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Don Burleson Blog 







 _index_prefetch_factor Tips

Oracle Database Tips by Donald BurlesonMarch 11, 2015

Question:  How do I use the _index_prefetch_factor hidden parameter.  Will _index_prefetch_factor Tips  increase the number of multi-block reads on index range scans?

Answer:  The _index_prefetch_factor is an undocumented parameter that defaults to a value of 100.  When setting _index_prefetch_factor to a value smaller than 100, it increases the propensity that Oracle will invoke multi-block reads on an index range scan or index full scan.  The v$sysstat and v$sesstat and AWR report also provide information on prefetch operations.  Prefetch operations in an AWR report include:

- index crx upgrade (prefetch)                   
- physical reads cache prefetch            
- physical reads prefetch warmup
- prefetch warmup blocks aged out
- prefetched blocks aged out before

Also, the 10299 trace event measures prefetch operations.

Also see my related notes on db_file_noncontig_mblock_read_count.

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