Indexing Points to Remember

Indexing depends upon the queries in the application.

There is no one-size-fits-all break-even point for indexed versus table scan access. If only a few rows are being accessed, the index will be preferred.

If almost all the rows are being accessed, the full table scan will be preferred. In between these two extremes, your “mileage” will vary.

A concatenated index is more useful if it also supports queries where not all columns are specified. For (more...)

Log Buffer #406, A Carnival of the Vanities for DBAs

This Log Buffer Edition covers blog posts from various bloggers of Oracle, SQL Server and MySQL.

Oracle:

Sync tables: generate MERGE using Unique constraint.
What Hardware and Software Do YOU Want Oracle to Build?
There were a number of new features introduced in Ops Center 12.2.2. One of the shiny ones is an expansion of the backup and recovery capabilities to include Proxy Controllers.
Want to Be a Better Leader? Answer One Question.
(more...)

Histograms Tidbits

Make sure histograms exist on columns with uneven data distributions to ensure that the optimizer makes the best choice between indexes and table scans.




For range scans on data that is not uniformly distributed, the optimizers’ decisions will be improved by the presence of a histogram.

Histograms increase the accuracy of the optimizer’s cost calculations but increase the overhead of statistics collections. It’s usually worth creating histograms for columns where you believe the data will (more...)

Who is a DBA Leader?

Sitting behind a big mahogany table, smoking Cuban Cigar, glaring at the person sitting across, one hand taking the receive of black phone to right ear, and the other hand getting the mobile phone off the left ear can be the image of a DBA boss in any white elephant government outfit, but it certainly cannot work in organization made up of professionals like database administrators. And if such image or similar image is working (more...)

Script for Exadata I/O Report

select function_name,sum(SMALL_READ_MEGABYTES)/1024 SM_Read_GB,
sum(SMALL_WRITE_MEGABYTES)/1024 SM_Write_GB,
sum(LARGE_READ_MEGABYTES)/1024 LG_Read_GB, sum(LARGE_WRITE_MEGABYTES)/1024 LG_Write_GB,
sum(LARGE_READ_REQS) LG_Read_Requests,
sum(LARGE_Write_REQS) LG_Write_Requests
from v$iostat_function_detail
group by function_name;

Log Buffer #404, A Carnival of the Vanities for DBAs


With new year already in fast gear, bloggers are sparing no stone unturned to come up with innovative ideas. This Log Buffer edition is keeping pace with them as always.

Oracle:

While playing with 12c Scott tried the upgrade to the DEFAULT column syntax that now allows sequences.
This is an age old question and of course the answer depends on how you say “SQL”.
Happy New Year! Upgraded 12.1.0.1 (more...)

Log Buffer #402, A Carnival of the Vanities for DBAs

This Log Buffer edition hits the ball out of park by smashing yet another record of surfacing with a unique collection of blog posts from various database technologies. Enjoy!!!

Oracle:

EM12c and the Optimizer Statistics Console.
SUCCESS and FAILURE Columns in DBA_STMT_AUDIT_OPTS.
OBIEE and ODI on Hadoop : Next-Generation Initiatives To Improve Hive Performance.
Oracle 12.1.0.2 Bundle Patching.
Performance Issues with the Sequence NEXTVAL Call.

SQL Server:

GUIDs GUIDs everywhere, but how (more...)