Month: April 2011

Time Spent, Time Wasted

Sometimes tuning a database can be rewarding.  I get great satisfaction when helping a user take their query from 10 minutes down to 3 seconds.  But it doesn’t always work that way.  Consider this recent exchange:

Developer to DBA Manager: The data…

Efficient analysis with IN operator

SQL developers frequently hear and realize that the subqueries are not efficient, avoid using them. Indeed, many times those SELECT statements, which contains subqueries in the WHERE or HAVING clause are not very efficient. But this not a general rule! I’d like to demonstrate that subqueries with IN operator and correlated subqueries can be very […]

Analyzing Oracle Data Warehouse with Analytic Functions I.

Introduction. The Rank family   The traditional SQL statements and functions do not provide strong support for analytic tasks. Basic business intelligence calculations such as moving averages, rankings and lead/lag comparisons have required extensive programming outside of standard SQL , often with performance challenges. From Oracle 8.1.6 Oracle provides powerful new family of functions which […]

Nulls in Ordering

You want to find out the tables with the highest number of rows in a database. Pretty simple, right? You whip up the following query:select owner, table_name, num_rowsfrom dba_tablesorder by num_rows;And, here is the output:OWNER       &…

Nulls in Ordering

You want to find out the tables with the highest number of rows in a database. Pretty simple, right? You whip up the following query:select owner, table_name, num_rowsfrom dba_tablesorder by num_rows;And, here is the output:OWNER       &…

How Smart is Your Smart Scan?

I was teaching the Oracle Database Machine Administration Workshop in London last week, when an interesting discussion arose concerning Exadata Smart Scan processing when the following situations arise: Migrated or Chained Rows Consistent Read (CR) Requests The discussion followed on from a situation that a delegate encountered when doing some routine maintenance on tables and […]

The eagle has landed

After 3 months of planning and logistics, the migration of uncompressed 600 TB’s of data from Europe to Asia has finished last weekend. Now our 2 X2-2 Racks is hosting 4 databases. Thanks for everybody who has  involved in this project with both their supports and critics.

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