Write-Ahead Log / Summarization

summarize_wal

• What it does: Controls whether the WAL summarizer process is started, which analyzes WAL records to identify changed data blocks and enables efficient incremental backup functionality.
• Why it matters: This parameter is essential for supporting incremental backups in PostgreSQL. When enabled, the summarizer process runs in the background and creates summary files that track which database blocks have been modified between specific points in the WAL stream. This allows backup tools to perform incremental backups by only copying the blocks that have changed since the last backup, significantly reducing backup size and duration compared to full backups.
• Ideal value & Best Practice: Default off. Set to on when you plan to use incremental backup solutions. Requires PostgreSQL 17 or later. Ensure you have monitoring in place to track the summarizer process health and performance impact.

wal_summary_keep_time

• What it does: Sets the duration for which WAL summary files should be retained before being automatically cleaned up.
• Why it matters: This parameter balances between storage usage and backup flexibility. WAL summary files accumulate over time and can consume significant storage space if kept indefinitely. However, keeping summaries for longer periods provides more flexibility for incremental backup strategies, allowing you to use older backup points as the base for new incremental backups. Proper retention planning ensures you have sufficient summary data for your backup strategy without wasting storage space.
• Ideal value & Best Practice: Default 0 (no automatic cleanup). Set based on your backup retention policy: 7d for weekly full backups, 30d for monthly backup cycles. Consider your storage capacity and how far back you might need to create incremental backups from different points in time. Monitor disk usage and adjust accordingly.

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