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InfoQ Homepage News Google Cloud Spanner Introduces Configurable Read-Only Replicas and Zero-Downtime Move Service

Google Cloud Spanner Introduces Configurable Read-Only Replicas and Zero-Downtime Move Service

Google recently announced new regional and multi-regional capabilities for Cloud Spanner. The distributed SQL database now supports configurable read-only replicas and introduced a "zero-downtime" instance move service.

Cloud Spanner supports regional and multi-regional configurations, with regional configurations providing 99.99% availability and multi-regional configurations, providing 99.999% availability and protection from regional outages. But low latency was hard to achieve globally as Mark Donsky, senior product manager, explains:

Until today, read-only replicas were available in several multi-region configurations: nam6, nam9, nam12, nam-eur-asia1, and nam-eur-asia3. But now, with configurable read-only replicas, you can add read-only replicas to any regional or multi-regional Spanner instance so that you can deliver low-latency stale reads to clients everywhere.

Cloud Spanner offers three types of replicas: read-write replicas, read-only replicas, and witness replicas. Read-only replicas provide low-latency stale reads to nearby clients and help increase a node’s read scalability. As they do not participate in voting to commit writes, the read-only replicas do not contribute to the write latency.

The zero-downtime instance move service is designed to move production Spanner instances from any configuration and region to a different one, without downtime, supporting regional, multi-regional, and custom deployments with configurable read-only replicas. Donsky highlights the previous challenge:

So you can imagine that moving a Spanner instance from one configuration to another — say us-central1 in Iowa to nam3 with a read-only replica in us-west2 — is no small feat. Factor in Spanner’s stringent availability of up to 99.999% while serving traffic at an extreme scale, and it might seem impossible to move a Spanner instance from us-central1 to nam3 with zero downtime.

The combination of the new service and the option to customize configurations with additional read replicas now allows customers to move an instance to a different location on Google Cloud. Depending on the environment, the operation might require from a few hours to a few days to complete, but during the process Cloud Spanner maintains high availability and strong consistency, preserving the SLA guarantees.

During the change, both the source and destination instance configurations are subject to hourly compute and storage charges. The new zero-downtime move service requires opening a ticket with Google support and currently has some limitations: moving instances across projects and accounts is not supported, Spanner free trial instances are not supported and an instance must have a minimum of 1 node (1000 processing units).

On a separate announcement, Spanner fine-grained access control is now generally available, allowing database administrators to define database roles, grant privileges to the roles, and create IAM policies to grant permissions on roles to IAM principals. Earlier this year, Spanner introduced support for regional endpoints, where data is stored and processed within the same region to comply with regulatory requirements, but the feature has been rolled back and moved to a future release.

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