Original Post can be viewed at Optimizer Choosing Nested-Loop Joins Instead of Hash-Joins

In one of my databases, one application query suddenly started to pick Nested-Loop joins instead of Hash-Joins and took almost 6 hours to complete which gets completed in less than 10 secs with Hash-Joins. The same query in another similar database with same configuration and same data is doing fine and using hash joins. There is [...]

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Original Post can be viewed at User Sessions stuck on resmgr:cpu quantum wait event

We were experiencing lot of session getting stuck on resmgr:cpu quantum in our database. In fact at a time we had 70 sessions which were stuck on this wait event and our cpu load average was touching 60 Checking active resource plan, we found that DEFAULT_MAINTENANCE_PLAN was active. As per 11g Docs In this plan, [...]

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Original Post can be viewed at Plan Stability using Sql Profiles and SQL Plan Management

PLAN STABILITY How many times you have noticed a query using Index X when you wanted it to use index Y or query performing Nested Loop join when Hash Join would have completed the query much faster.Or take a scenario when the application suddenly starts using wrong plan after database restart. To solve all these [...]

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Original Post can be viewed at V$SQL_SHARED_CURSOR in 11.2.0.2

Oracle 11.2.0.2 has introduced new column “REASON” to V$SQL_SHARED_CURSORS. I came across this extremely useful column while debugging multiple child cursor issue (11.2.0.2 seems to have too many bugs which can cause multiple child cursors). As per documentation , REASON column has been introduced in 11.2.0.2 REASON - CLOB Child number, id, and reason the [...]

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Original Post can be viewed at Oracle Database Appliance Introduced

Oracle has introduced it new product: ODA (Oracle Database Appliance) I was not able to join Oracle President Mark Hurd’s webcast where he supposed to announce a new Oracle product[It was at 1AM my time and I was sleeping], now viewing this webcast HERE Kerry Osborne has shared information about this product, click link to [...]

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Original Post can be viewed at Performance Management Guide on AIX

While trying to find the amount of physical memory used by oracle process on AIX, I got reference of a document from Metalink: Performance Management Guide It tell us about which process is using how much memory and how to interpret the output of commands like: vmstat, svmon, ps on AIX. Also, to get more [...]

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Original Post can be viewed at ORA-01722 with Full Table Scan

My application developers approached me with an issue which is very unique to me. They were complaining about a query which was failing with ORA-01722 “invalid number” after an upgrade to 11.1.0.7 from 10.2.0.4. The syntax of the query is like: select max(a) from t1 where c1<>'abc' and c2=12345 and c3='Y' and c4='xyz'; This query [...]

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Original Post can be viewed at October 2010 Blogroll Report

It’s been time since we saw log-buffer edition with last being published on 1st October 2010 and  Coskan’s weekly blogroll report I found them really useful to read top blog articles for week. So I decided to tag few articles posted in October 2010 which I  had read and found useful. I am subscribed to [...]

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Original Post can be viewed at Sqlplus connection on AIX taking too long

Recently we faced a performance issue, where in sqlplus connection from application server A (AIX 5.3) to Database server DB (different physical server,10gR2 on AIX 5.3) was taking nearly 1-2 minutes.  We did some quick check’s to narrow down the problematic area.i.e Is it network or database server or some issue with application server? 1)Vmstat [...]

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Original Post can be viewed at GATHER_STATS_JOB – Is it enabled?

Few days back , Martin had posted a series of post on a issue where GATHER_STATS_JOB was failing silently for a large object. If you have missed it, you can check following links Automated statistics gathering silently fails http://mwidlake.wordpress.com/2009/07/20/automated-statistics-gathering-silently-fails/ Automated Statistics Gathering Silently Fails #2 http://mwidlake.wordpress.com/2009/07/23/automated-statistics-gathering-silently-fails-2/ Automatic Statistics Gathering Fails #3   http://mwidlake.wordpress.com/2009/07/29/automatic-statistics-gathering-fails-3/ Automated statistics [...]

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Original Post can be viewed at Mview Complete Refresh and Atomic_refresh parameter

This post discusses issue faced by me while working on Materialized view (mview) creation at new site(database). Starting Oracle 10g, how atomic_refresh works with complete refresh has undergone a change. Atomic_refresh parameter is to allow either all of the tasks of a transaction are performed or none of them (Atomicity). If set to TRUE, then [...]

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Original Post can be viewed at dbms_stats.copy_table_stats does not alter low/high value

I was working on a performance issue arising due to missing table stats on a new partition for large Partitioned table.This was a 10.2.0.4 database on IBM AIX 5L. So as to resolve the issue , I used dbms_stats.copy_table_stats to copy the stats to new parition from the previous partition. EXEC DBMS_STATS.COPY_TABLE_STATS (‘owner’, ‘tabname’, ‘SourcePart’, [...]

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Original Post can be viewed at You Don’t need SysDBA privilege to run Awrrpt..

Well I tried to Sensationalize this post by using such a heading Though I just wanted to point out that Awrrpt script can be run without sysdba privilege too. Actually if you open awrrpti.sql script , it contains following line Rem NOTES Rem Run as SYSDBA. Generally this script should be invoked by awrrpt, Rem [...]

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Original Post can be viewed at Connections to DataBase Hang Including “/ as sysdba”

Recently I faced one issue where all the connection to database hung and it was also not possible to login to database using “/ as sysdba”. To get access of sqlplus I used the following syntax: $ sqlplus -prelim / as sysdba With “prelim” option we can run some commands which will help in collection [...]

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Original Post can be viewed at Index Access best approach?? Not Always…

There is a common misconception that Index access is the best access method for query execution. This approach leads to people concentrate on removing Full Table Scans (FTS) from the Query execution plan. I recently worked on a performance tuning issue where I found such scenario. Basically customer was trying to generate report for 3 [...]

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Original Post can be viewed at Resolving Shutdown Immediate Hang Situations

Many times Oracle DBA’s are faced with a situation where shutting down the instance with shutdown immediate seems to take infinite time and gives a impression that the session is hung. In most of the cases this is not a hang. Hang can be defined as a scenario when few sessions/processes are waiting on some [...]

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Original Post can be viewed at Tracing Sessions with Event 10046

10046 Event is used to trace SQL statements (similar to sql_trace=true) with additional details depending on the tracing level which is specified. 10046 EVENT levels: 1 – Enable standard SQL_TRACE functionality (Default) 4 – As Level 1 PLUS trace bind values 8 – As Level 1 PLUS trace waits 12 – As Level 1 PLUS [...]

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Original Post can be viewed at Sign on Letter to Larry Ellison on AWR and ASH Licensing

While surfing across the blog’s, I found this particular link, a compaign which is aimed at getting free access to the ASH and AWR reports. I believe most of us know that we need to pay extra fees for the Diagnostic Tuning Pack which also includes ASH and AWR report. (If you’re not already familiar [...]

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Original Post can be viewed at HW enqueue contention with LOB

DefinitionEnqueues are local locks that serialize access to various resources. Enqueue wait event indicates a wait for a lock that is held by another session (or sessions) in an incompatible mode to the requested mode. HW Enqueue – High Watermark enqueue is acquired when a segment’s high water mark is moved, which will normally happen [...]

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Original Post can be viewed at Diagnostics For Database Hang

Many times Oracle DBA’s are in a situation when the database is hung and does not seem to be responding. In some scenarios, state is such that you cannot even connect to the sqlplus session. Majority people restart the database (Sometimes I wonder if this is due to the fact that most of us started [...]

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