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how many extra RAM for SQL server is needed

hi,

I read all that:

https://www.sqlpassion.at/archive/2016/09/19/how-much-ram-do-i-need-for-sql-server/?awt_l=FjEA6&awt_m=3Vt_2eQyB6YUUTS
https://www.sqlskills.com/blogs/jonathan/how-much-memory-does-my-sql-server-actually-need/

none of them are telling me how much MORE RAM we need for the SQL server.

I am measuring a SQL server box which is a publisher and distributor, the more replication we create the more RAM contention we have.

but how to measure/calculate HOW MUCH RAM we still need?
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marrowyung
Asked:
marrowyung
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Pawan KumarDatabase ExpertCommented:
Basically it depends on the workload & requirement of your system.

Have you gone through the Brent Ozar blog. He is very good with hardware stuff. few links for your help.

https://www.brentozar.com/archive/2014/05/much-memory-sql-server-need/

https://sqlperformance.com/2013/10/sql-memory/how-much-ram

https://technet.microsoft.com/en-us/library/cc298801.aspx

Enjoy!!
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Pawan KumarDatabase ExpertCommented:
Let's take an example. If we have total of 80GB of database then we don't need 64GB of RAM. So we need to make assumtion like how much % of the entire database is going to be in use at a time.

In most of the OLTP cases we use about 15-20% of the entire DB at a time.
A BI system may use about 60% of the entire DB at a time.

So What kind of System we are developing and What's the workload are very important to start with.
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marrowyungSenior Technical architecture (Data)Author Commented:
nono, there are no calculation + performance counter to measure that out
?


boss can simply ask, how much RAM extra I need ?

actually this one don't tell much as it is more on Sharepoint deployment and planning.

Or only this one is useful:

Memory: Pages/sec   This counter shows the rate at which pages are read from or written to disk to resolve hard page faults. Monitor this counter to make sure that it remains under 100.
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Pawan KumarDatabase ExpertCommented:
I will tell you before that can you tell what kind of system we are developing ?

OLTP / OLAP - Tabular / Mutildimensional ?
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marrowyungSenior Technical architecture (Data)Author Commented:
just normal transaction database.

Mutildimensional usually but we don't actually use most of it.

I am measuring pages/sec, page life expectancy. % disk read time, % disk write time.
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Pawan KumarDatabase ExpertCommented:
Can you also tell me the size of DB ?
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marrowyungSenior Technical architecture (Data)Author Commented:
831 GB. we are using SQL 2008 with SP3 and we can't use in-memory tech.
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Pawan KumarDatabase ExpertCommented:
Okies so in my opinion you should go with 96GB of Ram.

Note that it depends on lot of factors. This is just an estimate.
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marrowyungSenior Technical architecture (Data)Author Commented:
this is the problem, we are running 64GB of RAM now, how you comes up with 96GB of RAM?

the SQL box is both publisher and distributor. any rules by saying how much RAM per publication need ?
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Pawan KumarDatabase ExpertCommented:
Okay , so upgrade to 96GB first. :) Details below-

At one time you need around 45 GB of  Data in RAM , which is 20 % of the overall DB size we have.

Now we should max given 50% of the RAM for SQL DB Engine. So effectively we need to double the RAM.

In your case it comes out to 90. and 96 is the closest, that's why I choose it.
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marrowyungSenior Technical architecture (Data)Author Commented:
"At one time you need around 45 GB of  Data in RAM "

we have 831 GB database size, why 45GB? I think it is 166GB.

"Now we should max given 50% of the RAM for SQL DB Engine. So effectively we need to double the RAM."

why 50% ?
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Pawan KumarDatabase ExpertCommented:

"Now we should max given 50% of the RAM for SQL DB Engine. So effectively we need to double the RAM."

You have define what max ram you want to give to SQL Server out of the total RAM available for the entire machine , You must provide RAM for other processes also like Operating System , office,,etc  

"At one time you need around 45 GB of  Data in RAM "we have 831 GB database size, why 45GB? I think it is 166GB.

Yes you are write, that is a typo.
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marrowyungSenior Technical architecture (Data)Author Commented:
so it is not 96GB of RAM, right? I have to proof that this is exactly what we need to add.

and also how much RAM extra each additional replication/publication need?
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Pawan KumarDatabase ExpertCommented:
No we need 96 GB only. Additional how much need for replication I need to check.
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marrowyungSenior Technical architecture (Data)Author Commented:
"Additional how much need for replication I need to check."

tks.

a calculate with all variable you discussed is preferrable, like database size is a varible , which make your conclusion of 96GB of RAM with link to proof is perfect.

"No we need 96 GB only"

I don't know what make this figure comes out is needed, tks.
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Pawan KumarDatabase ExpertCommented:
there is no Maths around this.  We just have to decide based on our requirement and later on increase the hardware when the load grows.
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marrowyungSenior Technical architecture (Data)Author Commented:
"We just have to decide based on our requirement "

what requirement ? if I tell my boss says for each publication we need extra 20B of RAM because of ......., then it is much better.

we add one more publication it will use RAM again.

"and later on increase the hardware when the load grows."

what if during the weekend we will see unresponsive replication agent error message or long running replication error message. usually we see it during the weekend only. so can't add RAM because of load grows.

we need time to order it.

and I saw before that publisher shows replication tempdb contention and a lot of time this replication agent log gone without any reason.

any tools you can suggest me to use to detect if there are ?

I knew there are tempdb speed measurement on write speed latency, but for replication ,how can we measure we need to do sth on the tempdb.
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Pawan KumarDatabase ExpertCommented:
Well there are many tools available in the market. There are many good from redgate.

http://www.red-gate.com/products/

Other tools to check performance are -

Database health monitoring <<http://databasehealth.com/>>.
Cloudmonix.  <<http://cloudmonix.com/blog/the-ultimate-list-of-top-sql-monitoring-tools/>>

I have not tried these. Freeware or not - verify. You may be need try out few and choose based on your need.
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marrowyungSenior Technical architecture (Data)Author Commented:
then forget about it, I will tried to make use of the idera DM for that.
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Pawan KumarDatabase ExpertCommented:
No problem. If Idera works for you then it is great.
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marrowyungSenior Technical architecture (Data)Author Commented:
I am using this guideline for that:

https://www.brentozar.com/archive/2013/09/how-to-prove-your-sql-server-needs-more-memory-video/

and it seems publisher still have just enough RAM.

let see what will be told by DM.
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marrowyungSenior Technical architecture (Data)Author Commented:
tks.
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marrowyungSenior Technical architecture (Data)Author Commented:
hi,

I re read that it seems no fixed calculation on how much RAM we need further for our SQL server?

and this one: https://www.brentozar.com/archive/2014/05/much-memory-sql-server-need/

don't even tell us at all, it just say need more RAM but how much RAM ?  I am happy if there are a performance counter check this.
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