AIX Version 4.3 Differences Guide

2.12.3 Larger Pipe Buffer Pool
The increased size of the kernel heap means that more space can be used for
pipe buffers by the kernel, therefore increasing the number of simultaneously
open pipes. As with the mbuf pool, the amount of kernel virtual memory reserved
for the pipe buffer pool depends on the total amount of physical memory. The
system will allocate an amount of virtual memory equivalent to one eighth of the
physical memory, or 64 MB, whichever is smaller, with a minimum allocation of 16
MB. Of the memory reserved for use as pipe buffers, 1 MB is pinned in physical
memory for faster initial buffer allocation. The size of each individual pipe buffer
remains the same as on previous versions of AIX, at 4 KB.
2.12.4 Inter-Process Communication Identifier Enhancement
The limits of the maximum number of IPC identifiers have been increased, as
provided in Table 6.
Table 6. IPC Identifier Limits
Value Previous Limit New Limit
Message queue IDs 4096 131072
Semaphore set IDs 4096 131072
Shared memory IDs 4096 131072
In addition to increasing the number of identifiers available, AIX Version 4.3.2 has
also implemented a new algorithm to handle the ipcget() routine.
The previous implementation used a sequential search algorithm for traversing
the list of IPC identifiers. For a table size of N, the algorithm resulted in N
operations for a search miss and N/2 operations for a search hit. Although this is
very simple, it does not scale very well. The algorithm has been replaced with a
hash table implementation that is better matched to the larger number of IPC
identifiers now available.
The IPC support commands, such as ipcrm and ipcs, have also been changed to
take account of the increased limits.
2.12.5 Boot Logical Volume Scaling
In AIX 4.3.2, the boot logical volume is expanded to enable system configurations
with up to 1,000 devices.
As more and more devices are added to a system, the ODM object classes
containing device configuration data will grow larger and larger. It is possible that
the RAM file system used in the initial stages of booting will not be large enough
for the larger ODM files. The existing boot process accounts for this when booting
from disk by dynamically expanding the RAM file system based on the amount of
system memory. The increased savebase area will not fit on the boot logical
volume when adding large amount of devices.
2.13 Scheduler Enhancements (4.3.2)
The scheduler on AIX Version 4.3.2 has been enhanced to increase the impact of
using the nice command to alter the priority of a thread. The following sections
24 AIX Version 4.3 Differences Guide