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12c Adaptive Cursor Sharing
This is neither a 12c new feature you are still not aware of nor an extension of the 11 g Adaptive Cursor Sharing I am going to have the scoop to announce it. It is rather something I have pointed out...
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BIND_EQUIV_FAILURE – Or when you will regret using Adaptive Cursor Sharing
Previously, when I was asked to define the Adaptive Cursor Sharing(ACS) feature I’ve often used the following definition: “it represents an answer to the always threating and challenging Oracle task of...
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The dark side of using bind variables : sharing everything
An interesting academic situation happened last week which I, honestly believe, is worth a blog article as far as experienced DBA have spent time trying to solve it without success. An overnight job...
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Parallel refreshing a materialized view
I have been asked to troubleshoot a monthly on demand materialized view refresh job which has got the bad idea to crash with the ORA-01555 error after 25,833 seconds (more than 7 hours) of execution....
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Real time SQL monitoring limitation
I was trying to explain a performance deterioration of a very complex query honoured via an execution plan with 386 operations (386 lines). From where would someone start deciphering this complex and...
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Index Efficiency
I used Jonathan Lewis script to locate degenerated indexes –-or indexes that are occupying more space than they should–. Among those indexes I have isolated this one: 16:20:33:TABLE1 - PK_TAB1 Current...
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Extended Statistics Part I : histogram effect
Extended statistic, also known as column group extension, is one of the important statistic improvements introduced with Oracle 11g. While Oracle Cost Based Optimizer is able to get a correct single...
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SUBQ INTO VIEW FOR COMPLEX UNNEST
If you are a regular reader of Jonathan Lewis blog you will have probably came across this article in which the author explains why an “OR subquery” pre-empts the optimizer from unnesting the subquery...
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Why Dynamic Sampling has not been used?
Experienced tuning guys are known for their pronounced sense of looking at details others are very often ignoring. This is why I am always paying attention to their answers in otn and oracle-l list....
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Real Time SQL Monitoring oddity
This is a small note about a situation I have encountered and which I thought it is worth sharing with you. There was an insert/select executing in parallel DOP 16 on a 11.2.0.3 Oracle database for...
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Don’t pre-empt the CBO from doing its work
This is the last part of the parallel insert/select saga. As a reminder below is the two preceding episodes: Part 1: where I have explained why I was unable to get the corresponding SQL monitoring...
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Stressed ASH
It is well known that any record found in dba_hist_active_session_history has inevitably been routed there from v$active_session_history. If so, then how could we interpret the following cut & past...
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Degree of Parallelism is 16 because of table property
I have been pleasantly surprised by the following Note at the bottom of an execution plan coming from a 12.1.0.2.0 Oracle instance SQL> select * from v$version; BANNER CON_ID...
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Flash back causing library cache: mutex X
Recently one of our applications suffered from a severe performance issue. It is an application running on a database(11.2.0.4.0) used to validate a pre-production release. This performance issue has...
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Adaptive Cursor Sharing triggering mechanism
Inspired by Dominic Brooks’ last post on SQL Plan Management choices, I decided to do the same work about my thoughts on Adaptive and Extended Cursor Sharing triggering mechanism: Once a cursor is bind...
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Cardinality Feedback: a practical case
Here it is an interesting case of cardinality feedback collected from an 11.2.0.3 running system. A simple query against a single table has a perfect first execution response time with, according to...
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CBO decision: unique or non-unique index?
I have been asked to look at one of those few particular frustrating situations that only running systems can procure. It is an update of a single table using a complete set of its primary key columns...
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Bind aware secret sauce (again)
I am sure many of you have already become bored by my posts on adaptive cursor sharing. I hope this article will be the last one :-). In part III of the installment I was unable to figure out the...
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Basic versus OLTP compression
If you are going to archive a table having a very large amount of data from a running system into a historical table and you expect from this archived table to be read-only then you have better to use...
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Oracle Optimizer and SPM plan interaction
Continuing in the inspiration instilled into me by Dominic Brooks’ post on SQL Plan Management choices, I decided to picture the Oracle CBO behavior in presence of enabled and accepted SPM plan(s)...
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