Bizim uygulamada, kullanıcıların çok sayıda kayıt (10-20 milyon) üzerinden sayfa yazabilirsiniz bir ızgara var. Izgara, birkaç sütunda (20+) artan ve azalan sırada sıralamayı destekler. Değerlerin birçoğu da benzersiz değildir ve bu nedenle uygulama aynı zamanda satırların her zaman aynı sayfada görünmesini sağlamak için kimliğe göre bir bağlayıcı olarak sıralar. Örnek olarak, kullanıcı widget boyutuna göre (en büyüğü ile başlayarak) sıralamak isterse, uygulama şöyle görünen bir sorgu oluşturur:
SELECT TOP 30
* -- (Pretend that there is a list of columns here)
FROM Test
-- WHERE widgetSize > 100
ORDER BY
widgetSize DESC,
id ASC
Bu sorgunun çalıştırılması yaklaşık 15 saniye sürer (önbelleğe alınmış verilerle), maliyetin büyük bir kısmı widgetSize ile ~ 1.3m satır sıralaması gibi görünür. Bu sorguyu ayarlamak WHERE
için sadece en büyük widgetSizes (yukarıdaki sorguda yorumladı) ile sınırlı bir cümle eklerseniz , sorgu sadece ~ 800ms alır (ilk 50.000 sonuçların tümü bir widget boyutu> 100) olduğunu keşfetti .
WHERE
Madde içermeyen sorgu neden bu kadar yavaş? WidgetSize sütunundaki istatistikleri kontrol ettim ve en iyi 739 satırın bir WidgetSize> 506 olduğunu gösteriyorlar. Yalnızca 30 satır gerektiği için SQL sunucusu bu bilgileri yalnızca bir widget boyutuna sahip satırları sıralaması gerektiğini saptamak için kullanamaz. hangisi büyük?
Ben bir dizin ekleyerek bu belirli sorgu daha hızlı gerçekleştirmek yapabilir biliyorum widgetSize
veid
ancak bu endeks bu özel senaryoda sadece yararlıdır ve (örneğin) kullanıcı sıralama yönünü tersine çevirir eğer değersiz hale gelir. Bu tablo birçok ek sütun içerir ve her dizin büyüktür (~ 200mb), bu yüzden olası her sıralama düzeni için bir dizin eklemeyi göze alamam.
Her olası sıralama düzeni için bir dizin eklemeden gerçekleştirmek için bu sorguları sorgu alabilirsiniz bir yolu var mı? (kullanıcı 20'den fazla sütundan herhangi birine göre sıralayabilir)
Aşağıdaki komut dosyası yukarıdaki tabloyu oluşturur ve bazı temsili verilerle doldurur. Tablo, gerçek tablodan çok daha dar, ancak yine de gördüğüm performansı gösteriyor. Bilgisayarımda nerede yan tümcesi ile sorgu ~ 200ms alırken nerede yan tümcesi olmayan sorgu ~ 800ms alır.
Uyarı: Bu komut dosyasını çalıştırdıktan sonra ortaya çıkan veritabanı boyutu ~ 2Gb'dir.
CREATE TABLE Test
(
id INT NOT NULL IDENTITY(1,1) PRIMARY KEY,
widgetSize INT NOT NULL
)
CREATE TABLE #Data
(
widgetSize INT NOT NULL,
recordCount INT NOT NULL
)
INSERT INTO #Data (widgetSize, recordCount)
VALUES
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DECLARE c CURSOR FOR
SELECT widgetSize, recordCount FROM #Data
OPEN c
DECLARE @widgetSize INT
DECLARE @rowCount INT
FETCH NEXT FROM c INTO @widgetSize, @rowCount
WHILE @@FETCH_STATUS = 0
BEGIN
;WITH cte AS
(
SELECT rowNumber = 1
UNION ALL
SELECT rowNumber + 1
FROM cte
WHERE rowNumber < @rowCount
)
INSERT INTO Test
(
widgetSize
)
SELECT
@widgetSize
FROM cte
OPTION (MAXRECURSION 0)
FETCH NEXT FROM c INTO @widgetSize, @rowCount
END
CLOSE c
DEALLOCATE c
DROP TABLE #Data
CREATE STATISTICS WidgetSize
ON Test (WidgetSize) WITH FULLSCAN
(id, widgetSize)
? Arama sırası ASC/DESC
dizinden döndürülürse, önden geriye doğru okunursa, kullanılmaz hale gelir.
CREATE CLUSTERED INDEX CIX_id_widgetSize ON Test (id, widgetSize)
13773285 rows < 100
ve yalnızca 65717 rows > 100
, bu nedenle sorgulanan satırları büyük ölçüde sınırlandırırsınız WHERE
. Filtreleyebileceğiniz başka bir değer var mı? İşletmeniz varsa, tabloyu bölümlere ayırmayı düşünebilirsiniz.
id
vewidgetsize
?