Size and Location of the Physical Log

When you consider how large to make your physical log, you can begin by using the following formula to calculate an approximate size:

PHYSFILE = (connections * max_log_pages_per_crit_sect * 4 * pagesize) 
/ 1024

This PHYSFILE value represents a maximum. For more information on monitoring and tuning the physical log, refer to the chapter on configuration effects on I/O utilization in your IBM Informix: Performance Guide.

Variable in Formula

Description

connections

Maximum number of users that you expect to access the database server concurrently. If you set the NETTYPE parameter, connections is the sum of the values specified in the users field of each NETTYPE parameter in your ONCONFIG file.

max_log_pages_per_crit_sect

Maximum number of pages that the database server can physically log in a critical section.

4

Necessary factor because the following part of the formula represents only 25 percent of the physical log:

connections * max_log_pages_per_crit_sect

pagesize

System page size in bytes that you can obtain with onutil CHECK RESERVED.

1024

Necessary divisor because you specify PHYSFILE parameter in units of kilobytes