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Analyzing Memory Requirements for SQL Server


Analyzing Memory Requirements for SQL Server

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Arindam Banerjee
Arindam Banerjee
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Hi Ken,

I did not come to this conclusion only by myself. It came out with a discussion with one of the MVP (SQL Server) Vinod Kumar on a recent Tech-Ed session. I have explained it in the previous post.

Thanks,

~Arindam.


Ravi Prashanth Lobo-275382
Ravi Prashanth Lobo-275382
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Hey, even I have heard about this rule.

This is NOT a hard and fast rule, what it means is - If you have a RAM more than your DB size then increasing the RAM may not help!

Do you also want to know how many DB's I have worked on? ;-)


Marios Philippopoulos
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Does the "Process\Working Set" counter include AWE memory utilization?
I don't think it does.

In my machine it reaches 700,000,000 (700 MB), which is way below the 13.2 GB allocated using AWE.

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Ken Shapley (7/17/2006)


"Generally, the rule of thumb is to have as much as RAM as your data file is."

Did you come up with this rule yourself? How many databases have you worked with in your career?


This does make sense. It may not be feasible with today's technologies and current costs of buying new RAM, but will likely be reality in a few years time. The 64-bit platform was an exotic curiosity a few years back, but not any more.

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Persisting SQL Server Index-Usage Statistics with MERGE
Turbocharge Your Database Maintenance With Service Broker: Part 2
Scott Whigham
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Vladan (7/17/2006)
I am a bit surprised by some things in this article... for example:

"Generally, the rule of thumb is to have as much as RAM as your data file is."


You are right to be "surprised" (I was too). There are so many things peculiar about that statement:

  • What happens when you have a 500GB database?

  • What about when I have 200 50MB databases on my system?

  • What about databases with multiple data files?

  • How does FILESTREAM affect this recommendation?

I understand trying to simplify the planning process and maybe that's what he was going for? You certainly can't hurt having that much RAM but I've never seen that as a recommendation from anyone before.

What we care about is maintaining enough RAM to cover connections, plans, and the buffer cache (generally speaking). Saying that, "the rule of thumb is to have as much as RAM as your data file is" is suggesting that SQL Server will load your entire database in memory and serve it from RAM - which it won't (at least not without you querying/using the actual data).

RAM recommendations need to be done per app+db - OLAP, OLTP, combo. IMO it's hard to guesstimate what an unknown database's memory requirements will be. If you don't tell me how big it is, what it is used for, how it is loaded, how many users there are at launch vs. one year later, etc - I don't know anyone who can accurately provide that info.

I'll give you an example - I asked earlier, "What happens when you have a 500GB database?" Can you estimate the memory requirements for that database? I certainly can't. There are massively different needs depending on how it is used, etc. Maybe you do need 500GB of RAM - I don't have a clue.

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I have about 1,000 video tutorials on SQL Server 2008, 2005, and 2000 over at http://www.learnitfirst.com/Database-Professionals.aspx
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There are more to consider beside the database size. Some time, for the database with small size you can build a query that produced large amount of data. So we have to consider how your store procedure and query are built.
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