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SQLServer自动更新统计信息的基本算法 - 站长搜索
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SQLServer自动更新统计信息的基本算法

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2022-09-23 16:50:50 转载来源: 网络整理/侵权必删

自动更新统计信息的基本算法是:·如果表格是在tempdb数据库表的基数是小于6,自动更新到表的每个六个修改。·如果表的基数是大于6,但小于或等于500,更新状态每500的修改

自动更新统计信息基本算法是:

· 如果表格是在 tempdb 数据库表的基数是小于 6,自动更新到表的每个六个修改。
· 如果表的基数是大于 6,但小于或等于 500,更新状态每 500 的修改。
· 如果基数大于 500,表为更新统计信息时(500 + 20%的表)发生了更改。
· 表变量为基数的更改不会触发自动更新统计信息。

注意:此严格意义上讲,SQL Server 计算基数为表中的行数。

注意:除了基数,该谓语的选择性也会影响 AutoStats 生成。这意味着该统计信息可能无法更新的 afer 每 500 修改基数是 < 500 或更改的每个 20%的基数好像 > 500。比例因子(值的范围从 1 到 4、 1 和 4 之间)上生成根据选择性,这一因素的更改从算法获得数的乘积 AutoStats 生成所需的修改的实际数目。

在表的窗体中,可以summarised 以上算法:
_________________________________________________________________________________
Table Type | Empty Condition | Threshold WhenEmpty |Threshold When Not Empty
_________________________________________________________________________________
Permanent | < 500 rows | # ofChanges >= 500 | # of Changes >=500 + (20% of Cardinality)
___________________________________________________________________________
Temporary | < 6 rows | # ofChanges >= 6 | # of Changes >=500 + (20% of Cardinality)
___________________________________________________________________________
Table
Variables | Change in cardinality does not affectAutoStats generation.
___________________________________________________________________________


作者 SmithLiu328

标签: SQLServer 自动 更新 统计 信息 基本 算法


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