Q           subject

stay Oracle in ,SESSIONS and PROCESSES What is the relationship of ？

     

A           answer          

After the database is installed , It’s often necessary to set SESSIONS and PROCESSES Size . among ,SESSIONS Specifies the number of sessions allowed in an instance , That is, the number of concurrent users who can log in to the database at the same time .PROCESSES Specifies the number of processes that an instance can run simultaneously at the operating system level , Including background process and server process . Because a background process may correspond to two sessions at the same time , therefore , Usually SESSIONS The value of is greater than PROCESSES Value .

By finding official documents , You can know SESSIONS The value of the parameter is Oracle 10g and 11g It’s different , As shown in the following table ：

because SESSIONS The value of is based on PROCESSES It’s calculated from the value of , therefore , In general, you just need to set PROCESSES The value of the can . stay Oracle 11gR2 In the following version ,SESSIONS The formula for calculating the size is ：(1.1 * PROCESSES) + 5; stay Oracle 11gR2 in ,SESSIONS The formula for calculating the size is ：(1.5 * PROCESSES) + 22. if SESSIONS If the current value of is larger than the calculated value , be SESSIONS The value of may remain unchanged ; if SESSIONS If the current value of is smaller than the calculated value , be SESSIONS Take the calculated value , namely SESSIONS The value of is always MAX（ Current value , Calculated value ）, But this is not absolutely .

When the concurrent users of database connection have reached SESSIONS The value of , There’s a new conversation coming in , You’re going to report a mistake “ORA-00018,”maximum number of sessions exceeded”” Error of .

When Oracle Need to start a new PROCESS, And the current number of processes has reached PROCESSES When parameters are , You’re going to report a mistake ：“ORA-00020: maximum number of processes (2048) exceeded”.

If the connection on the database is used up , When a new connection comes , Then it will be generated on the client side “ORA-12519, TNS:no appropriate service handler found” Error message .

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