Write-Ahead Log / Recovery Target

recovery_target

• What it does: Specifies the type of recovery target, with "immediate" option to end recovery as soon as a consistent database state is reached.
• Why it matters: This parameter provides a safe way to complete recovery at the earliest possible consistent point, which is useful for bringing up a standby server quickly or recovering from corruption without applying all available WAL. The "immediate" option stops recovery at the first transaction-consistent state found, which can significantly reduce recovery time when you don't need to reach a specific point in time.
• Ideal value & Best Practice: Typically not set (commented out) for most recovery scenarios. Use 'immediate' only when you want to recover to the earliest consistent state. For precise recovery, use more specific target parameters like recovery_target_time or recovery_target_lsn instead.

recovery_target_action

• What it does: Determines what action PostgreSQL takes when the recovery target is reached - pause, promote, or shut down.
• Why it matters: This parameter controls the server's behavior after completing recovery, which is crucial for operational procedures. "Pause" allows inspection before making the server available, "promote" automatically brings the server to full operation, and "shutdown" stops the server for additional configuration or verification.
• Ideal value & Best Practice: Default 'pause' is safest as it allows verification before proceeding. Use 'promote' for automated failover scenarios. Use 'shutdown' when you need to perform additional manual steps after recovery. Always test the chosen action in your specific environment.

recovery_target_inclusive

• What it does: Controls whether to include or exclude the exact transaction specified by the recovery target.
• Why it matters: This parameter provides precision in recovery operations. When set to true (include), recovery will include the target transaction. When false (exclude), it stops before applying the target transaction. This is particularly important for point-in-time recovery where you might want to include or exclude a specific problematic transaction.
• Ideal value & Best Practice: Default true (include). Set to false if you need to exclude a specific transaction that caused issues. For most point-in-time recovery scenarios, keeping it true provides the expected behavior of including all transactions up to the specified point.

recovery_target_lsn

• What it does: Specifies the exact Log Sequence Number (LSN) up to which recovery should proceed.
• Why it matters: LSN-based recovery provides the most precise recovery targeting, as LSNs are the fundamental internal identifiers for WAL locations. This is essential for advanced recovery scenarios where you need to recover to an exact position in the WAL stream, such as after a specific known good state or before a specific bad event.
• Ideal value & Best Practice: Use LSN values from your WAL information: '0/15000000'. Ensure you have accurate LSN information from backups or monitoring systems. This is the most precise but also most technical recovery method, requiring careful LSN management.

recovery_target_name

• What it does: Specifies a named restore point (created with pg_create_restore_point()) to recover to.
• Why it matters: Named restore points provide a user-friendly way to mark specific recovery points that can be easily referenced later. This is much more intuitive than remembering LSNs or timestamps, making it ideal for planned operations like major application upgrades or schema changes where you might need to roll back.
• Ideal value & Best Practice: Use named restore points for planned operations: 'before_upgrade'. Create restore points at strategic times using SELECT pg_create_restore_point('descriptive_name');. This method combines precision with human readability.

recovery_target_time

• What it does: Specifies a timestamp up to which recovery should proceed.
• Why it matters: Time-based recovery is the most commonly used method for point-in-time recovery (PITR) as it's intuitive and aligns with how humans think about when issues occurred. This allows recovery to a specific moment before data corruption, accidental deletions, or other time-specific problems.
• Ideal value & Best Practice: Use ISO 8601 format: '2024-01-15 14:30:00 EST'. Always include timezone information to avoid ambiguity. This is the recommended approach for most point-in-time recovery scenarios as it's both precise and understandable.

recovery_target_timeline

• What it does: Specifies which timeline to recover into, important for complex recovery scenarios involving multiple branches.
• Why it matters: PostgreSQL's timeline feature allows branching from recovery points, which is essential for advanced recovery strategies. This parameter lets you choose whether to continue in the current timeline or branch to a new one, which is crucial for managing complex recovery scenarios and avoiding WAL conflicts.
• Ideal value & Best Practice: Default 'latest' is usually correct. Specify a specific timeline number only when you need to recover to a branch other than the latest. Use 'current' to continue in the current timeline. Timeline management is important for sophisticated backup strategies.

recovery_target_xid

• What it does: Specifies a transaction ID up to which recovery should proceed.
• Why it matters: Transaction ID-based recovery provides another precise targeting method, useful when you know the specific transaction that caused issues or when you have transaction-level auditing. This can be more precise than time-based recovery for specific transaction-oriented recovery needs.
• Ideal value & Best Practice: Use when you have specific transaction information: '1234567'. Requires knowing the exact transaction ID that marks your recovery point. This method is less common than time-based recovery but can be useful in specific scenarios where transaction tracking is available.

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