database/sql: confusing MaxIdleClosed statistic

[AlekSi]

What version of Go are you using (go version)?

Both Go 1.11 and the current tip. MaxIdleClosed is not available in Go 1.10.

What did you do?

// use single database connection, never close it, always reuse
db.SetMaxOpenConns(1)
db.SetMaxIdleConns(1)
db.SetConnMaxLifetime(0)

log.Printf("%+v", db.Stats())

for i := 0; i < 10; i++ {
	if _, err := db.Exec("SELECT 1"); err != nil {
		log.Fatal(err)
	}
}

log.Printf("%+v", db.Stats())

https://github.com/AlekSi/go-sql-bugs/blob/master/issue27792_test.go

What did you expect to see?

{MaxOpenConnections:1 OpenConnections:0 InUse:0 Idle:0 WaitCount:0 WaitDuration:0s MaxIdleClosed:0 MaxLifetimeClosed:0}
{MaxOpenConnections:1 OpenConnections:1 InUse:0 Idle:1 WaitCount:0 WaitDuration:0s MaxIdleClosed:0 MaxLifetimeClosed:0}

What did you see instead?

{MaxOpenConnections:1 OpenConnections:0 InUse:0 Idle:0 WaitCount:0 WaitDuration:0s MaxIdleClosed:0 MaxLifetimeClosed:0}
{MaxOpenConnections:1 OpenConnections:1 InUse:0 Idle:1 WaitCount:0 WaitDuration:0s MaxIdleClosed:10 MaxLifetimeClosed:0}

By patching a driver I noticed that only a single connection is established in fact. But the statistic is wrong.

/cc @kardianos

[AlekSi]

Both Go 1.11 and the current tip. MaxIdleClosed is not available in Go 1.10.

btw, it is not mentioned on https://golang.org/doc/go1.11 at all. @dmitshur do you update changelogs after the fact? Should I create a separate issue?

[dmitshur]

btw, it is not mentioned on https://golang.org/doc/go1.11 at all. @dmitshur do you update changelogs after the fact? Should I create a separate issue?

The release notes only cover the most noteworthy changes or additions; it's not meant to be an exhaustive list of minor changes to the standard library. The package documentation is the place to find detailed information.

[bcmills]

CC @bradfitz @kardianos @kevinburke

[kardianos]

I'll look at this. I just haven't had time yet.

…

On Fri, Sep 21, 2018, 19:52 Bryan C. Mills ***@***.***> wrote: CC @bradfitz <https://github.com/bradfitz> @kardianos <https://github.com/kardianos> @kevinburke <https://github.com/kevinburke> — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#27792 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAuFsRPPzY4ineTHQn89tQkhGuab40TEks5udaXzgaJpZM4WzxuV> .

[bcmills]

Great, thank you!

[kardianos]

@AlekSi I see how this happens. I don't have a solution yet. I'll continue working on it.

[gopherbot]

Change https://golang.org/cl/138578 mentions this issue: database/sql: correctly report MaxIdleClosed stat

[jameshartig]

Could get cherry-picked into a 1.11.x release?

[ianlancetaylor]

@gopherbot please open backport to 1.11

[gopherbot]

Backport issue(s) opened: #28325 (for 1.11).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.