Shulou(Shulou.com)06/01 Report--

New features and enhancements in AlwaysOn 2017

Some new features and enhancements to AlwaysOn 2017:

L availability group parameter configuration: minimum number of submitted secondary copies (REQUIRED_COPIES_TO_COMMIT)

L read scale availability group (Read-scale availability groups)

Availability groups on Linux

Failover cluster instance on l Linux

L cross-platform availability groups

Availability group parameter configuration: minimum number of submitted secondary copies (REQUIRED_COPIES_TO_COMMIT)

CREATE AVAILABILITY GROUP [ag1] WITH (REQUIRED_COPIES_TO_COMMIT = 1)

Let the user configure the minimum number of copies that need to be committed before the transaction is committed on the master copy. Make sure the transaction waits until the transaction log is updated on the minimum secondary copy. The default value is 0, and the maximum value is the number of copies minus 1 (the related copy must be in synchronous commit mode). Typically, if the SQL server that hosts the secondary synchronous copy stops responding, the primary copy marks the secondary copy as out of sync and continues. When the unresponsive database comes back online, it will be in the "out of sync" state, and the copy will be marked as abnormal until the master can synchronize it again. If the minimum number of copies is not available, the commit on the master copy will fail. ALTER AVAILABILITY GROUP supports REQUIRED_COPIES_TO_COMMIT.

Read scale availability group (Read-scale availability groups)

In SQL Server 2016 and earlier, clustering is required for all availability groups. Clusters are used to provide business continuity, high availability, and disaster recovery (HADR). In addition, the secondary copy is configured to perform the read operation. If the goal is not high availability, configuring and running the cluster consumes considerable operational overhead. SQL Server 2017 introduces read scaling availability groups that do not require clustering.

If the business requirement is to convert resources for mission-critical workloads running on the primary copy, users can now use read-only routing or connect directly to the readable secondary copy. Without having to rely on integration with any cluster technology. SQL Server 2017 on Windows and Linux platforms supports these new features.

This is not a high availability configuration. There is no need to monitor infrastructure, coordinate fault detection, and perform automatic failover. Without clustering, SQL Server cannot provide the low recovery time goal (RTO) that an automated high availability solution can provide. If high availability is required, use Cluster Administrator (Windows Server failover cluster on Windows or Pacemaker on Linux).

Reading the scaling availability group provides disaster recovery capabilities. The recovery point objective (RPO) 0 is provided when the read-only copy is in synchronous commit mode. "to fail over a read scale availability group, see fail over the primary copy on a read scale availability group."

In general, this feature has only DR functionality and does not support HA. This feature applies only to the deployment of multiple read-only copies on multiple servers to share the read pressure.

Solutions in different geographic locations can use distributed availability groups to implement read scaling solutions. This can be used to reduce the read workload of primary copies, readable secondary copies, and sites close to the read workload source.

Reference:

Https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/read-scale-availability-groups

Https://blogs.msdn.microsoft.com/sql_pfe_blog/2017/11/17/sql-server-2017-read-scale-availability-groups/

Configure read scaling availability groups on Linux

Availability groups on Linux

Configuring AG on Linux is based on cluster Pacemaker and quorum Corosync

Reference:

Https://docs.microsoft.com/en-us/sql/linux/sql-server-linux-availability-group-overview

Failover Cluster instance on Linux

Configuring FCI official documentation on Linux is still crude, and from a shared storage point of view, it currently supports iSCSI, NFS, and SMB protocols.

Reference:

Https://docs.microsoft.com/en-us/sql/linux/sql-server-linux-shared-disk-cluster-concepts

Cross-platform availability group

This configuration does not support high availability because there is no clustering solution to manage cross-platform configurations. Creating one copy on Windows server and other replicas on the Linux server is always a step in the availability group (AG). This configuration is cross-platform because the copies are on different operating systems. Migrate to another platform or use this configuration for disaster recovery (DR).

Reference:

Https://docs.microsoft.com/en-us/sql/linux/sql-server-linux-availability-group-cross-platform?view=sql-server-2017&viewFallbackFrom=sql-server-linux-2017

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