System Statistical Functions, Stored Procedures, and the DBCC SQLPERF Command - Microsoft SQL Server 2012 Performance Tuning - page 62

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The following is a list of system statistical functions, along with their descriptions, that you will
find useful in monitoring SQL Server. All these system statistical functions return an aggregate
value that most of them have cumulatively calculated since SQL Server starts or restarts.
Let us briefly discuss all of them one by one and see what they will return:
F @@CONNECTIONS: This function returns an integer value that represents the
number of connections that have been attempted since the SQL Server service was
last started. These connection attempts may either be successful or unsuccessful.
F @@MAX_CONNECTIONS: This function returns an integer value that represents
the number of maximum connections that are allowed simultaneously. The value
depends on the current setting that has been configured for 'Max Connections'
with sp_configure , the version of SQL Server, and also the limitations of
applications and hardware.
F @@TIMETICKS: This function returns an integer value that represents the number of
microseconds that make up a tick. A tick is system-dependent time unit. A tick in an
operating system is generally 31.50 milliseconds.
F @@CPU_BUSY: This function returns an integer value that represents the CPU time
in ticks that SQL Server has taken to perform its tasks since the SQL Server service
was last started. Remember that on machines with multiple processors, this value is
cumulative for all CPUs used by SQL Server.
F @@IDLE: This function returns an integer value that represents the CPU time in ticks
that SQL Server has been idle for, since the SQL Server service was last started.
Remember that on machines with multiple processors, this value is cumulative
for all CPUs used by SQL Server.
F @@IO_BUSY: This function returns an integer value that represents the CPU time
in ticks that SQL Server has taken to perform input/output operations since the
SQL Server service was last started. Remember that on machines with multiple
processors, this value is cumulative for all CPUs used by SQL Server.
F @@PACK_RECEIVED: This function returns an integer value that represents the
total number of network packets that SQL Server has received since the SQL
Server service was last started.
F @@PACK_SENT: This function returns an integer value that represents the total
number of network packets that SQL Server has sent since the SQL Server service
was last started.
F @@PACKET_ERRORS: This function returns an integer value that represents the total
number of erroneous network packets that SQL Server has encountered since the
SQL Server service was last started.
F @@TOTAL_READ: This function returns an integer value that represents the total
number of physical read operations that SQL Server has performed since the SQL
Server service was last started.