Sql服務器性能不是我所期望的

我有一個非常簡單的一個表查詢，需要幾秒鐘才能完成。我很困惑。當我從選擇頂端變爲50而不是200時，它變得更快。該表有大約一百萬行。Sql服務器性能不是我所期望的

我在所有提到的列上都有索引。

SELECT TOP 50 dbo.EmailDetails.Id, 
FROM dbo.EmailDetails WITH (NOLOCK) 
WHERE (dbo.EmailDetails.EmailSendStatus = 'NEEDTOSEND' OR 
    dbo.EmailDetails.EmailSendStatus = 'NEEDTOTEXT') AND 
    dbo.EmailDetails.EmailDetailsTopicId IS NOT NULL 
ORDER BY dbo.EmailDetails.EmailSendPriority, 
    dbo.EmailDetails.Id DESC

該計劃生成是：

和全DDL是：

CREATE TABLE dbo.EmailDetails (
     Id int IDENTITY(1, 1) NOT NULL, 
     AttendeesId int NOT NULL, 
     SponsorListContactId int NULL, 
     MessageUniqueId nvarchar(512) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     EmailSendStatus nvarchar(16) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     EmailSendStartTime datetime NULL, 
     EmailSendFinishTime datetime NULL, 
     EmailSendLogMessage nvarchar(max) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     Subject nvarchar(2048) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     BodyText nvarchar(max) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     SentDateTime datetime NULL, 
     EmailFrom nvarchar(128) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     EmailTo nvarchar(128) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     EmailDetailsTopicId int NULL, 
     EmailDetailsGuid uniqueidentifier NULL, 
     EmailReadCount int NULL, 
     EmailReadDate datetime NULL, 
     EmailSendStatusChange datetime NULL, 
     EmailSendPriority int NULL, 
     TextTo varchar(64) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, 
     CONSTRAINT EmailDetails_pk PRIMARY KEY CLUSTERED (Id) 
     WITH (
      PAD_INDEX = OFF, IGNORE_DUP_KEY = OFF, STATISTICS_NORECOMPUTE = OFF, 
      ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) 
    ) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_AttendeesIds_idx ON dbo.EmailDetails 
     (AttendeesId) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_idx ON dbo.EmailDetails 
     (EmailDetailsGuid) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_idx2 ON dbo.EmailDetails 
     (EmailDetailsTopicId) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_idx3 ON dbo.EmailDetails 
     (SentDateTime) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_priority_status_idx4 ON dbo.EmailDetails 
     (EmailSendPriority, EmailSendStatus) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_SentStatus_idx ON dbo.EmailDetails 
     (EmailSendStatus) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_topicid_attendeeid ON dbo.EmailDetails 
     (EmailDetailsTopicId, AttendeesId) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO 

    CREATE NONCLUSTERED INDEX EmailDetails_topicid_sponsorcontactid_idx ON dbo.EmailDetails 
     (EmailDetailsTopicId, SponsorListContactId) 
    WITH (
     PAD_INDEX = OFF, 
     DROP_EXISTING = OFF, 
     STATISTICS_NORECOMPUTE = OFF, 
     SORT_IN_TEMPDB = OFF, 
     ONLINE = OFF, 
     ALLOW_ROW_LOCKS = ON, 
     ALLOW_PAGE_LOCKS = ON) 
    ON [PRIMARY] 
    GO

來源

2016-03-24 Peter Kellner

你有關於它的具體問題嗎？ – B540Glenn

你知道查詢計劃是什麼嗎？導出IT（.sqlplan），然後我們可以提供幫助。 – TomTom

更快在200只是可能在內存中的行/索引。 50與200仍然需要排序。 – Paparazzi

在使用SELECT TOP x與ORDER BY一起一般建議，以確保相同的結果，每一個時間，ORDER BY將排序整個結果集，然後只有TOP x被採取f rom它。

我想知道你會看到如果你做SELECT COUNT(*)而不是SELECT TOP x：可能是一個相當高的數字？

雖然使用索引保證快速排序，但有沒有索引涵蓋了此查詢的確切ORDER BY。最重要的是，獲取WHERE和SELECT子句的字段需要進入可能遍佈磁盤的數據頁。爲了優化這個查詢，你可以將WHERE-和ORDER BY-和SELECT-字段添加到一個新的索引（按照這個順序），當然沒有重複。它會產生一個相當大的索引，這可能會減慢插入/更新速度，但也會使SELECT速度非常快，因爲只需使用索引即可滿足整個查詢，而無需進入數據頁。

來源

2016-03-24 16:51:41

謝謝大家的意見。當我回到我的辦公桌後，我會公佈計劃，並進行計數（*）測試。 –

做select count（*）非常快（即時），所以我認爲這不是索引問題。當我減少我檢索的列數時，它變得越來越快。我認爲這意味着我的數據必須散佈在磁盤周圍？無論如何，讓所有的最後條目彼此接近？最高紀錄總是我剛剛插入的10或20萬。 –

count（\ *）的值表示ORDER BY在可以採用TOP x之前必須完成的工作量，特別是如果沒有包含ORDER BY字段的單個索引。 count（\ *）本身的速度本身並不相關，如果請求count（\ *）並且沒有其他字段，則甚至有可能跳過ORDER BY。更重要的是如我所指出的那樣創建一個或多或少的索引。 –

Sql服務器性能不是我所期望的

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