Re: cache table vs. indexed table, and multiblock reads

Hi Sweth,

I can't answer the first question for you so I won't try.

As far as the best setting for multiblock reads .... The books don't mention a specific value because it is operating system dependent. You should set it so that

db_file_multiblock_read_count x db_block_size = OS read size

(the number of bytes the OS will read at a time)

regards

Jerry Gitomer

Sweth Chandramouli wrote in message ...
> two quick questions:
>
> 1) when would it make sense to use a cache table versus
>a fully indexed one? as i understand it, the main advantage of
>a cache table is that it disables buffer aging, so that small
>lookup tables that are read via full-table-scans will be read
>into the buffer cache like regular data, instead of being placed
>at the "old" end of the stack, so that it will be overwritten
>immediately. fully indexing a table, on the other hand, prevents
>the full table scan from ever happening, but is mostly useful for
>the same sorts of tables. how should i pick between the two?
>
> 2) i've often been told that, if your os file system
>caching algorithm supports block read-ahead (e.g. solaris), it
>is advantageous to use increase the number of oracle blocks
>that are read at once via the multiblock_read paramater; i've
>never been able to get a good answer as to what value to set
>that paramater to, however. i recently picked up the oracle
>press advanced tuning guide for some more insight into this;
>all that book says, however, is to tune the multiblock reads
>to the optimal value for your operating system. does anyone
>know of any better rules that "set it to the best value", which
>seems to be what the book says? (i'm interested in solaris
>in particular, but would rather understand how to figure out
>the "optimal value" for any os if i understand how that os
>caches file reads.)
>
> tia,
> sweth.
>
>--
>Sweth Chandramouli
>IS Coordinator, The George Washington University
><sweth_at_gwu.edu> / (202) 994 - 8521 (V) / (202) 994 - 0458 (F)
>*
Received on Wed May 05 1999 - 12:56:18 CDT