index_stats视图各列的含义

index_stats视图来收集B树索引的统计信息。可以从中查到该用户拥有索引的名字，高度等等详细信息，以下是其具体的列名及其含义。

INDEX_STATS

statistics on the b-tree

Columns 

   ___________________________ 

   OPT_CMPR_PCTSAVE 

      percentage storage saving expected from optimal prefix compression 

   HEIGHT 

      height of the b-tree 

   BLOCKS 

      blocks allocated to the segment 

   NAME 

      name of the index 

   PARTITION_NAME 

      name of the index partition,if partitioned 

   LF_ROWS 

      number of leaf rows (values in the index) 

   LF_BLKS 

      number of leaf blocks in the b-tree 

   LF_ROWS_LEN 

      sum of the lengths of all the leaf rows 

   LF_BLK_LEN 

      useable space in a leaf block 

   BR_ROWS 

      number of branch rows 

   BR_BLKS 

      number of branch blocks in the b-tree 

   BR_ROWS_LEN 

      sum of the lengths of all the branch blocks in the b-tree 

   BR_BLK_LEN 

      useable space in a branch block 

   DEL_LF_ROWS 

      number of deleted leaf rows in the index 

   DEL_LF_ROWS_LEN 

      total length of all deleted rows in the index 

   DISTINCT_KEYS 

      number of distinct keys in the index 

   MOST_REPEATED_KEY 

      how many times the most repeated key is repeated 

   BTREE_SPACE 

      total space currently allocated in the b-tree 

   USED_SPACE 

      total space that is currently being used in the b-tree 

   PCT_USED 

      percent of space allocated in the b-tree that is being used 

   ROWS_PER_KEY 

      average number of rows per distinct key 

   BLKS_GETS_PER_ACCESS 

      Expected number of consistent mode block gets per row. This assumes that a row chosen at random from the table is being searched for using the index 

   PRE_ROWS 

      number of prefix rows (values in the index) 

   PRE_ROWS_LEN 

      sum of lengths of all prefix rows 

   OPT_CMPR_COUNT 

      optimal prefix compression count for the index