Question

I have a single SQL Server table with 10 different triggers that fire on the same INSERT and UPDATE.

Is there any performance advantage to consolidating the SQL inside the 10 triggers into a single trigger?

The single consolidated trigger would do the same thing as the 10 different triggers, but only one trigger would get fired instead of 10.

Thanks!

Update: Thanks for the great feedback. I updated my question to indicate that I am wondering about performance advantages. I didn’t think of the “absolute control over order” advantage. I am aware that these various triggers should be refactored at some point, but am wondering more about performance of one versus many triggers.

Answer 1

Consolidating triggers can make a huge performance boost. For example consider the following table, two triggers, and an update:

CREATE TABLE dbo.TriggerTest(ID INT NOT NULL PRIMARY KEY,
s INT NOT NULL)
GO
INSERT INTO dbo.TriggerTest(ID, s)
SELECT n, 1 FROM dbo.Numbers
WHERE n BETWEEN 1 AND 100000;
GO

CREATE TRIGGER TriggerTestNoSignChange
ON dbo.TriggerTest
AFTER UPDATE
AS
BEGIN
    IF EXISTS(SELECT * FROM INSERTED AS i JOIN DELETED AS d
    ON i.id = d.id WHERE sign(i.s)*sign(d.s)<0)
    BEGIN
        RAISERROR('s cannot change sign', 16, 1);
        ROLLBACK ;
    END
END
GO

CREATE TRIGGER TriggerTestNoBigChange
ON dbo.TriggerTest
AFTER UPDATE
AS
BEGIN
    IF EXISTS(SELECT * FROM INSERTED AS i JOIN DELETED AS d
    ON i.id = d.id WHERE ABS(i.s - d.s)>5)
    BEGIN
        RAISERROR('s cannot change by more than 5', 16, 1);
        ROLLBACK ;
    END
END
GO


UPDATE dbo.TriggerTest SET s=s+1
WHERE ID BETWEEN 1 AND 1000;

This update uses 1671 ms CPU and 4M reads. Let’s consolidate two triggers and rerun the update:

DROP TRIGGER TriggerTestNoSignChange;
DROP TRIGGER TriggerTestNoBigChange;
GO
CREATE TRIGGER TriggerTestNoBigChangeOrSignChange
ON dbo.TriggerTest
AFTER UPDATE
AS
BEGIN
    IF EXISTS(SELECT * FROM INSERTED AS i JOIN DELETED AS d
    ON i.id = d.id WHERE sign(i.s)*sign(d.s)<0 OR ABS(i.s - d.s)>5)
    BEGIN
        RAISERROR('s cannot change sign or change by more than 5', 16, 1);
        ROLLBACK ;
    END
END
GO


UPDATE dbo.TriggerTest SET s=s+1
WHERE ID BETWEEN 1 AND 1000;

The same update runs twice us fast. Big surprise. 😉