Performance of query , What if db_recycle_cache_size is zero

Question

Hi
in our 11g Database , We have some objects for which default buffer pool is recycle pool.But i observed recycle pool size is zero (db_recycle_cache_size = 0 ).
Now if we issue a sql for which we need to access these objects , what happen ? i strongly think as there is no recycle bin , it will go in to traditional default buffer cache and obey normal LRU algorithm.Am i missing something here ?
The issue we face is , we have a query which is picking up correct index but it takes around 3 Minutes.I see that the step which takes more time is index range sacn which fetches around 50k records and takes 95% of whole query execution time.Then i observed that index is configured to have default pool as recycle pool.If i rerun the same query again and again , execution times are close to zero (No wonder , no physical reads in subsequent execution).
I am thinking of setting up recycel pool .What else i may need to consider tuning this query ?
Thanks and Regards
Pram

Answer 1

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Now if we issue a sql for which we need to access these objects , what happen ? i strongly think as there is no recycle bin , it will go in to traditional default buffer cache and obey normal LRU algorithm.Am i missing something here ?
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Recycle bin? What does that have to do with anything?
You are correct - with no keep or recycle cache the default buffer cache and LRU are used for aging.
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I am thinking of setting up recycel pool .
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Why - it doesn't sound like you know the purpose of the recycle pool. See '7.2.4 Considering Multiple Buffer Pools' in the Performance Tuning Guide
http://docs.oracle.com/cd/B28359_01/server.111/b28274/memory.htm
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With segments that have atypical access patterns, store blocks from those segments in two different buffer pools: the KEEP pool and the RECYCLE pool. A segment's access pattern may be atypical if it is constantly accessed (that is, hot) or infrequently accessed (for example, a large segment accessed by a batch job only once a day).
Multiple buffer pools let you address these differences. You can use a KEEP buffer pool to maintain frequently accessed segments in the buffer cache, and a RECYCLE buffer pool to prevent objects from consuming unnecessary space in the cache. When an object is associated with a cache, all blocks from that object are placed in that cache. Oracle maintains a DEFAULT buffer pool for objects that have not been assigned to a specific buffer pool. The default buffer pool is of size DB_CACHE_SIZE. Each buffer pool uses the same LRU replacement policy (for example, if the KEEP pool is not large enough to store all of the segments allocated to it, then the oldest blocks age out of the cache).
By allocating objects to appropriate buffer pools, you can:
•Reduce or eliminate I/Os
•Isolate or limit an object to a separate cache
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Using a recycle pool isn't going to affect that initial 3 minute time. It would keep things from being aged out of the default cache when the index blocks are loaded.
Further using a recycle pool could cause those 'close to zero' times for the second and third access to increase if the index blocks from the first query were 'recycled' so another query could use the blocks. Recycle means - thow-it-away when you are done if you want.
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What else i may need to consider tuning this query ?
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If it ain't broke, dont' fix it. You haven't shown that there is anything wrong with the query you are talking about. How could we possibly know if 3 minutes if really slow or if it is really fast? You haven't posted the query, an execution plan, row counts for the tables or counts for the filter predicates.
See this AskTom article for his take on the RECYCLE and other pools.