如何提高LINQ的性能？

Question

更新感謝@usr我只需更改即可將此縮短至~3秒

.Select(
     log => log.OrderByDescending(
     d => d.DateTimeUTC
     ).FirstOrDefault()
)

至

    .Select(
     log => log.OrderByDescending(
     d => d.Id
     ).FirstOrDefault()
)

我有一個包含兩個表的數據庫 - 日志和收集器 - 我正在使用實體框架來讀取。 有86個收集器記錄，每個記錄有50000+對應的日志記錄。

我希望獲得每個收集器的最新日志記錄，這可以通過此SQL輕松完成

SELECT CollectorLogModels_1.Status, CollectorLogModels_1.NumericValue,
    CollectorLogModels_1.StringValue, CollectorLogModels_1.DateTimeUTC,
    CollectorSettingsModels.Target, CollectorSettingsModels.TypeName 
FROM
    (SELECT CollectorId, MAX(Id) AS Id 
     FROM CollectorLogModels GROUP BY CollectorId) AS RecentLogs 
INNER JOIN CollectorLogModels AS CollectorLogModels_1 
   ON RecentLogs.Id = CollectorLogModels_1.Id 
      INNER JOIN CollectorSettingsModels 
          ON CollectorLogModels_1.CollectorId = CollectorSettingsModels.Id

這需要大約2秒的時間來執行。

我能用LINQ得到的最接近的是以下內容

var logs = context.Logs.Include(co => co.Collector)
                .GroupBy(
                    log => log.CollectorId, log => log
                )
                .Select(
                    log => log.OrderByDescending(
                        d => d.DateTimeUtc
                        ).FirstOrDefault()
                )
                .Join(
                    context.Collectors,
                    (l => l.CollectorId),
                    (c => c.Id),
                    (l, c) => new
                    {
                        c.Target,
                        DateTimeUTC = l.DateTimeUtc,
                        l.Status,
                        l.StringValue,
                        CollectorName = c.TypeName
                    }
                ).OrderBy(
                    o => o.Target
                ).ThenBy(
                    o => o.CollectorName
                )
                ;

這會產生我想要的結果，但需要大約35秒才能執行。

這成為以下SQL

SELECT 
[Distinct1].[CollectorId] AS [CollectorId], 
[Extent3].[Target] AS [Target], 
[Limit1].[DateTimeUtc] AS [DateTimeUtc], 
[Limit1].[Status] AS [Status], 
[Limit1].[StringValue] AS [StringValue], 
[Extent3].[TypeName] AS [TypeName]
FROM    (SELECT DISTINCT 
    [Extent1].[CollectorId] AS [CollectorId]
    FROM [dbo].[CollectorLogModels] AS [Extent1] ) AS [Distinct1]
OUTER APPLY  (SELECT TOP (1) [Project2].[Status] AS [Status], [Project2].[StringValue] AS [StringValue], [Project2].[DateTimeUtc] AS [DateTimeUtc], [Project2].[CollectorId] AS [CollectorId]
    FROM ( SELECT 
        [Extent2].[Status] AS [Status], 
        [Extent2].[StringValue] AS [StringValue], 
        [Extent2].[DateTimeUtc] AS [DateTimeUtc], 
        [Extent2].[CollectorId] AS [CollectorId]
        FROM [dbo].[CollectorLogModels] AS [Extent2]
        WHERE [Distinct1].[CollectorId] = [Extent2].[CollectorId]
    )  AS [Project2]
    ORDER BY [Project2].[DateTimeUtc] DESC ) AS [Limit1]
INNER JOIN [dbo].[CollectorSettingsModels] AS [Extent3] ON [Limit1].[CollectorId] = [Extent3].[Id]
ORDER BY [Extent3].[Target] ASC, [Extent3].[TypeName] ASC

如何才能使性能更接近單獨使用SQL可實現的性能？

Answer 1

在原始SQL中，您可以從與MAX（ID）不同的行中選擇一個集合DateTimeUTC。 那可能是個錯誤。 EF沒有那個問題。 它在語義上不相同，這是一個更難的查詢。

如果您重寫EF查詢在結構上與SQL查詢相同，您將獲得相同的性能。 我在這里看不到EF不支持的任何內容。

用EF計算max(id)並加入。

Answer 2

我有完全相同的問題，我通過添加索引解決了它。

我的查詢需要45秒才能完成，我設法在不到一秒的時間內完成。