Re: The Cache option

In article <9a7hn8$1ufg$1_at_newssvr05-en0.news.prodigy.com>, Beldar <beldar_from_remulac_at_yahoo.com> writes:
>The Cache option of the Create Table and Alter Table commands ensures that
>the first time a table is accessed, the entire table is loaded into the SGA
>and marked as 'most recently used'. According to Oracle doc, this data is
>still subject to LRU algorithms, yet stays in the SGA longer than normal.
>HOW? Isn't every block marked 'most recently used' when it's first
>accessed?
>
>

Prior to version 8.1 when Oracle read blocks into the shared pool all index blocks and table blocks read via a random read were place on the most recently used end of the LRU chain, but table blocks read by full table scan were placed on the not recently used end of the chain. Oracle assumed that table blocks read by full table scan were not going to be needed again so they could be almost instantly overlaid by other read requests. The cache parameter causes blocks read by a table scan to be treated like index and table bocks read by randon reads.

One of the upgrade documents for version 8.1 states that Oracle has made a change to the way it handles the buffer pool LRU but I am not sure of the details.

• Mark D. Powell --
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