Database Reference
In-Depth Information
Column (#4): LOCATION_ID(NUMBER)
AvgLen: 3.00 NDV: 7 Nulls: 0 Density: 0.018519 Min: 1400 Max: 2700
Histogram: Freq #Bkts: 7 UncompBkts: 27 EndPtVals: 7
Index Stats::
Index: DEPT_ID_PK Col#: 1
LVLS: 0 #LB: 1 #DK: 27 LB/K: 1.00 DB/K: 1.00 CLUF: 1.00
Index: DEPT_LOCATION_IX Col#: 4
LVLS: 0 #LB: 1 #DK: 7 LB/K: 1.00 DB/K: 1.00 CLUF: 1.00
…
Table 7-2.
Abbreviations Used in the Section “Base Statistical Information”
Abbreviation
Meaning
Dictionary View (and Column)
DBA_TAB_HISTOGRAMS
#Bkts
Number of histogram buckets
DBA_TABLES.BLOCKS
#Blks
Number of table blocks below the
high water mark
DBA_INDEXES.DISTINCT_KEYS
#DK
Distinct keys
DBA_INDEXES.LEAF_BLOCKS
#LB
Number of index leaf blocks
DBA_TABLES.NUM_ROWS
#Rows
Number of table rows
DBA_TAB_COLUMNS.AVG_COL_LEN
AvgLen
Average column value length
DBA_TABLES.AVG_ROW_LEN
AvgRowLen
Average row length
DBA_TAB_HISTOGRAMS
EndPtVals
Histogram end point values
DBA_INDEXES.CLUSTERING_FACTOR
CLUF
Clustering factor
DBA_INDEXES.AVG_DATA_BLOCKS_PER_K
EY
DB/K
Average number of index data blocks
per key
DBA_INDEXES.AVG_LEAF_BLOCKS_PER_K
EY
LB/K
Average number of index leaf blocks
per key
DBA_INDEXES.BLEVEL
LVLS
B-tree level
DBA_TAB_COLUMNS.NUM_DISTINCT
NDV
Number of distinct values
UncompBkts
Uncompressed buckets
n/a
The clustering factor is an indication of how clustered (beneficial) or randomly distributed
(detrimental) data is in a table's segment. Indexes are always sorted. When individual index
blocks point to many table blocks, data pertaining to a range of index keys is randomly distributed
within a table's segment, and a high clustering factor, which renders index access unattractive,
results.
When histograms are absent, the following holds for density:
1
NDV
Density
=
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