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TiFlash Upgrade Guide

This document describes the function changes and recommended actions that you need to learn when you upgrade TiFlash.

To learn the standard upgrade process, see the following documents:

From 5.x or v6.0 to v6.1

When you upgrade TiFlash from v5.x or v6.0 to v6.1, pay attention to the functional changes in TiFlash Proxy and dynamic pruning.

TiFlash Proxy

TiFlash Proxy is upgraded in v6.1.0 (aligned with TiKV v6.0.0). The new version has upgraded the RocksDB version. After you upgrade TiFlash to v6.1, the data format is converted to the new version automatically.

In regular upgrades, the data conversion does not involve any risks. However, if you need to downgrade TiFlash from v6.1 to any earlier version in special scenarios (for example, testing or verification scenarios), the earlier version might fail to parse the new RocksDB configuration. As as result, TiFlash will fail to restart. It is recommended that you fully test and verify the upgrade process and prepare an emergency plan.

Workaround for downgrading TiFlash in testing or other special scenarios

You can forcibly scale in the target TiFlash node and then replicate data from TiKV again. For detailed steps, see Scale in a TiFlash cluster.

Dynamic pruning

If you do not enable dynamic pruning mode and will not use it in the future, you can skip this section.

  • Newly installed TiDB v6.1.0: Dynamic pruning is enabled by default.

  • TiDB v6.0 and earlier: Dynamic pruning is disabled by default. The setting of dynamic pruning after an upgrade inherits that of the previous version. That is, dynamic pruning will not be enabled (or disabled) automatically after an upgrade.

    After an upgrade, to enable dynamic pruning, set tidb_partition_prune_mode to dynamic and manually update GlobalStats of partitioned tables. For details, see Dynamic pruning mode.

From v5.x or v6.0 to v6.2

In TiDB v6.2, TiFlash upgrades its data storage format to the V3 version. Therefore, when you upgrade TiFlash from v5.x or v6.0 to v6.2, besides functional changes in TiFlash Proxy and Dynamic pruning, you also need to pay attention to the functional change in PageStorage.

PageStorage

By default, TiFlash v6.2.0 uses PageStorage V3 version format_version = 4. This new data format significantly reduces the peak write I/O traffic. In scenarios with high update traffic and high concurrency or heavy queries, it effectively relieves excessive CPU usage caused by TiFlash data GC. Meanwhile, compared with the earlier storage format, the V3 version significantly reduces space amplification and resource consumption.

  • After an upgrade to v6.2.0, as new data is written to the existing TiFlash nodes, earlier data will be gradually converted to the new format.

  • However, earlier data cannot be completely converted to the new format during the upgrade, because the conversion consumes a certain amount of system overhead (services are not affected, but you still need to pay attention). After the upgrade, it is recommended that you run the Compact command to convert the data to the new format. The steps are as follows:

    1. Run the following command for each table containing TiFlash replicas:

      ALTER TABLE <table_name> COMPACT tiflash replica;

    2. Restart the TiFlash node.

You can check whether tables still use the old data format on Grafana: TiFlash-Summary > Storage Pool > Storage Pool Run Mode.

  • Only V2: Number of tables using PageStorage V2 (including partitions)
  • Only V3: Number of tables using PageStorage V3 (including partitions)
  • Mix Mode: Number of tables with data format converted from PageStorage V2 to PageStorage V3 (including partitions)

Workaround for downgrading TiFlash in testing or other special scenarios

You can forcibly scale in the target TiFlash node and then replicate data from TiKV again. For detailed steps, see Scale in a TiFlash cluster.

From v6.1 to v6.2

When you upgrade TiFlash from v6.1 to v6.2, pay attention to the change in data storage format. For details, see PageStorage.

From v6.x or v7.x to v7.3 with storage.format_version = 5 configured

Starting from v7.3, TiFlash introduces a new DTFile version: DTFile V3 (experimental). This new DTFile version can merge multiple small files into a single larger file to reduce the total number of files. In v7.3, the default DTFile version is still V2. To use V3, you can set the TiFlash configuration parameter storage.format_version = 5. After the setting, TiFlash can still read V2 DTFiles and will gradually rewrite existing V2 DTFiles to V3 DTFiles during subsequent data compaction.

After upgrading TiFlash to v7.3 and configuring TiFlash to use V3 DTFiles, if you need to revert TiFlash to an earlier version, you can use the DTTool offline to rewrite V3 DTFiles back to V2 DTFiles. For more information, see DTTool Migration Tool.

From v6.x or v7.x to v7.4 or a later version

Starting from v7.4, to reduce the read and write amplification generated during data compaction, TiFlash optimizes the data compaction logic of PageStorage V3, which leads to changes to some of the underlying storage file names. Therefore, after the upgrade to v7.4 or a later version, in-place downgrading to the original version is not supported.

Workaround for downgrading TiFlash in testing or other special scenarios

To downgrade TiFlash in testing or other special scenarios, you can forcibly scale in the target TiFlash node and then replicate data from TiKV again. For detailed steps, see Scale in a TiFlash cluster.

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