SQL Server, RAM Usage, Networking Admin

Question

We have a VM Guest configured as follows: dedicated Sql 2008  Sp3 (x64) running on Windows 2008 R2 x64, 32GB RAM. Per Task Manager (if it is to be believed) the sql server process has allocated 20GB of RAM. The Networking Manager says
that sql grabs every bit of memory you give it.  He has a hard time believing that sql really needs that much memory.
a. I pointed out that we can cap the (buffer pool) memory and that sql, while reserving it, will not use the RAM unless it is actually needed. (In other words, that 20GB was needed at one point in time).
b. I also pointed out that sql is not too quick to return the memory even it is no longer needed.
c. I look for hard page faults on the server as an initial indication that RAM may be taxed.
d. I told him there is no easy way to estimate the amount of RAM that a given sql server needs 
In your opinion, are the statements a-d relatively factual or way off base?
TIA,
edm2
P.S. Recently he indicated that if we raise the Sql RAM limit on a box then Sql will take it all and, despite, what is commonly said, large amounts of RAM costs lots of money.  Let us say this matter has been a point of contention between us for
some time and we are still on opposite sides of the railroad track.

Answer 1

Hello,
Per Task Manager (if it is to be believed) the sql server process has allocated 20GB of RAM. The Networking Manager says that sql grabs every bit of memory you give it. He has a hard time believing that sql really needs that much memory.
You're correct, don't trust task manager. If the server is not configured (max server memory) then yes, SQL Server will gobble up all available memory if it needs to (it on allocates memory if it already doesn't have room).
a. I pointed out that we can cap the (buffer pool) memory and that sql, while reserving it, will not use the RAM unless it is actually needed. (In other words, that 20GB was needed at one point in time).
You sir are 100% correct!
b. I also pointed out that sql is not too quick to return the memory even it is no longer needed.
Yes and no. SQL Server can and will respond to the windows low memory flag and give back memory if possible (for example, it won't give it back if using locked pages in memory [LPIM]). Low memory is different in versions of windows but it's always around
100 MB which IMHO is way too late. Couple that with the fact it's a VM and it's memory could already be paged out by the host and no one would ever know means a crash could happen.
c. I look for hard page faults on the server as an initial indication that RAM may be taxed.
That would be true for a physical system. While it still sort of is true for a VM, we have no way of knowing if the host has that memory paged which would also cause issues (slowness, etc). Still doesn't hurt to watch though :)
d. I told him there is no easy way to estimate the amount of RAM that a given sql server needs
SQL Server will always happily take as much memory as you give it, to a point. If at one point it used 20 GB that's a good start. SQL Server wants everything to be in memory, because that has the fastest access time. So take into account the sizes of your
databases, any CLR or items that run outside of the database (or are hosted), all of the queries that want to live in cache as well so they only have to be compiled once, etc.
In your opinion, are the statements a-d relatively factual or way off base?
See above :)
P.S. Recently he indicated that if we raise the Sql RAM limit on a box then Sql will take it all and, despite, what is commonly said, large amounts of RAM costs lots of money. Let us say this matter has been a point of contention between us for
some time and we are still on opposite sides of the railroad track.
I feel you. Things to look for inside of SQL Server for memory pressure are lazy writes/second, free list stalls, a large increase in general IO of the server (could just mean the workload changed, tbh), etc. Also, depending on how the Guest is setup and
the Host is configured will have a lot to do with performance. For example, if the guest can cross numa nodes and ends up accessing tons of foreign memory, if dynamic memory for the guest is used and constantly swapped. None of those will manifest itself in
the counters but will surely have a negative impact on SQL Server.
So, to be fair to you, you're correct in that (Depending on how the Host/Guest is configured) adding more RAM may or may not help (or make things worse if the memory is all paged on the host). To be fair to him, SQL Server on a physical box magically makes
things run faster since they'll mostly be in memory.
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