Database Cluster
This functionality is available starting with Shopware 6.4.12.0.
To scale Shopware even further, we recommend to use a database cluster. A database cluster consists of multiple read-only servers that are managed by a single primary instance.
Shopware already splits read and write SQL queries by default. When a write INSERT/UPDATE/DELETE/... query is executed, the query is delegated to the primary server and the current connection uses only the primary node for subsequent calls. This is ensured by the executeStatement method in the DebugStack decoration. That way, Shopware can ensure read-write consistency for records within the same request. However, it doesn't take into account that read-only child nodes might not be in sync with the primary node. This is left to the database replication process.

Preparing Shopware

We suggest following the steps below to make the splitting most effective.

Using the optimal MySQL configuration

By default, Shopware does not set specific MySQL configurations that make sure the database is optimized for the Shopware usage. These variables are set in the cluster mode only on the read-only server. To make sure that Shopware works flawlessly these configuration must be configured directly on the MySQL server so these variables are set on any server.
The following options should be set:
  • Make sure that group_concat_max_len is by default higher or equal to 320000
  • Make sure that sql_mode doesn't contain ONLY_FULL_GROUP_BY
After this change, you can set also SQL_SET_DEFAULT_SESSION_VARIABLES=0 in the .env file so Shopware does not check for those variables at runtime.

Cart in Redis

As we learned in the beginning, Shopware queries a read-only MySQL server until the first write attempt. To maximize this behaviour it is highly recommended to outsource as many write operations as possible from the database. One of the easiest solutions is to use the Redis as storage for store carts. To use Redis, add the following snippet to config/packages/cart.yml
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shopware:
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cart:
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redis_url: 'redis://localhost:6379/0?persistent=1'
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It is recommended to use a persistent Redis connection to avoid connection issues in high load scenarios. There is also a cart:migrate command to migrate the existing carts between MySQL and Redis so the migration does not influence end user experience.

Configure the Database Cluster

To use the MySQL Cluster, you have to configure the following in the .env file:
  • DATABASE_URL is the connection string for the MySQL primary.
  • DATABASE_REPLICA_x_URL (e.g DATABASE_REPLICA_0_URL, DATABASE_REPLICA_1_URL) - is the connection string for the MySQL read-only server.