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Installation and Initial Configuration 1-35
Shared-Memory Parameter Guidelines
CHUNKS
CHUNKS specifies the maximum number of chunks supported by OnLine.
The value specified should be as close as possible to the maximum number
permitted, which is operating-system dependent.
The maximum number of chunks is the lesser of two values:
■ The number of chunk entries (pathnames) that can fit on an OnLine
page
■ The maximum number of open files per process allowed by the
operating system, minus 6
The default value for CHUNKS is 8. For specific instructions on how to
calculate the number of chunk entries that can fit on a page, refer to page 2-93.
DBSPACES
DBSPACES specifies the maximum number of dbspaces supported by
OnLine. The maximum number of dbspaces is equal to the value of CHUNKS,
since each dbspace requires at least one chunk. The minimum value is 1,
representing the root dbspace. The default value is 8.
PHYSBUFF
PHYSBUFF specifies the size in kilobytes of each of the two physical log
buffers in shared memory. Double buffering permits user processes to write
to the active physical log buffer while the other buffer is being flushed to the
physical log on disk.
The recommended value for PHYSBUFF is 16 pages, or 16 multiplied by
BUFFSIZE. (BUFFSIZE is the machine-specific page size and is the last
parameter listed in tbconfig.std.) The default value is 32KB.
LOGBUFF
LOGBUFF specifies the size in kilobytes of each of the three logical log buffers
in shared memory. Triple buffering permits user processes to write to the
active buffer while one of the other buffers is being flushed to disk. If flushing
is not complete by the time the active buffer fills, user processes begin writing
to the third buffer.