Re: Decrease time needed to CREATE INDEX and FOREIGN KEY on new table column which has all values NULL

On 2019-Jan-22, Denisa Cirstescu wrote:

> I am trying to add a new column to a really big table and to define an INDEX and a FOREIGN KEY on that new column using the following instructions:
>
> ALTER TABLE Employee ADD COLUMN DepartmentId INTEGER;
> CREATE INDEX IDX_Employee_DepartmentId ON Employee(DepartmentId);
> ALTER TABLE Employee ADD CONSTRAINT FK_Employee_Department FOREIGN KEY(DepartmentId) REFERENCES Department(DepartmentId);
>
> The table is huge and it takes a lot of time to add the INDEX and the FOREIGN KEY although all values are NULL.
> Considering that the new DepartmentId column is NULL for all rows at this point, is there a way to make the INDEX and FOREIGN KEY creation run faster?

The typical advice is to run CREATE INDEX CONCURRENTLY instead of plain
CREATE INDEX. Also, use "ADD CONSTRAINT ... NOT VALID;" instead, and
later do another ALTER TABLE ... VALIDATE CONSTRAINT. That decreases
the impact considerably in production scenarios.

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Álvaro Herrera https://www.2ndQuadrant.com/
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