Tuesday Nov 08, 2011

Lies, damned lies, and statistics

There was huge interest in our OOW session on Managing Optimizer Statistics. It seems statistics and the maintenance of them continues to baffle people. However, understanding and managing Optimizer statistics is key to optimal SQL execution. Knowing when and how to gather statistics in a timely manner is critical to maintaining acceptable performance. In order to clarify all of the information surrounding statistics we have put together a two part whitepaper on Optimizer statistics and the management of them.[Read More]

Thursday Oct 20, 2011

Optimizer Technical Papers

We recently got a comment about our paper on adaptive cursor sharing and cardinality feedback, in which the author wished for more technical papers from the optimizer team. We've actually published papers on a few different topics over the years, so we wanted to summarize and post links to them here. Unfortunately they are not all available online for free, but where possible, we've posted links to the full text.

Cost-Based Query Transformation in Oracle
Rafi Ahmed, Allison W. Lee, Andrew Witkowski, Dinesh Das, Hong Su, Mohamed Zait, Thierry Cruanes: Cost-Based Query Transformation in Oracle. VLDB 2006: 1026-1036
This paper talks about many of the query transformations in Oracle 11g which we have discussed here before, including join elimination, view merging, subquery unnesting, join predicate pushdown, join factorization, plus some others that we have not covered here before.  It also describes the cost-based framework itself, some of the challenges of transforming queries in a cost-based manner, and presents performance results for some experiments on a query workload from the Oracle E-Business Suite.

Optimizer Plan Change Management (full text)
Mohamed Ziauddin, Dinesh Das, Hong Su, Yali Zhu, Khaled Yagoub: Optimizer plan change management: improved stability and performance in Oracle 11g. PVLDB 1(2): 1346-1355 (2008)
This describes SQL plan management, which we discussed on here in a four-part SPM series.  The paper gives a bit more detail about the internals of SPM, plus analyzes the behavior of SPM on a large query workload from Oracle E-Business Suite.

Closing the Query Processing Loop in Oracle 11g
(full text)
Allison W. Lee, Mohamed Zait: Closing the query processing loop in Oracle 11g. PVLDB 1(2): 1368-1378 (2008)
This paper discusses adaptive cursor sharing and cardinality feedback, plus the general concept of using feedback from execution to improve plan selection.  We've covered both of these topics on here before, but the paper also includes an analysis of the performance impact of the two features on a query workload from Oracle E-Business Suite.

Efficient and scalable statistics gathering for large databases in Oracle 11g
Sunil Chakkappen, Thierry Cruanes, Benot Dageville, Linan Jiang, Uri Shaft, Hong Su, Mohamed Zait: Efficient and scalable statistics gathering for large databases in Oracle 11g. SIGMOD Conference 2008: 1053-1064
This paper discusses two major improvements to statistics gathering in 11g -- approximate NDV and incremental statistics gathering.  We've discussed both of these topics here before, but the paper has some additional details of the algorithms, plus results of experiments on a few different data sets.

Enhanced Subquery Optimizations in Oracle, VLDB 2009 (full text)
Srikanth Bellamkonda, Rafi Ahmed, Andrew Witkowski, Angela Amor, Mohamed Zait, Chun Chieh Lin: Enhanced Subquery Optimizations in Oracle. PVLDB 2(2): 1366-1377 (2009)
This paper talks about several of the newer subquery optimizations in Oracle.  We talked about basic subquery unnesting in two posts here a while ago, and alluded to some of the other subquery transformations we perform -- this paper talks about all of those.  It also talks about a new form of join elimination which we introduced in 11gR2.  Nearly all of the topics in this paper are NOT covered here on the blog yet, but we hope to fix that soon!

For future reference, we will be adding a new section on the right side of the page called "Optimizer Technical Papers" with links to all of these papers.

Monday May 09, 2011

Explain the Explain Plan white paper finally published!

New Oracle Optimizer white paper, Explain the Explain Plan, published on OTN.

[Read More]

Monday Mar 28, 2011

What happened to the Optimizer white papers on OTN?

We have gotten a lot of questions recently about what happened to the Optimizer white papers that use to be on OTN. The white papers are still there but the URL has changed slightly, which is causing the problem. Here are new URL's for the most recent Optimizer white papers:

SQL Plan Management in Oracle Database 11g

Upgrading from Oracle Database 9i to 10g: What to expect from the Optimizer

Upgrading from Oracle Database 10g to 11g: What to expect from the Optimizer

Wednesday Feb 27, 2008

What to expect from the Optimizer when upgrading from Oracle Database 9i to 10g

One of the most daunting activities a DBA can undertake is upgrading the database to a new version. Having to comprehend all of the new features and to deal with potential plan changes can be overwhelming. In order to help DBA's upgrade from Oracle Database 9i to 10g a new whitepaper called "Upgrading from Oracle Database 9i to 10g: What to expect from the Optimizer" has recently been posted on Oracle Technology Network (OTN). This paper aims to explain in detail what to expect from the CBO when you upgrade from Oracle database 9i to 10g and describes what steps you should take before and after the upgrade to minimize any potential SQL regressions. This is a must read for any DBA planning on upgrading from 9i to 10g in the near future!

About

The Oracle Optimizer blog is written by members of the Optimizer development team. The goal of this blog is to provide an insight into the workings of the Optimizer and the statistics it relies on. The views expressed on this blog are our own and do not necessarily reflect the views of Oracle and its affiliates. The views and opinions expressed by visitors on this blog are theirs solely and may not reflect ours.

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