Background I/O activities

Background I/O activities do not service SQL requests directly. Many of these activities are essential to maintain database consistency and other aspects of database server operation. However, they create overhead in the CPU and take up I/O bandwidth.

These overhead activities take time away from queries and transactions. If you do not configure background I/O activities properly, too much overhead for these activities can limit the transaction throughput of your application.

The following list shows some background I/O activities:
  • Checkpoints
  • Logging
  • Page cleaning
  • Backup and restore
  • Rollback and recovery
  • Data replication
  • Auditing

Checkpoints occur regardless of whether much database activity occurs; however, they can occur with greater frequency as activity increases. Other background activities, such as logging and page cleaning, occur more frequently as database use increases. Activities such as backups, restores, or fast recoveries occur only as scheduled or under exceptional circumstances.

For the most part, tuning your background I/O activities involves striking a balance between appropriate checkpoint intervals, logging modes and log sizes, and page-cleaning thresholds. The thresholds and intervals that trigger background I/O activity often interact; adjustments to one threshold might shift the performance bottleneck to another.

The following sections describe the performance effects and considerations that are associated with the configuration parameters that affect these background I/O activities.

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