Aaron Bertrand

Memory Limits in SQL Server 2016 SP1

December 12, 2016 by in SQL Server 2016 | 11 Comments
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A few weeks ago, I made a pretty big deal about SQL Server 2016 Service Pack 1. Many features previously reserved for Enterprise Edition were unleashed to lower editions, and I was ecstatic to learn about these changes.

Nonetheless, I'm seeing a few people who are, let's say, a bit less excited than I am.

It's important to keep in mind that the changes here weren't meant to provide complete feature parity across all editions; they were for the specific purpose of creating a more consistent programming surface area. Now customers can use features like In-Memory OLTP, ColumnStore, and compression without worrying about the targeted edition(s) – only about how well they will scale. Several security features that didn't really seem to have anything to do with edition are opened up as well. The one I understood the least was Always Encrypted; I couldn't fathom why only Enterprise customers needed to protect things like credit card data. Transparent Data Encryption is still Enterprise-only, because this isn't really a programmability feature (either it's on or it's not).

So what's really in it for Standard Edition customers?

I think the biggest problem most people have is that max memory in Standard Edition is still limited to 128GB. They look at that and say, "Gee, thanks for all the features, but the memory limit means I can't really use them."

However, the surface area changes bring about performance improvement opportunities, even if that wasn't their original intention (or even if it was – I wasn't in any of those meetings). Let's take a closer look at a small section of the fine print (from the official docs):

Memory limits for Enterprise/Standard in 2016 SP1Memory limits for Enterprise/Standard in SQL Server 2016 SP1

The astute reader will notice that the buffer pool limit wording has changed, from:

Memory: Maximum memory utilized per instance

To:

Memory: Maximum buffer pool size per instance

This is a better description of what really happens in Standard Edition: a 128GB limit for the buffer pool only, and other memory reservations can be over and above that (think pools like the plan cache). So, in effect, a Standard Edition server could use 128GB of buffer pool, then max server memory could be higher and support more memory used for other reservations. Similarly, Express Edition is now properly documented to use 1.4GB for the buffer pool.

You might also notice some very specific wording in that left-most column (e.g. "per instance" and "per database") for the features that are being exposed in Standard Edition for the first time. To be more specific:

  • The instance is limited to 128GB of memory for the buffer pool.
  • The instance can have an additional  32GB allocated to ColumnStore objects, over and above the buffer pool limit.
  • Each user database on the instance can have an additional  32GB allocated to memory-optimized tables, over and above the buffer pool limit.

And to be crystal clear: These memory limits for ColumnStore and In-Memory OLTP are NOT subtracted from the buffer pool limit, as long as the server has more than 128GB of memory available. If the server has less than 128GB, you will see these technologies compete with buffer pool memory, and in fact be limited to a % of max server memory. More details are available in this post from Microsoft's Parikshit Savjani.

I don't have hardware handy to test the extent of this, but if you had a machine with 256GB or 512GB of memory, you could theoretically use it all with a single Standard Edition instance, if you could – for example – spread your In-Memory data across databases in <= 32GB chunks, for a total of 128GB + (32GB * (# of databases)). If you wanted to use ColumnStore instead of In-Memory, you could spread your data across multiple instances, giving you (128GB + 32GB) * (# of instances). And you could combine these strategies for ((128GB + 32GB ColumnStore) * (# of instances)) + (32GB In-Memory * (# of databases * # of instances)).

Whether breaking your data up in this way is practical for your application, I'm not sure; I'm only suggesting it's possible. Some of you might already be doing some of these things to get better usage out of Standard Edition on servers with more than 128GB of memory.

With ColumnStore specifically, in addition to being allowed to use 32GB in addition to the buffer pool, keep in mind that the compression you can get here means you can often fit a lot more into that 32GB limit than you could with the same data in traditional row-store. And if you can't use ColumnStore for whatever reason (or it still won't fit into 32GB), you can now implement traditional page or row compression – this might not allow you to fit your entire database into the 128GB buffer pool, but it might enable more of your data to be in memory at any given time.

Similar things are possible in Express (at a lower scale), where you can have 1.4GB for buffer pool, but an additional ~352MB per instance for ColumnStore, and ~352MB per database for In-Memory OLTP.

But Enterprise Edition still has lots of upside

There are many other differentiators to keep interest in Enterprise Edition, aside from unlimited memory limits all around – from online rebuilds and merry-go-round scans to full-on Availability Groups and all the virtualization rights you can shake a stick at. Even ColumnStore indexes have well-defined performance enhancements reserved for Enterprise Edition.

So just because there are some techniques that will allow you to get more out of Standard Edition, that does not mean it will magically scale to meet your performance needs. Like my other posts about "doing it on a budget" (e.g. partitioning and readable secondaries), you can certainly spend time and effort kludging together a solution, but it will only get you so far. The point of this post was simply to demonstrate that you can get farther with Standard Edition in 2016 SP1 than you ever could before.