sys_attrs_ipc(5)sys_attrs_ipc(5)NAMEsys_attrs_ipc - attributes for the ipc kernel subsystem
DESCRIPTION
This reference page describes attributes for the Interprocess Communi‐
cation (ipc) kernel subsystem.
In the following list, attributes whose names are preceded by an aster‐
isk (*) can be modified at run time as well as at boot time.
See sys_attrs(5) for an introduction to system attributes and how to
set them.
The maximum number of kernel IPC ports that can be used on the
system at one time.
Default value: (task-max * 3 + thread_max) + (thread_max * 2) +
2000
(Values of variables used to establish default value: task_max =
nproc +1; thread_max = nproc *2; nproc = 20 + 8 * maxusers)
Do not modify the default setting for this attribute unless
instructed to do so by support personnel or by patch kit docu‐
mentation.
Maximum size, in bytes, of a single System V message.
Default value: 8192 (bytes, which equal 1 page)
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main
memory on the system. The minimum value (0) disables the messag‐
ing system.
Maximum number of bytes that can be queued to a single System V
message queue.
Default value: 16,384 (bytes, which equal 2 pages)
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main
memory on the system. The minimum value (0) disables the messag‐
ing system.
Maximum number of System V message queues that can be used on
the system at one time.
Default value: 50 (queues) The system rounds the number to the
value associated with the next higher power of two; for example,
64.
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main
memory on the system. The minimum value (0) disables the messag‐
ing system.
Maximum number of messages (system wide) that can be queued to
System V message queues at one time.
Default value: 40 (messages)
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main
memory on the system. The minimum value (0) disables the messag‐
ing system.
The number of buckets in the hash table that the kernel uses to
keep track of PSHARED objects (mutexes, condition variables, and
reader-writer locks). This value must be a power of 2 and is
automatically rounded up to a power of 2 if not entered as such.
Default value: 2048 (buckets)
Minimum value: 512
Maximum value: 1,048,576
Increasing this value might reduce the initialization time of
programs that depend on PSHARED objects.
A value that controls the maximum adjustment that can be made to
any System V semaphore when a process exits.
Default value: 16,384
Minimum value: 0
Maximum value: 65,536
A value that sets the default thread wakeup policy for a System
V semaphore after a change in the semaphore value. When
sem_broadcast_wakeup is 0 (zero), only as many waiting threads
that can make progress are awakened. When sem_broadcast_wakeup
is 1, all threads waiting for the semaphore are awakened.
Default value: 0 (wake up only those threads that can proceed)
The default setting reduces the likelihood that time-critical
applications will encounter delays caused by processes that are
slow to release semaphores. Such delays are more likely to hap‐
pen when an application spawns a large number of threads that
compete for semaphores, and the application is being run on a
system where memory load is high.
Maximum number of System V semaphores that can be used on the
system at one time.
Default value: 10 (semaphores) (The system rounds the number to
the value associated with the next higher power of two; for
example, 16.)
Minimum value: 0
Maximum value: INT_MAX
Maximum number of System V semaphores that can be used by a sin‐
gle process at one time.
Default value: 25 (semaphores)
Minimum value: 0
Maximum value: INT_MAX
Maximum number of operations that can be outstanding on a single
System V semaphore at one time.
Default value: 10 (operations)
Minimum value: 0
Maximum value: INT_MAX
Maximum number of undo operations that can be outstanding on a
single System V semaphore at one time.
Default value: 10 (operations)
Minimum value: 0
Maximum value: INT_MAX
Maximum integer value that any System V semaphore can contain.
Default value: 32,767
Minimum value: 0
Maximum value: INT_MAX, but do not enter values higher than
65535
A value that sets default policy for shared memory allocation on
NUMA-enabled systems (GS80, GS160, GS320). A value of 1 means
that shared memory is striped across Resource Affinity Domains
(RADs). A value of 0 means that shared memory is not striped
across RADs.
Default value: 1
Although you can change the value of this attribute while the
system is running, there are currently no known situations for
which the shm_allocate_striped value should be changed. A value
of 1 is the recommended default policy for all applications on
NUMA-enabled systems. Furthermore, changing the value to 0 on
these systems does not override use of striped memory allocation
by applications that explicitly specify and control it through
NUMA-specific programming interfaces.
This attribute has no effect on platforms that do not use NUMA
architecture.
See numa_intro(3) for an introduction to NUMA.
Disables (0) or enables (1) the dumping of shared memory regions
to the core file. The attribute is only used in conjunction
with shared memory.
Default value: 1 (on).
Maximum size, in bytes, of a single System V shared memory
region.
Default value: 4,194,304 (bytes) (This value equals 512 pages)
Minimum size, in bytes, of a single System V shared memory
region.
Default value: 1 (All requests are rounded to the next page
size.)
Maximum number of shared memory regions that can be used on the
system at one time.
Default value: 100 (regions) (The system rounds the number to
the value associated with the next higher power of two; for
example, 128.)
Maximum number of System V shared memory regions that can be
attached to a single process at one time.
Default value: 32 (regions)
If enabled (1), writes segmented shared memory contents when an
application issues a core dump. If disabled (0), segmented
shared memory is not written to the core dump.
Default value: 1 (enabled)
Because segmented shared memory can be large, the amount of
time needed to dump the region to a core file and the amount of
file system space required by the operation can be extensive,
especially in large database environments. Therefore, although
shared memory can be useful for debugging, you may not want to
include it in core files because of time and resource limita‐
tions.
This attribute can be modified at run time.
The minimum size, in bytes, of a System V shared region for the
use of shared page tables. Setting this value to 0 disables
the use of shared page tables for shared memory. The size must
be at least equal to the value of SSM_SIZE, which is defined in
the machine/pmap.h file (the default is 8 MB).
This attribute can be modified at run time.
Default value: SSM_SIZE
Minimum value: SSM_SIZE
SEE ALSOsys_attrs(5)
System Configuration and Tuning
sys_attrs_ipc(5)
