IBM 000-8697 User Manual
9-10
IBM Informix OnLine Database Server Administrator’s Guide
How Multiple Residency Works
How Multiple Residency Works
Multiple residency is possible because separate shared-memory segments
can be maintained for each instance of OnLine. The link between each
OnLine instance and its associated shared-memory segments is the value of
can be maintained for each instance of OnLine. The link between each
OnLine instance and its associated shared-memory segments is the value of
SERVERNUM
.
Under the
UNIX
operating system, each OnLine user process that wishes to
attach to shared memory passes to the operating system a shared-memory
key value. The key value is used to specify the shared-memory area that the
process might attach to.
key value. The key value is used to specify the shared-memory area that the
process might attach to.
OnLine incorporates the value of the configuration parameter
SERVERNUM
into the calculation to arrive at the shared-memory key. Thus, before a user
process can attach to shared memory, it reads the value of the
process can attach to shared memory, it reads the value of the
SERVERNUM
from the configuration file specified by the environment variable
TBCONFIG
,
and uses the value to calculate the shared-memory key. You maintain
separation between the OnLine systems by maintaining multiple configu-
ration files, each with a unique
separation between the OnLine systems by maintaining multiple configu-
ration files, each with a unique
SERVERNUM
value. (Refer to
more details about how a user process attaches to shared memory. Refer to
for more details about the way in which
TBCONFIG
specifies the
OnLine configuration file for each user. )
It becomes your responsibility as administrator to ensure that each instance
of OnLine is associated with a unique
of OnLine is associated with a unique
SERVERNUM
value, and that each user
with access to OnLine correctly sets his or her
TBCONFIG
environment
variable. You also must keep all disk space allocations separate by ensuring
that chunk pathnames are not duplicated among the separate OnLine
instances. In this way, multiple OnLine database servers execute concur-
rently and completely independently in different areas of shared memory
and disk space.
that chunk pathnames are not duplicated among the separate OnLine
instances. In this way, multiple OnLine database servers execute concur-
rently and completely independently in different areas of shared memory
and disk space.
There is no change to OnLine administration under multiple residency.
However, recognize that you have to maintain logical logs for each OnLine
instance. If you can dedicate a tape drive to each OnLine database server, you
can use the continuous logging option. Otherwise, you must plan your
logical log backup schedules and archive schedules carefully.
However, recognize that you have to maintain logical logs for each OnLine
instance. If you can dedicate a tape drive to each OnLine database server, you
can use the continuous logging option. Otherwise, you must plan your
logical log backup schedules and archive schedules carefully.