1-26 IBM Informix OnLine Database Server Administrator’s Guide
Logical Log Configuration Guidelines
Refer to page 1-42 for guidelines on deciding how much disk space should be
dedicated to OnLine dbspaces. Refer to page 1-26 for information about
sizing the logical log files.
The default value of PHYSDBS is 1,000 KB.
The default values included in the tbconfig.std file adhere to both of the
guidelines just described. The size of the physical log is 1,000 KB. The default
value of
LOGSIZE is 500 KB. The default value of LOGFILES is 6. Thus, total
logical log size is 3,000 KB. Total space devoted to the physical and logical
logs is 4,000 KB. This value meets the first criterion of 20 percent of the root
dbspace, which is 20,000 KB. The strategy also meets the second recommen-
dation to allocate logging space in a ratio of 3:1, logical log space to physical
log space.
Logical Log Configuration Guidelines
This section describes how to assign initial configuration values to the logical log
parameters. Refer to page 3-14 for a detailed discussion of logical log configu-
ration guidelines. Refer topage 4-18 for an overviewof the mechanics ofOnLine
blobspace and dbspace logging.
OnLine supports transaction logging, which is the ability of the database
server to track and, if needed, to roll back all changes made to the database
during application transactions. OnLine transaction logging is implemented
by recording each change made to a database in disk space allocated for the
OnLine logical log files.
The logical log files contain a history of all database changes since the time of
the last archive. At any time, the combination of OnLine archive tapes plus
OnLine logical log files contain a complete copy of your OnLine data.
As OnLine administrator, you decide on the optimum total size of the logical
log: LOGFILES multiplied by LOGSIZE. The optimum size of the logical logs is
based on the length of individual transactions. (OnLine does not permit a
single transaction to span all logical log files.) Refer to page 2-156 for detailed
information on selecting values for LOGFILES and LOGSIZE that are specifi-
cally tuned to your application environment.
