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SQL etc

Posted Jan 2, 2003

Database Performance and some Christmas Cheer - Page 2

By James Koopmann

Key Performance Metrics

When doing any form of database performance tuning, or applying the instructions from an article, please try and determine which of the following categories may be impacted. Most of the time more than one area will be impacted. (If you feel this list is incomplete or can't seem to make it work, please drop me a line).

How much is the database being asked to do? Do you know? You should! Workload is the combination of requests made upon the database. It is a great indicator for determining if everything is normal. If workloads are the same as always, and users are experiencing problems, it is safe to assume that something down the line processing user requests is not functioning properly.

If the workload has increased and people are having problems, the assumption can be made that an increase in workload will produce more of a strain on the system.

Workload is the collection of DDL (Data Definition Language) statements--the select, insert, update, and delete queries--which users and applications submit. Don't forget, it is also the administrative tasks that DBAs request of the database, everything from the scheduled backups, to the table that needs reorganization, to the indexes that have been rebuilt.

Back to our Christmas lights comparison. We need to:

  • Get (select) the lights from the garage
  • Go to the store and buy (insert) new lights or lawn ornaments
  • Replace (update) the burnt out bulbs from the current string of lights
  • Throw away (delete) any old or unusable lights.

Fixing the gutter to hang the lights on, or doing yard maintenance to clear a spot for the nativity scene could be compared to DDL.

Response Time:
Once the database acknowledges the request for work, it begins the work, and in a perfect world will complete the request. The time interval between the request and completion is the response time.

When stringing lights, if it takes two hours to go to the store, pick out the nativity scene, get home, and put it up, that is the response time to the request: "Honey, I would really like a nativity scene put in the front lawn this year."

As the database receives and processes requests, there is an underlying statistic that signifies the amount of requests that a database can handle over a period of time. This rate at which the requests can be performed is known as throughput. Throughput is a great indicator of productivity.

A string of lights has 200 bulbs, and takes five minutes to test for burned out bulbs. Your throughput is 200bulbs/5minutes, or 40bulbs/minute.

As a side note, if you get discouraged over the time it takes to put up all those lights, try equating the time and money you are forgoing if you were actually doing database administration work in a consulting role against the time and money you could spend to have someone else put up the lights. If the return on investment for you doing the Christmas lights is greater than someone else doing it, then great! If not, well, bah humbug.

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