LiteSpeed for SQL Server 8.9 - Installation Guide

Compression Levels

You can specify a compression level manually, or you can use Adaptive Compression to let LiteSpeed automatically select the optimal compression level. For more information, see Adaptive Compression.

LiteSpeed offers the following compression levels that allow you to specify compression from least compression to most compression, with a corresponding CPU trade-off.

Depending on your environment, the various algorithms will yield different results. When choosing a compression level, test various options to determine the best option for your environment. For more information, see Test Optimal Backup Settings.

Generally, the higher the compression ratio the higher the CPU utilization and potentially more compression. That is, the higher compression levels will look for longer patterns to compress, as well as perform more passes on the data.

The higher levels do not guarantee better compression ratios as the nature of the data dictates the final result. Therefore, some databases will get varying results as the level increases.

Additionally, if a higher level gets significantly better compression, it may actually perform faster than a lower level. Typically, the higher levels require more time for the backup.

NOTE: LiteSpeed supports backing up, restoring and shipping transaction logs of the databases encrypted with transparent data encryption (TDE). If you want to compress the backup, you should choose compression level 1 to minimize CPU, since using a higher level of compression will only cause CPU to increase without any real benefit on the backup file size. If you choose compression level 0, LiteSpeed will not attempt to compress the backup. Review the following for additional information:

• Its important to back up the database encryption key, because there is no way to recover the data without the key. LiteSpeed does not automatically export the encryption key. If needed, you can include the encrypted key file in the backup. For more information, see Back Up Databases.
• To further protect the backup, you can use LiteSpeed Encryption with TDE databases to add a secondary layer or protection to the backup. For more information, see Encryption Methods.

Adaptive Compression

With Adaptive Compression you do not have to run the Backup Analyzer wizard to determine the best compression level for a database. LiteSpeed will dynamically change the compression level during a backup in order to optimize for speed or size, while maximizing use of available CPU. If the server workload changes during the backup (change in CPU or Disk IO), Adaptive Compression automatically switches compression to maintain optimal performance.

You can select to optimize backups either for size or for speed:

• Optimize for speed—Backups complete in the least amount of time possible. Available CPU is leveraged to reduce backup size, but not at the expense of increased backup time. This is the default setting.
• Optimize for size—Backups are completed with higher compression while managing overall backup time to ensure backups do not take a long time to complete (when compared to optimizing for speed). In this mode, LiteSpeed allows the backup to complete more slowly if the reduction in speed results in a smaller backup file. This mode is designed for databases where a smaller backup is desired but managing how long the backup takes to complete is important as well.

NOTE: Adaptive Compression is only available with LiteSpeed 6.5 or later; Enterprise license.