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Native Flashback

[ AliSQL | English | 中文 ]

Native Flashback lets an InnoDB query read retained historical data with AS OF TIMESTAMP. It builds a consistent historical read view from snapshot records and retained undo, so accidental data changes can be investigated or recovered without first restoring a backup and replaying binlogs on another server.

The settings below apply to self-managed AliSQL 8.0.44. For RDS MySQL versions and parameters, see Alibaba Cloud RDS MySQL.

How It Works

AliSQL periodically records an InnoDB snapshot and retains the undo needed to reconstruct older row versions. An AS OF TIMESTAMP query selects a snapshot from that history and uses its read view for a consistent InnoDB read.

The requested wall-clock time and the selected snapshot need not be identical. innodb_rds_flashback_allow_gap limits the acceptable difference, and innodb_rds_flashback_print_warning controls whether a non-exact match produces a warning.

Enable Native Flashback

Snapshot generation requires both of the following values:

  • innodb_rds_flashback_task_enabled=ON
  • innodb_undo_retention>0

The background thread is created at server startup when either value is enabled. If the server starts with the task disabled and retention set to zero, changing both variables later does not create the missing thread. Configure both values before startup:

[mysqld]
innodb_rds_flashback_task_enabled=ON
innodb_undo_retention=3600
innodb_rds_flashback_interval=1

innodb_rds_flashback_enabled=ON is the query gate and is enabled by default. It does not generate snapshots or retain undo by itself. innodb_rds_flashback_task_stop_all=ON pauses snapshot creation and history cleanup even when the other controls are enabled.

After startup, confirm the effective values:

SHOW GLOBAL VARIABLES LIKE 'innodb_rds_flashback%';
SHOW GLOBAL VARIABLES LIKE 'innodb_undo_retention';

Wait for snapshot history to cover the target time before running a historical query.

Query Historical Data

SELECT id, status
FROM orders AS OF TIMESTAMP DATE_SUB(NOW(), INTERVAL 5 MINUTE)
WHERE customer_id = 1001;

The timestamp expression must be constant for one statement execution and evaluate to a timestamp value.

To recover data, write the historical result into a separate table first:

CREATE TABLE recovered_orders LIKE orders;

INSERT INTO recovered_orders
SELECT *
FROM orders AS OF TIMESTAMP '2026-07-16 10:00:00';

Validate row counts and business invariants before replacing production data. Quiesce application reads and writes before using RENAME TABLE, and keep the original table under a backup name until the recovered data is verified.

Inspect Snapshot History

Procedure Result or action
CALL dbms_admin.analyze_flashback_snapshots() Return the minimum timestamp, maximum timestamp, and total undo-space usage reported by InnoDB in MiB
CALL dbms_admin.show_flashback_snapshots(ts, order, limit) List snapshot transaction ID, timestamp, and read view; order is ASC or DESC; requires SUPER
CALL dbms_admin.del_flashback_snapshots(ts, order) Delete matching snapshot history; order is ASC or DESC; requires SUPER

Use the analysis procedure to confirm that a target timestamp is inside the retained window before recovery.

Variables

All variables below are global, dynamic InnoDB plugin variables. Startup configuration is still required to ensure that the background thread is created.

Variable Default Range or unit Description
innodb_rds_flashback_task_enabled OFF Boolean Participate in snapshot generation; generation also requires nonzero undo retention
innodb_rds_flashback_task_stop_all OFF Boolean Pause all snapshot-history work
innodb_rds_flashback_interval 1 1 to 86400 seconds Snapshot generation interval
innodb_rds_flashback_enabled ON Boolean Allow AS OF TIMESTAMP queries
innodb_rds_flashback_allow_gap 30 0 to UINT32_MAX minutes Maximum gap between the requested time and selected snapshot
innodb_rds_flashback_print_warning ON Boolean Warn when a non-exact snapshot is selected
innodb_undo_retention 0 0 to UINT32_MAX seconds Undo retention target; snapshot generation also requires a nonzero value
innodb_undo_space_supremum_size 10240 0 to UINT32_MAX MiB Undo-space ceiling used by retention cleanup
innodb_undo_space_reserved_size 0 0 to UINT32_MAX MiB Reserved undo-space threshold

Boundaries and Operations

  • AS OF TIMESTAMP is supported only for SELECT table references on InnoDB base tables.
  • Temporary tables, views, FOR UPDATE, and LOCK IN SHARE MODE are not supported.
  • A time outside retained history returns ER_SNAPSHOT_OUT_OF_RANGE.
  • DDL that changes the visible primary-key record can make an older snapshot incompatible and return ER_FLASHBACK_PK_INVISIBLE. Historical access across arbitrary DDL is not guaranteed.
  • Undo retention is a target, not an unconditional guarantee. Space thresholds and workload pressure can shorten the effective history window.
  • Retaining more undo consumes storage and can increase purge work. Monitor undo-space growth and query latency with production-shaped workloads.
  • Flashback is a targeted recovery tool, not a replacement for backups, binlogs, or tested disaster-recovery procedures.

Alibaba Cloud RDS MySQL

RDS MySQL also provides Native Flashback, with managed enablement and retention settings. See the official English documentation and Chinese documentation.

RDS versions, console operations, and parameter policy are product-specific. For a source build, use the startup rules, defaults, ranges, and SQL restrictions on this page.