Buffer Pool Extension – SQL Server 2014

With SQL Server 2014, Microsoft is bringing a lot of features/enhancements into the wild, one of them is “Buffer Pool Extension” AKA BPE. ( Enterprise edition Only). With RTM, MSFT announced that even Standard edition has this feature.

so, what is BPE?  The name itself is pretty much self explanatory…It’s an extension for your Buffer pool. yes, with this you can use any non volatile storage device(SSD’s preferred) as an extension for your SQL Server Buffer Pool. Basic idea here is to eliminate requirement of “adding more physical RAM”, Instead you can mount a new Drive and tell SQL Server to treat that newly created drive as Buffer Pool. Sounds very interesting right? But there are few limitations Per Microsoft SQL Server Team’s Blog which we should keep in mind.

Limitations:
Enterprise Only Feature.
Might not be useful for OLAP/DSS Work loads.
Even in OLTP workloads, improvements are very limited for Write-heavy work loads.
If your server got more than 64 GB of RAM, don’t expect much from this.

Personally, for me these limitations are really frustrating. On one hand, this is Enterprise only feature and on the other hand, they are saying don’t expect much from this if your SQL Server has got already more than 64 GB of RAM allocated. What are the chances, any DBA would build a new SQL Server 2014(Enterprise) with less than or equal to 64 Gigs in 2014 or 2015? I would say almost “NIL”.

It Offers:
Performance Gain on Read heavy OLTP Work Loads.

MSFT recommendations:  (From SQL Server team Blog post)
Use High throughput SSD for better results.
Start from 4x-10x of the Memory available to SQL Server.

How to Enable BPE :
Step 1:
I’ve created a new Drive(BPE) for this demo purpose as shown below.

1

Step 2:
Before enabling BPE, Let’s check max memory setting I’ve got on this Instance.(512 MB as shown below)

2

Step 3: 
I’ve tried enabling BPE with 500 MB which actually failed. Reason – Buffer Pool extension size must be larger than current memory allocation threshold.(See below screenshot)

3

Well, now I increased the size to 600MB and now I got a different Error message(See below)!

4

Am not sure why this happened, but I’ve created a new Drive (F$) with 2 GB size and it worked this time without any issues as you can see below!!!…I will investigate further why this happened some time later.

5

6

Examine from DMV:

7

How to disable BPE: 

8

Can We alter the size of BPE?
Nope, we can’t. We have to basically disable and recreate it with new size.

Caution: When you disable BPE, chances are….you will get into significant Memory Pressure situation  and hence  increased IO Pressure.

Bottom line: IMHO, this idea sounds interesting, but I don’t think I would implement this on a production SQL Server considering the limitations it has(YMMV). I would rather convince  my management for purchasing real Memory which has no hand cuffs and no limitations!

After all….What are the chances my client doesn’t have money to purchase more DRAM for the sake of true performance boost when they’ve enough money to purchase High Performance SSD’s just for the sake of BPE(which promises me only limited performance gains)? . Remember folks…..now a days physical RAM is very cheap.

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