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dc_histogram_data statistic meaning

Posted on 2003-03-11
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Hi,
  I have gor some values form v$rowcache, I was wondering what are they
about.
  I mean I got

  Parameter Gets GetMisses Count Hit Ratio
  dc_histogram_data 10763 3153 14 70
  dc_histogram_data_values 7661 1911 12 75

  And the hit is to raise them.First of all I'd like to know what these
  perameters refer to and then how could I raise the Hit?? What should I do?
  What is the meaning of dc_histogram_data and dc_histogram_data_values??
Are
  the statistic collection either made too often or to rarely?



Best Regards
Mario
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Question by:mariorossi663
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DrJekyll earned 1000 total points
ID: 8111548
V$ROWCACHE refers to the dictionary cache. There is not
much tuning that can be done here except by increasing
SHARED_POOL_SIZE.
The dynamic performance table containing measures of all data dictionary activity since the most recent instance startup. Values for each variable of the oraDbRowCacheTable of the private Oracle Database MIB are retrieved directly from a corresponding variable in V$ROWCACHE
 
COUNT Total number of entries in the cache
 
GETS Total number of requests for information on the data object
 
GETMISSES
 Number of data requests resulting in cache misses
 
HitRatio - Percentage data was found in the cache.

You should try to achieve a rate of 90-95% hit ratio.
You can increase the SHARED_POOL_SIZE parameter in
init<sid>.ora file.
You have to monitor this overtime. For example if
you just start your instance you will have a low
hit ratio as nothing is in the cache yet.  Check during
normal working times and at peak times.

Summary: INCREASE SHARED_POOL_SIZE
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Expert Comment

by:Mark Geerlings
ID: 8114547
Just for comparison, I ran the following query in our production data base (about 250 users and usually good response times) and got the following results:

select parameter, gets "Gets", getmisses "Misses",
round((gets * 100) / greatest((gets + getmisses),1),1) "Hit Ratio"
from v$rowcache;

PARAMETER                              Gets     Misses Hit Ratio
-------------------------------- ---------- ---------- ---------
dc_free_extents                         139         93      59.9
dc_used_extents                         139        139      50.0
dc_segments                           69330       3806      94.8
dc_tablespaces                       256509         44     100.0
dc_tablespace_quotas                  24884         65      99.7
dc_files                               2711         35      98.7
dc_users                             422294       1302      99.7
dc_rollback_segments                  11782         37      99.7
dc_objects                            75209      18051      80.6
dc_global_oids                           69         17      80.2
dc_constraints                          148         84      63.8
dc_object_ids                         37067       8406      81.5
dc_synonyms                           13202        124      99.1
dc_sequences                            945         85      91.7
dc_usernames                          82322       1310      98.4
dc_database_links                       255         10      96.2
dc_histogram_defs                    325735      17271      95.0
dc_outlines                               0          0        .0
dc_profiles                            2142          3      99.9
ifs_acl_cache_entries                     0          0        .0
dc_users                                292          8      97.3
dc_sequence_grants                      150         49      75.4
dc_histogram_data                         0          0        .0
dc_histogram_data_values                  0          0        .0
dc_user_grants                       349345        195      99.9

25 rows selected.

Note: We do not have any histograms in our database, so I'm not surprised at the zeroes for those in our system.
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by:anand_2000v
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