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Transaction Log / Archive Log Volume

- not for DBA's but for Application-, Operations- and Change Managers

The time to understand those few pages is far less then the time for discusssions after an unplanned outage happened!

Yes, you are reading right! This paper is not for Database Administrators (DBA's) - they know that very well! They can explain you more details about that, but they can't prevent outages caused by Operations Team starting too many too large jobs at the same time and flooding the database with an untested and unmanageable amount of transaction log.

Therefore you need to understand those few pages.

Summary

Today in most cases restoring a database backup from last night and loosing all online-transactions since time of last backup isn't acceptable at all.

For this reason all professional database systems record changes additionally outside of the database in transaction log files, allowing to "roll forward" all changes since last backup and recovering even the last committed transaction.

But this feature causes some side effects, which if not understood by staff running the application this feature can cause serious problems and even unplanned outages which can't be prevented by an High Availability (HA) Cluster.

The purpose of this document is to raise awareness to Application Operations and Application Support that this necessary database feature can cause unplanned outages if if not understood and watched out during non-regular operations.

Summary......................................................................3
Background...................................................................4
   The Purpose and Principle of Transaction / Archive log files..............4
   What to measure during volume testing.....................................5
   What Application Operations needs to understand:..........................6
   What Change Managers should ask:..........................................6
Real Production Incidents....................................................7
   Example 1: Updating a huge table during Software Upgrade..................7
   Example 2: Sudden breakdown of WAN  performance to remote DR Data Centre.8
The Testing-Trap: Yes, we tested that!
     But the problem did not happen on the test system......................9

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