sqlite_stat1表的说明

Question

我正在尝试诊断特定查询对SQLite的速度慢的原因.似乎有很多关于查询优化器如何工作的信息,但关于如何实际诊断问题的信息很少.

特别是,当我分析数据库时,我得到了预期的sqlite_stat1表,但我不知道stat列告诉我什么.示例行是:

MyTable,ix_id,25112 1 1 1 1

"25112 1 1 1 1"究竟是什么意思？

作为一个更广泛的问题,有没有人有关于诊断SQLite查询性能的最佳工具和技术的任何好资源？

谢谢

Answer 1

来自analyze.c:

/* Store the results.  
**
** The result is a single row of the sqlite_stmt1 table.  The first
** two columns are the names of the table and index.  The third column
** is a string composed of a list of integer statistics about the
** index.  The first integer in the list is the total number of entires
** in the index.  There is one additional integer in the list for each
** column of the table.  This additional integer is a guess of how many
** rows of the table the index will select.  If D is the count of distinct
** values and K is the total number of rows, then the integer is computed
** as:
**
**        I = (K+D-1)/D
**
** If K==0 then no entry is made into the sqlite_stat1 table.  
** If K>0 then it is always the case the D>0 so division by zero
** is never possible.