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Don Burleson Blog 









Oracle 8i hidden database parameters

Don Burleson


Note: Oracle hidden parameters are undocumented and unsupported by Oracle.
Make sure that you thoroughly test all hidden parameters before placing them in your production environment.

Parameter Name                            Description
----------------------------------------- --------------------------------------------------------------
_db_aging_cool_count                      Touch count set when buffer cooled
_db_aging_freeze_cr                       Make CR buffers always be too cold to keep in cache
_db_aging_hot_criteria                    Touch count which sends a buffer to head of replacement list
_db_aging_stay_count                      Touch count set when buffer moved to head of replacement list
_db_aging_touch_time                      Touch count which sends a buffer to head of replacement list
_db_always_check_system_ts                Always perform block check and checksum for System tablespace
_db_block_buffers                         Number of database blocks cached in memory: hidden parameter
_db_block_cache_clone                     Always clone data blocks on get (for debugging)
_db_block_cache_num_umap                  number of unmapped buffers (for tracking swap calls on blocks)
_db_block_cache_protect                   protect database blocks (true only when debugging)
_db_block_check_for_debug                 Check more and dump block before image for debugging
_db_block_granule_interval                number of granules to process
_db_block_hash_buckets                    Number of database block hash buckets
_db_block_hash_latches                    Number of database block hash latches
_db_block_hi_priority_batch_size          Fraction of writes for high priority reasons
_db_block_lru_latches                     number of lru latches
_db_block_max_cr_dba                      Maximum Allowed Number of CR buffers per dba
_db_block_max_dirty_target                Upper bound on modified buffers/recovery reads
_db_block_max_scan_pct                    Percentage of buffers to inspect when looking for free
_db_block_med_priority_batch_size         Fraction of writes for medium priority reasons
_db_block_numa                            Number of NUMA nodes
_db_block_prefetch_quota                  Prefetch quota as a percent of cache size
_db_block_trace_protect                   trace buffer protect calls
_db_cache_advice_batch_size               cache advisory simulation batch size
_db_cache_advice_sample_factor            cache advisory sampling factor
_db_file_direct_io_count                  Sequential I/O buf size
_db_file_noncontig_mblock_read_count      number of noncontiguous db blocks to be prefetched
_db_handles                               System-wide simultaneous buffer operations
_db_handles_cached                        Buffer handles cached each process
_db_large_dirty_queue                     Number of buffers which force dirty queue to be written
_db_mttr_advice                           MTTR advisory
_db_mttr_partitions                       number of partitions for MTTR advisory
_db_mttr_sample_factor                    MTTR simulation sampling factor
_db_mttr_sim_target                       MTTR simulation targets
_db_mttr_sim_trace_size                   MTTR simulation trace size
_db_mttr_trace_to_alert                   dump trace entries to alert file
_db_percent_hot_default                   Percent of default buffer pool considered hot
_db_percent_hot_keep                      Percent of keep buffer pool considered hot
_db_percent_hot_recycle                   Percent of recycle buffer pool considered hot
_db_writer_chunk_writes                   Number of writes DBWR should wait for
_db_writer_histogram_statistics           maintain dbwr histogram statistics in x$kcbbhs
_db_writer_max_writes                     Max number of outstanding DB Writer IOs
_db_writer_scan_depth_pct                 Percentage of LRU buffers for dbwr to scan when looking for dirt



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