txn to pss ratio

Summary information

Default value

16

Valid values

1 to 2147483647

Status

Static

Display level

1

Required role

System Administrator

Adaptive Server manages transactions as configurable server resources. Each time a new transaction begins, Adaptive Server must obtain a free transaction descriptor from a global pool that is created at boot time. Transaction descriptors are internal memory structures that Adaptive Server uses to represent active transactions.

Adaptive Server requires one free transaction descriptor for:

txn to pss ratio determines the total number of transaction descriptors available to the server. At start-up, this ratio is multiplied by the number of PSS structures to create the transaction descriptor pool:

# of transaction descriptors = PSS structures * txn to pss ratio

The default value, 16, ensures compatibility with earlier versions of Adaptive Server. Prior to version 12.x, Adaptive Server allocated 16 transaction descriptors for each user connection. In version 12.x and later, the number of simultaneous transactions is limited only by the number of transaction descriptors available in the server.

NoteYou can have as many databases in a user transaction as there are in your Adaptive Server installation. For example, if your Adaptive Server has 25 databases, you can include 25 databases in your user transactions.


Optimizing the txn to pss ratio for your system

During a peak period, use sp_monitorconfig to examine the use of transaction descriptors:

sp_monitorconfig "txn to pss ratio"
Usage information at date and time: Apr 22 2002  2:49PM.
Name               num_free  num_active   pct_act    Max_Used   Reused
--------------     --------  ----------  ---------   --------   ------
txn to pss ratio   784       80          10.20       523        NA

If the #Free value is zero or very low, transactions may be delayed as Adaptive Server waits for transaction descriptors to become free in the server. In this case, you should consider increasing the value of txn to pss ratio.

If the #Max Ever Used value is too low, unused transaction descriptors may be consuming memory that can be used by other server functions. Consider reducing the value of txn to pss ratio.