Does context cancellation cancel the underlying query?

[knadh]

ctx, cancel := context.WithCancel(context.Background())

// Cancel 5 seconds in.
go func() {
	time.Sleep(time.Second * 5)
  	cancel()
}()

// This query should take 10 seconds to return.
rows, err := dbt.db.QueryContext(ctx, "SELECT v, SLEEP(10) FROM test LIMIT 1")
fmt.Println(rows, err)

After reading #496 and #608, I was under the impression that in the above example, the underlying query would get canceled mid-execution, but that doesn't seem to be the case. It still takes 10 seconds to return (and the query shows in MySQL process list), albeit with the error sql: Rows are closed. Does this mean that the driver isn't actually able to cancel the underlying query running on the server?

[shogo82148]

Hi, I'm the author of #608.

Does this mean that the driver isn't actually able to cancel the underlying query running on the server?

Yes, my implement doesn't kill the query running on the server.
It is still on TODO status.

mysql/driver_go18_test.go

Line 270 in 9181e3a

if v != 1 { // TODO: need to kill the query, and v should be 0.

[methane]

FYI, you can limit query execution time via hint.
https://dev.mysql.com/doc/refman/5.7/en/optimizer-hints.html#optimizer-hints-execution-time

[knadh]

@shogo82148 @methane Thanks.

[arthurnn]

Are there any plans on fixing that TODO?

[jpcope]

Are there any plans on fixing that TODO?

#791

Looks like it is in a milestone btw. For others adding circuit breaking to services and find that queries persist in mysql, you may want to watch and react to these issues so the maintainers know there is interest.

Most of my peers expected this to work because they were more familiar with postgres where such workflows are known to work, are more easy to implement / are supported by the query session natively without making more connections.

For now I am documenting in my org that mysql is less friendly here and effective support for such a feature would warrant mysql server changing their connection interface.

A work around would be nice since we have so much using mysql at the moment. :-)

[pjebs]

https://medium.com/@rocketlaunchr.cloud/canceling-mysql-in-go-827ed8f83b30