I would not use the keep pool, the default buffer cache is almost certainly better than good enough.
The keep buffer would definitely be in the SGA, it is just another buffer cache.When we assign any segment to KEEP buffer pool, data will be always available
in buffer cache so that we can avoid physical reads
that is absolutely NOT correct. The keep pool is just a buffer cache. There is no "data will always be available" about it, it is just like the default pool (it caches blocks)
<quote src = Expert Oracle Database Architecture>Block Buffer Cache
So far, we have looked at relatively small components of the SGA. Now we are going to look at one that is possibly huge in size. The block buffer cache is where Oracle stores database blocks before writing them to disk and after reading them in from disk. This is a crucial area of the SGA for us. Make it too small and our queries will take forever to run. Make it too big and we¿ll starve other processes (e.g., we won¿t leave enough room for a dedicated server to create its PGA, and we won¿t even get started).
In earlier releases of Oracle, there was a single block buffer cache, and all blocks from any segment went into this single area. Starting with Oracle 8.0, we had three places to store cached blocks from individual segments in the SGA:
* Default pool: The location where all segment blocks are normally cached. This is the original¿and previously only¿buffer pool.
* Keep pool: An alternate buffer pool where by convention you would assign segments that were accessed fairly frequently, but still got aged out of the default buffer pool due to other segments needing space.
* Recycle pool: An alternate buffer pool where by convention you would assign large segments that you access very randomly, and which would therefore cause excessive buffer flushing but would offer no benefit because by the time you wanted the block again it would have been aged out of the cache. You would separate these segments out from the segments in the default and keep pools so that they would not cause those blocks to age out of the cache.
Note that in the keep and recycle pool descriptions I used the phrase 'by convention.' There is nothing in place to ensure that you use neither the keep pool nor the recycle pool in the fashion described. In fact, the three pools manage blocks in a mostly identical fashion; they do not have radically different algorithms for aging or caching blocks.
The goal here was to give the DBA the ability to segregate segments to hot, warm, and do not care to cache areas. The theory was that objects in the default pool would be hot enough (i.e., used enough) to warrant staying in the cache all by themselves. The cache would keep them in memory since they were very popular blocks. You might have had some segments that were fairly popular, but not really hot; these would be considered the warm blocks. These segments' blocks could get flushed from the cache to make room for some blocks you used infrequently (the 'do not care to cache' blocks). To keep these warm segments blocks cached, you could do one of the following:
* Assign these segments to the keep pool, in an attempt to let the warm blocks stay in the buffer cache longer.
* Assign the 'do not care to cache' segments to the recycle pool, keeping the recycle pool fairly small so as to let the blocks come into the cache and leave the cache rapidly (decrease the overhead of managing them all).
This increased the management work the DBA had to perform, as there were three caches to think about, size, and assign objects to. Remember also that there is no sharing between them, so if the keep pool has lots of unused space, it won¿t give it to the overworked default or recycle pool. All in all, these pools were generally regarded a very fine, low-level tuning device, only to be used after most all other tuning alternatives had been looked at (if I could rewrite a query to do one-tenth the I/O rather then set up multiple buffer pools, that would be my choice!).
Read also http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:253415112676
Based on your misunderstanding of what the keep pool is/does, I would really recommend you do not use it. It does not do what you imagine.
If your tables are less than about 2% the size of the buffer cache - they will be cached normally in the default pool. If they exceed 2% of the buffer cache, they will not be cached "normally" (read the above link) in order to avoid blowing out the buffer cache.