Installation and Initial Configuration 1-33
Shared-Memory Parameter Guidelines
USERS
USERS specifies the maximum number of user processes that can concur-
rentlyattach to shared memory. The value can have a large effect on the size
ofshared memory because it determines the minimum values for four other
shared-memory parameters (LOCKS,TBLSPACES,BUFFERS, and
TRANSACTIONS.)
Toarrive at a value for USERS, specify the highest likely value for the number
ofuser processes active at any one time plus the value of CLEANERS, plus 4.
Add one more user process if you intend to implement mirroring.
The minimum value is equal to the value ofCLEANERS plus 4, plus 1 if
mirroring is enabled. The maximum value is 1000. The default value is 20.
(The four required user processes are the master daemon,tbinit; the under-
taker daemon,tbundo; the DB-M onitor process,tbmonitor; and one
additionaluser process to ensure a slot for an administrative process. If you
enable mirroring, an additional mirror daemon is needed.)
TRANSACTIONS
The value ofTRANSACTIONS refers to the maximum number of concurrent
transactions supported by OnLine.
The minimum value ofTRANSACTIONS is the value of USERS. The
maximum value is the number of transactions that can fit into a checkpoint
record, which for OnLine 5.x is 1,364.
By default, OnLine sets the value of TRANSACTIONS equal to the value of
USERS.DB-Monitordoes not prompt for this value during initialization. The
default value is appropriate unless you plan to use OnLine in anX/Open
environment. If you are configuring OnLine for use withIBM Informix
TP/XA, refer to theIBM Informix TP/XA User Manual.
LOCKS
LOCKSspecifies the maximum number of locks available to OnLine user
processesduring processing. The number of locks has a relatively small effect
on the size of shared memory. The minimum value forLOCKS is equal to 20
locksper user process. The maximum value is 8 million. The default value is
2000.