Can a memory upgrade on Cloud SQL Postgres result in downtime on a highly available system?

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Yes, a memory upgrade on Cloud SQL Postgres can result in downtime on a highly available system. During the upgrade process, the database may need to be temporarily taken offline, which can result in downtime for users. However, Google Cloud provides tools and features to minimize downtime during upgrades, such as automatic failover and replica promotion, that can help reduce the impact on users. It is recommended to plan upgrades during non-peak hours to minimize disruption to users.