Background Writer

Overview

The Background Writer page shows important configuration information as well as performance metrics related to the background writer.

Data

Top-left Table Section

• Health – Shows the overall health of the background writer.
• Alarms – Provides counts of the alarms for this agent, separated by severity.
• Last Stat Reset – Time when statistic counters for the background writer were last reset.
• Checkpoint Timeout – Maximum amount of time between automatic WAL checkpoint writes. If checkpoint segment limit is not reached before this time, a checkpoint will be triggered.
• BGWriter Delay – Delay between activity rounds for the background writer.
• BGWriter LRU Max Pages – Maximum number of pages written per activity round.
• BGWriter LRU Multiplier –Multiplier used to calculate the number of dirty buffers written for a given activity round

Graphs

• Total Buffers Allocated – Number of buffers allocated for use by the background writer.
• Buffer Write Comparison – Compares number of buffers written by a backend vs. being written by the background writer.
• Buffer Write Method Pct – Compares percent of buffers written by a backend vs. percent of buffers written during normal checkpoints.
• % of Checkpoints Required - Percent of checkpoints executed that were required. Low percent indicates system has not been active enough to reach WAL segment limit before reaching the checkpoint timeout limit.
• Checkpoint Interval – Average elapsed time between checkpoints.
• Total Written Bytes Rate – Rate of total data written into Write Ahead Log.
• Avg Checkpoint Write Size – Average amount of data written into WAL during checkpoints.
• # of Time Reached Buffer Limit – Number of times the background writer stopped a cleaning scan because it had written too many buffers.
• Fsync Calls From Backends – Compares number of times a backend had to execute its own fsync call (normally handled by the background writer even when the backend does its own write).