ApsaraDB RDS:Change the size of the InnoDB buffer pool

Prerequisites

Before you begin, ensure that you have:

• An RDS MySQL instance running one of the following editions: RDS High-availability Edition, RDS Basic Edition, or RDS Cluster Edition

Limitations

• Serverless instances: Manual modification of innodb_buffer_pool_size is not supported. Serverless ApsaraDB RDS for MySQL adjusts the buffer pool size automatically when the instance specification changes.

• Out of memory (OOM) risk: Setting the value too large can cause OOM errors and trigger a primary/secondary switchover. Stay within the recommended maximum values in this topic.

When to change the buffer pool size

Increase the buffer pool when server memory is sufficient and you observe high disk I/O under normal load. To check whether your current buffer pool is too small, monitor the Disk Read IOPS metric for your instance in the Monitoring section. If read IOPS is high and unstable under normal load, the working set is likely spilling to disk — consider increasing the buffer pool size. A larger buffer pool also benefits write-heavy workloads: bulk UPDATE statements incur less lock wait and less disk dependency when frequently modified rows stay in memory.

Decrease the buffer pool when memory resources are limited or other applications on the host require more memory.

How the formula works

innodb_buffer_pool_size can only be set using a formula — direct numeric values are not supported. The formula syntax is:

{DBInstanceClassMemory*X/Y}

Example: {DBInstanceClassMemory*7/10} sets the buffer pool to 70% of instance memory.

Adjustable range: [128 MB, DBInstanceClassMemory * 9/10]

• Minimum: 128 MB

• Maximum: 90% of the instance memory available to the database process

Buffer pool capacity rounding

The actual buffer pool size is always a multiple of innodb_buffer_pool_chunk_size × innodb_buffer_pool_instances. If the value you set is not an exact multiple, the system rounds up to the nearest multiple.

• innodb_buffer_pool_chunk_size is fixed at 32 MB. For instances created earlier, it may be 128 MB.

If you set a value that is not a valid multiple, the system adjusts it upward automatically. For example, if innodb_buffer_pool_chunk_size is 1 GB and innodb_buffer_pool_instances is 1, setting innodb_buffer_pool_size to 1.5 GB results in an actual value of 2 GB.

Default and recommended values

(instance memory - system reserved memory) * 3/4

min(instance memory / 2, 2048) + max(instance CPU * 64, instance memory / 64) + (instance memory / 64) + 285

Change the buffer pool size for a single instance

1. Go to the Instances page. In the top navigation bar, select the region where your RDS instance resides. Find the instance and click its ID.

2. In the left-side navigation pane, click Parameters.

3. Find innodb_buffer_pool_size, click to edit the value, and then click OK.

4. Click Submit Parameters, and then click OK in the confirmation dialog box.

Modifying innodb_buffer_pool_size requires a restart for RDS MySQL 5.6. For RDS MySQL 5.7 and 8.0, no restart is required.

Change the buffer pool size for multiple instances

Create a parameter template containing the innodb_buffer_pool_size parameter and apply it to the target instances. If you already have a template with this parameter, update the value in the template and apply it to multiple instances at once.

For details, see Use parameter templates.

What's next

After adjusting innodb_buffer_pool_size, monitor your instance to verify the change is working as expected:

• Use monitoring to check Disk Read IOPS — a sustained drop indicates the working set is now fitting in memory.

• Review slow query logs to identify queries that may still be causing excessive disk reads.

• If memory pressure increases after the change, see troubleshoot memory consumption issues for guidance.