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Oracle Tips by Burleson |
Data Buffer Pool Parameters
This class of hidden parameters controls the
internal workings of the RAM data buffers. The most
frequently-used parameters for the data buffers include:
* _db_percent_hot_keep – This is the percent
of KEEP buffer pool that should be considered hot
* _db_aging_hot_criteria – This is based in
the x$bh.tch (touch count) which sends a buffer to head of replacement
list
Data Buffer Pool
List of undocumented Oracle parameters
Parameter
Current Instance
Name
Value Value
---------------------------------------- ----------
--------------------
Parameter Description
-------------------------------------------------------------------------------_PX_use_large_pool
FALSE FALSE
Use Large Pool as source of PX buffers
_close_cached_open_cursors
FALSE FALSE
close cursors cached by PL/SQL at each commit
_db_aging_hot_criteria
2 2
Touch count which sends a buffer to head of replacement list
_db_handles_cached
5 5
Buffer handles cached each process
_db_percent_hot_default
50 50
Percent of default buffer pool considered hot
_db_percent_hot_keep
0 0
Percent of keep buffer pool considered hot
_db_percent_hot_recycle
0 0
Percent of recycle buffer pool considered hot
_dbwr_async_io
TRUE TRUE
Enable dbwriter asynchronous writes
_dss_cache_flush
FALSE FALSE
enable full cache flush for parallel execution
_filesystemio_options
asynch asynch
IO operations on filesystem files
_io_slaves_disabled
FALSE FALSE
Do not use I/O slaves
_ldr_io_size
262144 262144
size of write IOs used during a load operation
_lm_cache_res_cleanup
25 25
percentage of cached resources should be cleanup
_number_cached_attributes
10 10
maximum number of cached attributes per instance
_parallel_min_message_pool
64440 64440
minimum size of shared pool memory to reserve for pq servers
_row_cache_buffer_size
200 200
size of row cache circular buffer
_row_cache_cursors
10
10
number of cached cursors for row cache management
_row_cache_instance_locks
100 100
number of row cache instance locks
_shared_pool_reserved_min_alloc
4400 4400
minimum allocation size in bytes for reserved area of shared poo
_shared_pool_reserved_pct
5 5
percentage memory of the shared pool allocated for the reserved
_smm_auto_max_io_size
252 252
Maximum IO size (in KB) used by sort/hash-join in auto mode
_smm_auto_min_io_size
60 60
Minimum IO size (in KB) used by sort/hash-join in auto mode
For more details, see the "Easy
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experts to get you started fast with Oracle database technology.
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