Estatísticas de tempo

Melhorando o Desempenho de Consultas no SQL Server

Dean Smith

Founder, Atamai Analytics

SQL Server Management Studio

Tela de abertura do SQL Server Management Studio

STATISTICS TIME no SSMS

SELECT UNStatisticalRegion, 
        CountryName,
        Capital
FROM Nations
WHERE Capital IN 
        (SELECT CityName 
        FROM Cities)
            AND Capital IN 
                (SELECT CityName 
                    FROM Cities 
                    WHERE Pop2017 > 1000000);

STATISTICS TIME - o comando informa, em milissegundos, o tempo para analisar, compilar e executar uma consulta.

SQL Server parse and compile time: 
   CPU time = 16 ms, elapsed time = 21 ms.

(88 rows affected)

 SQL Server Execution Times:
   CPU time = 390 ms,  elapsed time = 382 ms.

SQL Server Execution Times

 SQL Server Execution Times:
   CPU time = 390 ms,  elapsed time = 382 ms.

CPU time: tempo gasto pelos processadores do servidor para processar a consulta
Elapsed time: duração total da consulta

Exemplo: consulta 1

SELECT UNStatisticalRegion, 
       CountryName,
       Capital
FROM Nations
WHERE Capital IN 
        (SELECT CityName -- 1st sub-query
        FROM Cities) 
            AND Capital IN 
                (SELECT CityName -- 2nd sub-query
                 FROM Cities 
                 WHERE Pop2017 > 1000000);

Exemplo: consulta 1

SET STATISTICS TIME ON

SELECT UNStatisticalRegion, 
       CountryName,
       Capital
FROM Nations
WHERE Capital IN 
        (SELECT CityName -- 1st sub-query
        FROM Cities) 
            AND Capital IN 
                (SELECT CityName -- 2nd sub-query
                 FROM Cities 
                 WHERE Pop2017 > 1000000);

SQL Server Execution Times:
   CPU time = 391 ms,  elapsed time = 381 ms.

Exemplo: consulta 2

SELECT UNStatisticalRegion, 
       CountryName,
       Capital 
FROM Nations n
WHERE EXISTS 
    (SELECT 1 
     FROM  Cities c 
     WHERE n.Capital = c.CityName
        AND Pop2017 > 1000000);

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 2 ms.

Exemplo: consulta 2

SELECT UNStatisticalRegion, 
       CountryName,
       Capital 
FROM Nations n
WHERE EXISTS 
    (SELECT 1 
     FROM  Cities c 
     WHERE n.Capital = c.CityName
        AND Pop2017 > 1000000);

SET STATISTICS TIME OFF

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 2 ms.

Comparando consultas

Primeira consulta com duas subconsultas

SELECT UNStatisticalRegion, 
       CountryName,
       Capital
FROM Nations
WHERE Capital IN 
        (SELECT CityName 
        FROM Cities)
            AND Capital IN 
                (SELECT CityName 
                 FROM Cities 
                 WHERE Pop2017 > 1000000);

SQL Server Execution Times:
   CPU time = 391 ms,  elapsed time = 381 ms.

Segunda consulta usando EXISTS

SELECT UNStatisticalRegion, 
       CountryName,
       Capital 
FROM Nations n
WHERE EXISTS 
    (SELECT 1 
     FROM  Cities c 
     WHERE n.Capital = c.CityName
        AND Pop2017 > 1000000);

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 2 ms.

Elapsed time vs. CPU time

Elapsed time

Pode variar ao analisar estatísticas de tempo de consulta
Melhor medida para identificar a consulta mais rápida

CPU time

Deve variar pouco ao analisar estatísticas de tempo
Pode não ser útil se os processadores do servidor executarem em paralelo

Calculando a média

Não dependa de uma única medição; calcule a média.

elapsed time = 2032 ms.

elapsed time = 2060 ms.

elapsed time = 1915 ms.

elapsed time = 4009 ms.

elapsed time = 3511 ms.

Average elapsed time = 2705 ms.

Vamos praticar!

Melhorando o Desempenho de Consultas no SQL Server