How multiple instances shares CPU and Memory ?

• Joy Smith San

  SSC-Insane

  Points: 24877

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  January 29, 2015 at 7:11 pm

  #300663

  Hi,

  We have a SQL Server 2008 installed on one server. It has 2 CPUs and 8 GB Ram (6 GB allocated to SQL)

  DBs are small and is working fine.

  Now due to some reasons, we want to comobine another application DBs in this server.

  No more CPU and Memory will be added to server.

  I was planning to add a seperate instance for this different application.

  I install one more instance, how the CPU and Memory will be shared between these 2 instances ?

  Can someone guide me if it's better to host all DBs in single existing instance, or to have a new instance for the new application ?

  Thanks,

  San.

• lmarkum

  SSCertifiable

  Points: 7989

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  January 29, 2015 at 9:05 pm

  #1774229

  Joy Smith San (1/29/2015)

  ---

  Hi,

  We have a SQL Server 2008 installed on one server. It has 2 CPUs and 8 GB Ram (6 GB allocated to SQL)

  DBs are small and is working fine.

  Now due to some reasons, we want to comobine another application DBs in this server.

  No more CPU and Memory will be added to server.

  I was planning to add a seperate instance for this different application.

  I install one more instance, how the CPU and Memory will be shared between these 2 instances ?

  Can someone guide me if it's better to host all DBs in single existing instance, or to have a new instance for the new application ?

  Thanks,

  San.

  With that small amount of RAM I would encourage you not to install a second instance of SQL Server. My reasoning is this. A second install will, at minimum, require a separate instance of the database engine service. You will be needlessly taxing your memory to run a second instance. Also, let's say later that you want to install SSRS. Now you are adding another service to a machine with only 2 GB left for the OS and every other process that needs to run, which would include the SSRS service as the 6 GB you have allocated to SQL Server is for the buffer pool of the database engine.

  I would actually be surprised if you are not already putting memory pressure on the machine by leaving it with only 2GB of RAM for the OS and other processes. I would definitely look at some perfmon and SQL Server counters related to memory management and see what the performance is like. This may very well give you the leverage you need to persuade someone to buy more RAM.