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# Oracle performance counters

The following measurements are most commonly used when monitoring the Oracle server (from the V$SYSSTAT table):

Measurement | Description
--- | ---
CPU used by this session | The amount of CPU time (in 10s of milliseconds) used by a session between the time a user call started and ended. Some user calls can be completed within 10 milliseconds and, as a result, the start and end-user call time can be the same. In this case, 0 milliseconds are added to the statistic. A similar problem can exist in the operating system reporting, especially on systems that suffer from many context switches.
Bytes received via SQL*Net from client | The total number of bytes received from the client over Net8.
Logons current | The total number of current logons
Opens of replaced files | The total number of files that needed to be reopened because they were no longer in the process file cache.
User calls | Oracle allocates resources (Call State Objects) to keep track of relevant user call data structures every time you log in, parse, or execute. When determining activity, the ratio of user calls to RPI calls gives you an indication of how much internal work is generated as a result of the type of requests the user is sending to Oracle.
SQL*Net roundtrips to/from client | The total number of Net8 messages sent to, and received from, the client.
Bytes sent via SQL*Net to client | The total number of bytes sent to the client from the foreground process(es).
Opened cursors current | The total number of current open cursors.
DB block changes | Closely related to consistent changes, this statistic counts the total number of changes that were made to all blocks in the SGA that were part of an update or delete operation. These are changes that generate redo log entries, and hence can cause permanent changes to the database if the transaction is committed. This statistic is a rough indication of total database work and indicates (possibly on a per-transaction level) the rate at which buffers are being dirtied.
Total file opens | The total number of file opens being performed by the instance. Each process needs a number of files (control file, log file, database file) to work against the database.

### See also

- Database Server Resource monitoring

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