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