Stairway to Transaction Log Management in SQL Server
When things are going well, there is no need to be particularly conscious of what the transaction log does or how it works. You just need to be confident that every database has the correct backup regime in place. When things go wrong, an understanding of the transaction log is important for taking corrective action, particularly when a point-in-time restore of a database is required, urgently! Tony Davis gives just the right level of detail that every DBA should know.
- The transaction log is used by SQL Server to maintain data consistency and integrity. If the database is not in Simple-recovery mode, it can also be used in an appropriate backup regime to restore the database to a point in time.
- In order to make it easier to understand truncation, space reuse and fragmentation in the log file, Tony gives a brief explanation of how the transaction log works.
- This article discusses the different types of backup and recovery models and gives the essential facts that will guide you to being able to achieve a recovery of a database to a point in time.
- Tony describes in more detail the SIMPLE recovery model, and the way it works, its advantages and disadvantages.
- In FULL recovery mode it is possible to do a point-in-time restore of a database. It is thankfully a rare event. Tony explains what's involved
- A DBA may consider switching a database to the BULK_LOGGED recovery model in the short term during, for example, bulk load operations. When a database is operating in the BULK_LOGGED model these, and a few other operations such as index rebuilds, can be minimally logged and will therefore use much less space in the log
- This level will examine the most common problems and forms of mismanagement that lead to excessive growth of the transaction log.
- This level takes a deeper look at how log fragmentation can affect the performance of operations that need to read the log, such as log backups, or the crash recovery process.
- Our major goal in terms of log maintenance for all databases under our care is to optimize for write performance, in order to support all activities that require SQL Server to write to the log, including data modifications, data loads, index rebuilds, and so on. However, it's also important to keep an eye on possible log fragmentation, which, as described previously, can affect the performance of processes that need to read the log, such as log backups and the crash recovery process.