How to determine when to reduce physical memory for SQL Server?

Question

If I repeatedly notice SQL Server reporting a lot of free memory, can I likely remove about that amount of memory from the server without affecting performance? Or, can/should it use more for caching?

For this particular example, the server is running SQL Server 2012 Standard Edition on Windows Server 2012. It has 20 GB of physical memory and hosts over 100 GB of data. SQL Server is the only application running on the server.

SQLServer;Buffer Manager
    Buffer cache hit ratio       99.737 %
    Page life expectancy            874 s
SQLServer:Memory Manager
    Database Cache Memory         6,744 MB
    Free Memory                   5,937 MB
    Optimizer Memory                  5 MB
    SQL Cache Memory                 29 MB
    Target Server Memory         19,015 MB
    Total Server Memory          18,407 MB

Answer 1

Your Page life expectancy counter is at 874 seconds. That isn't a lot. I'm guessing that the server isn't configured correctly, or something on the OS is taking the memory. Odds are this server could use more RAM to up the PLE.

Answer 2

If the server performing fine and there are no complains, I will leave this server alone. But, SQL Server tend to use as much memory as possible. Therefore you should check the configuration why the server not using the memory. Run some large queries to see, if the data cache get filled up. If you do not need these memory anywhere else, why would you want to reduce it?

I always use SQL Server Spotlight to diagnose my server. Download a trial version and use it for 30 days to analyze this server, unless you are comfortable with DMVs. I feel like SQL Server does not see your 20 GB of RAM.