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System Architecture 2-49
Shared-Memory Internal Tables
■ User processes waiting for the buffer
Each buffer header maintains a list of the user processes that are
waiting for the buffer and the lock-access level that each waiting
process requires.
Each OnLine buffer is represented as one entry in the buffer header table.
Each entry in the buffer header table occupies 54 bytes.
The number of entries in the buffer header hash table is based on the number
of allocated buffers. The maximum number of hash values is the largest
power of 2 that is less than the value of BUFFERS.
Each entry in the buffer hash table occupies 16 bytes.
The minimum number of OnLine buffers is based on the number of OnLine
user processes (specified as USERS in the configuration file). You must
allocate at least four buffers per user process. The maximum number of
allocated buffers is 32,000.
OnLine Chunk Table
The chunk table tracks all chunks in the OnLine system. If mirroring has been
enabled, an identical mirror chunk table is created when shared memory is
initialized. The mirror chunk table tracks all mirror chunks. If mirroring is
not enabled, the mirror chunk table is not created.
The chunk table in shared memory contains information that enables OnLine
to locate chunks on disk. This information includes the chunk number and
the next chunk in the dbspace. Flags also describe chunk status: mirror or
primary; offline, online, or recovery mode; and whether this chunk is part of
a blobspace.
The maximum number of entries in the chunk table is equal to the value of
CHUNKS, as specified in the configuration file.
Refer to page 3-70 for information about monitoring the chunks using
tbstat -d and tbstat -D.
The maximum number of chunks that can exist within an OnLine configu-
ration might be operating-system dependent. The maximum value is the
lesser of two values: