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We want to switch an SAP SQL database cluster to SQL Availability Groups. The plan is to have two replica servers in the same data center with synchronous commits, and one in the DR location with Asynchronous commits set.

The concern I have is this database cluster has very high transactions and is always busy. Could we suffer from a performance standpoint?

Is there a way where we can determine if this database will suffer or not based on some metrics we can evaluate beforehand, such as the number of transactions...etc.?

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Could we suffer from a performance standpoint?

In synchronous commit you'll always have a performance hit. How much entirely depends on...

  • Infrastructure (networking latency, bandwidth, distances, etc.)
  • Hardware (server level such as cpu, disk, memory, NIC, drivers)
  • Workload type (single large transactions, tons of tiny, middle of both intermixed)
  • Workload style (constant, bursty, mixed, etc.)

In general, that's I've witnessed anywhere from 3% to 25%.

It's hard to guesstimate due to all of the interactions between various pieces, as such I'd suggest setting up a test environment and trying things there. Regardless, AGs will show you (and run at) the slowest parts (or misconfigured parts) of your setup.

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