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database/sql: confusing MaxIdleClosed statistic #27792

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AlekSi opened this issue Sep 21, 2018 · 10 comments
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database/sql: confusing MaxIdleClosed statistic #27792

AlekSi opened this issue Sep 21, 2018 · 10 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Milestone
Go1.12

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@AlekSi
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AlekSi commented Sep 21, 2018 •
edited

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
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AlekSi commented Sep 21, 2018

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
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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
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bcmills commented Sep 22, 2018

CC @bradfitz @kardianos @kevinburke

@bcmills bcmills added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Sep 22, 2018
@bcmills bcmills added this to the Go1.12 milestone Sep 22, 2018
@kardianos
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kardianos commented Sep 22, 2018 via email

@bcmills
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bcmills commented Sep 22, 2018

Great, thank you!

@kardianos
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kardianos commented Sep 23, 2018 •
edited

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

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

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

@ianlancetaylor
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@gopherbot please open backport to 1.11

@gopherbot
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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.

@gopherbot gopherbot mentioned this issue Oct 22, 2018
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