[筆記]statistics資訊的收集

Statistics generated include the following:
1，Table statistics
– Number of rows
– Number of blocks
– Average row length
2，Column statistics
– Number of distinct values (NDV) in column
– Number of nulls in column
– Data distribution (histogram)
3，Index statistics
– Number of leaf blocks
– Levels
– Clustering factor
4，System statistics
– I/O performance and utilization
– CPU performance and utilization[@more@]

1，表中塊的數目，索引深度，從ROOT塊到它的葉塊。這些都是計算的很準確的。

2，ORACLE推薦在使用dbms_stat收集的時候,estimate_percent引數使用auto_sample_size 這個去自動讓ORACLE根據伺服器情況定義收集比例：

EXECUTE DBMS_STATS.GATHER_SCHEMA_STATS('OE',DBMS_STATS.AUTO_SAMPLE_SIZE);

3，