9i and DB_BLOCK_LRU_LATCHES

[Orca777]

Hi,

9i DB_BLOCK_LRU_LATCHES ist no longer supported, how does oracle control the number of lru_latches and how can is see/select it?

Orca

[chao_ping]

hi, It is undocumented now.

21:04:30 SQL> @undocu

NAME VALUE D S S M A DESCRIPTION
------------------------------ ------------------------------ - - - - - ----------------------------------------------------------------
_db_block_buffers 152022 Y N N N N Number of database blocks cached in memory: hidden parameter
_db_block_cache_clone FALSE Y N N N N Always clone data blocks on get (for debugging)
_db_block_cache_num_umap 0 Y N N N N number of unmapped buffers (for tracking swap calls on blocks)
_db_block_cache_protect FALSE Y N N N N protect database blocks (true only when debugging)
_db_block_check_for_debug FALSE Y N I N N Check more and dump block before image for debugging
_db_block_granule_interval 10 Y N I N N number of granules to process
_db_block_hash_buckets 304049 Y N N N N Number of database block hash buckets
_db_block_hash_latches 2048 Y N N N N Number of database block hash latches
_db_block_hi_priority_batch_si 0 Y N N N N Fraction of writes for high priority reasons
ze


NAME VALUE D S S M A DESCRIPTION
------------------------------ ------------------------------ - - - - - ----------------------------------------------------------------
_db_block_lru_latches 32 Y N N N N number of lru latches
_db_block_max_cr_dba 6 Y N N N N Maximum Allowed Number of CR buffers per dba
_db_block_max_dirty_target 0 Y N I N N Upper bound on modified buffers/recovery reads
_db_block_max_scan_pct 40 Y N N N N Percentage of buffers to inspect when looking for free
_db_block_med_priority_batch_s 0 Y N N N N Fraction of writes for medium priority reasons
ize

_db_block_numa 1 Y N N N N Number of NUMA nodes
_db_block_prefetch_quota 10 Y N I N N Prefetch quota as a percent of cache size
_db_block_trace_protect FALSE Y N I N N trace buffer protect calls

[Orca777]

Good,
can you post me your script?
Thank you very much
Orca

[ggnanaraj]

Originally posted by Orca777
9i DB_BLOCK_LRU_LATCHES ... how can is see/select it?

select count(*) from v$latch_children
where name = 'cache buffers lru chain';

From metalink...
In Oracle9i, the parameter DB_BLOCK_LRU_LATCHES is obsolete (listed in the desupported/depreciated init.ora parameter section of the Oracle 9i New Features guide). This is now a hidden parameter that defaults based on the value of cpu_count or db_writer_processes if explictly set, as well as several other factors(which includes the max # of caches ). A setting of db_writer_processes = 4 seems to adjust the hidden parameter to 32. Since this is now a hidden parameter, I would keep in mind that the formula (and therefore the value)is subject to change with subsequent versions.

HTH.

[Orca777]

Thanks a lot!!
Orca


PS.: what is the select for internal paramts ( some k$-Table ??)

[ggnanaraj]

Yet another note from metalink...

You cannot set DB_BLOCK_LRU_LATCHES in 9i--it is computed automatically. The number of LRU latches in each buffer pool for each block size will be equal to the half the number of CPUs.

HTH.

[adewri]

Script for finding undocumented parameters

SELECT   a.ksppinm parameter
        ,a.ksppdesc description
        ,b.ksppstvl session_value
        ,c.ksppstvl instance_value
    FROM x$ksppi a
        ,x$ksppcv b
        ,x$ksppsv c
   WHERE a.indx = b.indx AND a.indx = c.indx AND SUBSTR (a.ksppinm
                                                        ,1
                                                        ,1
                                                        ) = '_'
ORDER BY a.ksppinm
/

HTH

[ggnanaraj]

http://download-west.oracle.com/docs...ges.htm#647062

[pando]

just use v$fixed_view_definition

[Orca777]

This is extraordinary!!
I post a topic and
you answered it all perfectly in < 5 Minutes!!

:-)))))))))))))))))

Orca