes some of the critical features of how parallel execution works, explains how to read parallel execution plans, and how to find critical performance information that isn’t immediately available in a typical plan. To get the best from this session you will need to be fluent in reading serial execution plans.

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