SQL Server：在填充因子小於100％後預計有多少指數增長

Question

我在填充因子爲100％的數據庫中有大約250 GB的索引。爲了提高性能，我想將填充因子降低到95％。

因此，在將填充因子應用於我的索引之前，我想知道在應用95％填充因子後索引大小將增長多少。

我期望的是，索引尺寸總數的5％會增長是正確的嗎？

Answer 1

我在想這個昨晚上和邏輯上它將使意義，所以我決定來測試它：

- 創建測試表

CREATE TABLE TableIndexTest (id INT, id2 INT, var VARCHAR(100)) 

--Populate一些有意義的數據

DECLARE @num  INT = 1000000 
DECLARE @var  VARCHAR(100) = 'ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ' 
DECLARE @num2 INT = 1000000 
DECLARE @iter INT = 1000000 
DECLARE @num_curr INT = 1 
WHILE (@num_curr <= @num) 
BEGIN 
    INSERT TableIndexTest (id, id2, var) SELECT @num_curr, @num_curr, @var 
    SELECT @num_curr = @num_curr + 1 
END 

- 用fillfactor創建一些索引

CREATE NONCLUSTERED INDEX ix_test_fillfactor100 ON TableIndexTest ([id], [id2], [var]) 
CREATE NONCLUSTERED INDEX ix_test_fillfactor90 ON TableIndexTest ([id], [id2], [var]) WITH (FILLFACTOR = 90) 
CREATE NONCLUSTERED INDEX ix_test_fillfactor80 ON TableIndexTest ([id], [id2], [var]) WITH (FILLFACTOR = 80) 
CREATE NONCLUSTERED INDEX ix_test_fillfactor70 ON TableIndexTest ([id], [id2], [var]) WITH (FILLFACTOR = 70) 
CREATE NONCLUSTERED INDEX ix_test_fillfactor60 ON TableIndexTest ([id], [id2], [var]) WITH (FILLFACTOR = 60) 
CREATE NONCLUSTERED INDEX ix_test_fillfactor50 ON TableIndexTest ([id], [id2], [var]) WITH (FILLFACTOR = 50) 

- 檢查索引大小

SELECT 
    i.name AS IndexName, 
    SUM(s.used_page_count) * 8 AS IndexSizeKB 
FROM sys.dm_db_partition_stats AS s 
JOIN sys.indexes AS i ON s.[object_id] = i.[object_id] AND s.index_id = i.index_id 
WHERE s.[object_id] = OBJECT_ID('TableIndexTest') 
GROUP BY i.name 
ORDER BY SUM(s.used_page_count) * 8; 

預期結果將是，該指數將填充因子設置爲50將不填充因子集索引的一半大小（Server的默認爲0，因此將基本上100） 。

結果：

IndexName    IndexSizeKB 
ix_test_fillfactor100   52008 
ix_test_fillfactor90   57176 
ix_test_fillfactor80   64480 
ix_test_fillfactor70   73952 
ix_test_fillfactor60   85752 
ix_test_fillfactor50   103328 

所以填充因子50 * 2 = 104016時預計將103328但考慮到該指數的最後一頁可能只有它的1行，我認爲它非常接近這樣你可以安全地使用這種計算