# Configuring buffer pool size and redo log capacity in MySQL 8.4
<a name="Appendix.MySQL.CommonDBATasks.Config.Size.8.4"></a>

In MySQL 8.4, Amazon RDS enables the `innodb_dedicated_server` parameter by default. With the `innodb_dedicated_server` parameter, the database engine calculates the `innodb_buffer_pool_size` and `innodb_redo_log_capacity` parameters. For information about how these parameters are calculated, see [Configuring InnoDB Buffer Pool Size](https://dev.mysql.com/doc/refman/8.4/en/innodb-buffer-pool-resize.html) and [Redo Log](https://dev.mysql.com/doc/refman/8.4/en/innodb-redo-log.html) in the MySQL documentation.

With `innodb_dedicated_server` enabled, the `innodb_buffer_pool_size` parameter is calculated based on the DB instance class memory. The following table shows the detected server memory and the corresponding buffer pool size.


| Detected server memory | Buffer pool size | 
| --- | --- | 
|  < 1 GB  |  Default value of 128 MB  | 
|  1 GB to 4 GB  |  *Detected server memory* \$1 0.5  | 
|  > 4 GB  |  *Detected server memory* \$1 0.75  | 

The `innodb_redo_log_capacity` parameter automatically scales with the instance class to (number of vCPUs / 2) GB up to a maximum of 16 GB. Larger instance classes have a larger redo log capacity, which can improve performance and resilience for write-intensive workloads. 

Before upgrading from MySQL 8.0 to MySQL 8.4, be sure to increase your storage space to accommodate a potential increase in the size of the redo logs that might occur after the upgrade completes. For more information, see [Increasing DB instance storage capacity](USER_PIOPS.ModifyingExisting.md).

If you don't want the `innodb_dedicated_server` parameter to calculate the values for the `innodb_buffer_pool_size` and `innodb_redo_log_capacity` parameters, you can override these values by setting specific values for them in a custom parameter group. Alternatively, you can disable the `innodb_dedicated_server` parameter and set values for the `innodb_buffer_pool_size` and `innodb_redo_log_capacity` parameters in a custom parameter group. For more information, see [Default and custom parameter groups](parameter-groups-overview.md#parameter-groups-overview.custom).

If you disable the `innodb_dedicated_server` parameter by setting it to `0` and don't set values for the `innodb_buffer_pool_size` and `innodb_redo_log_capacity` parameters, then Amazon RDS sets the latter two parameters to 128 MB and 100 MB, respectively. These defaults result in poor performance on larger instance classes.