TiDB 3.0 Upgrade Guide

This document is targeted for users who want to upgrade from TiDB 2.0 (2.0.1 or later versions) or TiDB 2.1 RC to TiDB 3.0. TiDB 3.0 is compatible with TiDB Binlog of Kafka Version and TiDB Binlog of Cluster Version.

Upgrade caveat

Rolling back to 2.1.x or earlier versions after upgrading is not supported.
Before upgrading to 3.0 from 2.0.6 or earlier versions, check if there are any running DDL operations, especially time-consuming ones like Add Index. If there are any, wait for the DDL operations to finish before you upgrade.
Parallel DDL is supported in TiDB 2.1 and later versions. Therefore, for clusters with a TiDB version earlier than 2.0.1, rolling update to TiDB 2.1 is not supported. To upgrade, you can choose either of the following two options:
- Stop the cluster and upgrade to 3.0 directly.
- Roll update to 2.0.1 or later 2.0.x versions, and then roll update to the 3.0 version.

Note:

Do not execute any DDL statements during the upgrading process, otherwise the undefined behavior error might occur.

Step 1: Install Ansible and dependencies on the Control Machine

Note:

If you have installed Ansible and its dependencies, you can skip this step.

TiDB Ansible release-3.0 depends on Ansible 2.4.2 and later versions (ansible>=2.4.2, Ansible 2.7.11 recommended) and the Python modules of jinja2>=2.9.6 and jmespath>=0.9.0.

To make it easy to manage dependencies, use pip to install Ansible and its dependencies. For details, see Install Ansible and its dependencies on the Control Machine. For offline environment, see Install Ansible and its dependencies offline on the Control Machine.

After the installation is finished, you can view the version information using the following command:

ansible --version

ansible 2.7.11

pip show jinja2

Name: Jinja2
Version: 2.10

pip show jmespath

Name: jmespath
Version: 0.9.0

Note:

You must install Ansible and its dependencies following the above procedures.

Make sure that the Jinja2 version is correct, otherwise an error occurs when you start Grafana.

Make sure that the jmespath version is correct, otherwise an error occurs when you perform a rolling update to TiKV.

Step 2: Download TiDB Ansible to the Control Machine

Log in to the Control Machine using the tidb user account and enter the /home/tidb directory.
Back up the tidb-ansible folders of TiDB 2.0 or TiDB 2.1 versions using the following command:
```
$ mv tidb-ansible tidb-ansible-bak
```
Download the tidb-ansible with the tag corresponding to TiDB 3.0. For more details, See Download TiDB Ansible to the Control Machine. The default folder name is tidb-ansible.
```
git clone -b $tag https://github.com/pingcap/tidb-ansible.git
```

Step 3: Edit the `inventory.ini` file and the configuration file

Edit the `inventory.ini` file

Edit the inventory.ini file. For IP information, see the /home/tidb/tidb-ansible-bak/inventory.ini backup file.

Note:

Pay special attention to the following variables configuration. For variable meaning, see Description of other variables.

Make sure that ansible_user is the normal user. For unified privilege management, remote installation using the root user is no longer supported. The default configuration uses the tidb user as the SSH remote user and the program running user.
```
## Connection
# ssh via normal user
ansible_user = tidb
```
You can refer to How to configure SSH mutual trust and sudo rules on the Control Machine to automatically configure the mutual trust among hosts.
Keep the process_supervision variable consistent with that in the previous version. It is recommended to use systemd by default.
```
# process supervision, [systemd, supervise]
process_supervision = systemd
```
If you need to modify this variable, see How to modify the supervision method of a process from supervise to systemd. Before you upgrade, first use the /home/tidb/tidb-ansible-bak/ backup branch to modify the supervision method of a process.

Edit the configuration file of TiDB cluster components

If you have previously customized the configuration file of TiDB cluster components, refer to the backup file to modify the corresponding configuration file in the /home/tidb/tidb-ansible/conf directory.

Note the following parameter changes:

In the TiKV configuration, end-point-concurrency is changed to three parameters: high-concurrency, normal-concurrency and low-concurrency.
```
readpool:
  coprocessor:
    # Notice: if CPU_NUM > 8, default thread pool size for coprocessors
    # will be set to CPU_NUM * 0.8.
    # high-concurrency: 8
    # normal-concurrency: 8
    # low-concurrency: 8
```
Note:

For the cluster topology of multiple TiKV instances (processes) on a single machine, you need to modify the three parameters above.

Recommended configuration: the number of TiKV instances * the parameter value = the number of CPU cores * 0.8.
In the TiKV configuration, the block-cache-size parameter of different CFs is changed to block-cache.
```
storage:
  block-cache:
    capacity: "1GB"
```
Note:

For the cluster topology of multiple TiKV instances (processes) on a single machine, you need to modify the capacity parameter.

Recommended configuration: capacity = MEM_TOTAL * 0.5 / the number of TiKV instances.

Step 4: Download TiDB 3.0 binary to the Control Machine

Make sure that tidb_version = v3.0.0 in the tidb-ansible/inventory.ini file, and then run the following command to download TiDB 3.0 binary to the Control Machine:

ansible-playbook local_prepare.yml

Step 5: Perform a rolling update to TiDB cluster components

If the process_supervision variable uses the default systemd parameter, perform a rolling update to the TiDB cluster using excessive_rolling_update.yml.
```
ansible-playbook excessive_rolling_update.yml
```
If the process_supervision variable uses the supervise parameter, perform a rolling update to the TiDB cluster using rolling_update.yml.
```
ansible-playbook rolling_update.yml
```

Note:

To optimize operation and maintenance over TiDB cluster components, the PD service name in the systemd mode is adjusted in TiDB 3.0. After upgrading to TiDB 3.0, you can use rolling_update.yml for both rolling updates and daily rolling restarts. Do not use excessive_rolling_update.yml any longer.

Step 6: Perform a rolling update to TiDB monitoring components

ansible-playbook rolling_update_monitor.yml