You can use the storage usage metric to help you understand your storage costs. For more information about storage usage charges, see Storage and Networking Pricing.

Cloud SQL uses transaction logs for point-in-time recovery (PITR). These logs use storage space, and are deleted automatically with their associated automatic backups. This happens after the value set for transactionLogRetentionDays is met. This value is the number of days of transaction logs that Cloud SQL retains for PITR. You can't delete these logs manually, but you can change the number of days to retain them, from 1 to 35 for Cloud SQL Enterprise Plus edition and 1 to 7 for Cloud SQL Enterprise edition.

For instances that have transaction logs stored in Cloud Storage, the logs are stored in the same region as the primary instance. This log storage (up to seven days, the maximum length for PITR) generates no additional cost per instance.

If the size of your transaction logs is causing an issue for your instance, then increase your storage size. However, the transaction log size increase in the disk usage might be temporary. If your instance has point-in-time recovery enabled, then deactivate and re-enable PITR to ensure that logs are stored in Cloud Storage in the same region as the instance. This deletes the logs, so you can't perform a point-in-time-restore earlier than the time that you re-enabled PITR. However, although the existing logs are deleted, the disk size remains the same.

To avoid unexpected storage issues, we recommend enabling automatic storage increases for all instances when using PITR. This recommendation applies only if your instance has PITR enabled and your logs are stored on disk.

To delete the logs and recover storage, you can deactivate and then re-enable PITR. Decreasing the logs used doesn't shrink the size of the disk provisioned for the instance.

Temp data is included in the storage usage metric. Temp data is removed as part of maintenance and is allowed to increase beyond user-defined capacity limits to avoid a disk full event, at no charge to the user.

Data usage is also included in the storage usage metric. As part of data usage, when a transaction modifies a database, before Cloud SQL modifies the original data, a copy is made of this data. The copy of the data is undo data.

A newly created database uses about 100 MB for system tables and files.

You can use this metric to monitor whether your instance has sufficient CPU for your application needs. If this value is running too high, you can increase the size of your machine type to give your instance more CPU capability.

The amount of memory being used by your instance.

The Number of Reads metric is the number of read operations served from disk that do not come from cache. You can use this metric to help you understand whether your instance is correctly sized for your environment. If needed, you can move to a larger machine type to serve more requests from cache and reduce latency.

The Number of Writes metric is the number of write operations to disk. Write activity is generated even if your application is not active, because Cloud SQL instances write to a system table approximately every second (except for replicas).