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沒有必要使用了onments.
本身extended storage的用途就是在32位內存模型的共享內存限制上增加可以使用的內存，但是要減少agent的256MB的共享內存尋址空間。因為64位的可以說沒有共享內存的限制，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.
這里為什么說共享內存段最多只有16個256M（總和是4G能理解，但是單個segment大小為什么最大是256M呢？）是操作系統的規定嗎？？
還有為什么說DB2最多能使用7個？也是操作系統的限制嗎？