Posted on 2010-03-23 16:08
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DB2
EXTENDED STORAGE/NOT EXTENDED STORAGE
EXTENDED STORAGE/NOT EXTENDED STORAGE: Specifies whether buffer pool victim pages will be copied to a secondary cache called extended storage. Extended storage is more efficient than retrieving data from disk but less efficient than retrieving data from the buffer pool, so it is not applicable to 64-bit envir没有必要使用了onments.
本身extended storage的用途就是在32位内存模型的共享内存限制上增加可以使用的内存，但是要减少agent的256MB的共享内存寻址空间。因为64位的可以说没有共享内存的限制，自然
In 32-bit AIX, there are a maximum of 16, 256 MB memory segments addressable by a process. Of these, only seven can be used by DB2 for shared memory. Of these seven segments (or 1.75 GB), one is used for memory mapped I/O, and one may be used by the fast communications manager (FCM) for inter- or intra-partition communication (if there are multiple database partitions or intra-partition parallelism is enabled). To maximize the amount of shared memory that can be used for the buffer pool, memory-mapped I/O can be disabled, and the FCM can be forced to use the network instead of shared memory.
这里为什么说共享内存段最多只有16个256M（总和是4G能理解，但是单个segment大小为什么最大是256M呢？）是操作系统的规定吗？？
还有为什么说DB2最多能使用7个？也是操作系统的限制吗？