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database/sql: Transaction was timeout and rollback but the query was executed on db #32942

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namnd95 opened this issue Jul 4, 2019 · 6 comments
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@namnd95
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@namnd95 namnd95 commented Jul 4, 2019

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

go version go1.12 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/nguyendn/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/nguyendn/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go-1.12"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.12/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build871815186=/tmp/go-build -gno-record-gcc-switches"

What did you do?

We begin a db transaction with a context timeout and exec a sql query after that.
If the db transaction is timeout, during extreme condition, the transaction was rollback because of timeout but the query was executed successfully and the data persists to db.

Code:

var err error
var tx *sql.Tx
ctx, cancelFunc := context.WithTimeout(context.Background(), time.Nanosecond*1000000)
defer cancelFunc()
tx, err = db.BeginTx(ctx, nil) // begin with a very short timeout to reproduce the error
_, err = tx.Exec("insert into test values()") // transaction timeout and auto rollback, but the query can be executed without errors
tx.Rollback() // err: sql: transaction has already been committed or rolled back

MySQL logs

279 Connect	root@localhost on test using TCP/IP
279 Query	START TRANSACTION
279 Query	ROLLBACK
279 Query	insert into test values()

What did you expect to see?

The query execution after rollback should return error

What did you see instead?

The query execution was committed to db

Cause

main go routine:

we have entered this function tx.Exec() -> tx.ExecContext() -> db.ExecDC() but haven't executed the query yet

	defer func() {
		release(err)
	}()
	execerCtx, ok := dc.ci.(driver.ExecerContext)
	var execer driver.Execer
	if !ok {
		execer, ok = dc.ci.(driver.Execer)
	}
	// WE ARE CURRENTLY AT THIS LINE
	if ok {
		var nvdargs []driver.NamedValue
		var resi driver.Result
		withLock(dc, func() {
			nvdargs, err = driverArgsConnLocked(dc.ci, nil, args)
			if err != nil {
				return
			}
			resi, err = ctxDriverExec(ctx, execerCtx, execer, query, nvdargs)
		})
		if err != driver.ErrSkip {
			if err != nil {
				return nil, err
			}
			return driverResult{dc, resi}, nil
		}
	}

awaitDone go routine:

we have entered tx.awaitDone() -> tx.rollback(true) -> tx.txi.Rollback()

	if !atomic.CompareAndSwapInt32(&tx.done, 0, 1) {
		return ErrTxDone
	}
	var err error
	withLock(tx.dc, func() {      
		err = tx.txi.Rollback()    // THIS CAN BE EXECUTED SUCCESSFULLY ALTHOUGH STILL HAVE ACTIVE QUERY
	})
	if err != driver.ErrBadConn {
		tx.closePrepared()
	}
	if discardConn {
		err = driver.ErrBadConn
	}
	tx.close(err) // We only check tx.closemu lock here
	return err

We have the lock tx.closemu to ensure there aren't any active queries in the transaction, but we already rollback the transaction before checking the availability of the lock.
I suggest checking this lock in tx.rollback and tx.Commit function directly instead of tx.Close

@kardianos kardianos self-assigned this Jul 4, 2019
@methane
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@methane methane commented Nov 11, 2019

Is this issue same to #34775?

@namnd95
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@namnd95 namnd95 commented Nov 15, 2019

This issue should have the same cause with #34775

@gopherbot
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@gopherbot gopherbot commented Jan 24, 2020

Change https://golang.org/cl/216240 mentions this issue: database/sql: prevent Tx statement from committing after rollback

@gopherbot gopherbot closed this in d8f0a22 Apr 20, 2020
@gopherbot
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@gopherbot gopherbot commented Jul 11, 2020

Change https://golang.org/cl/242101 mentions this issue: [release-branch.go1.14] database/sql: backport 3 Tx rollback related CLs

@gopherbot
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@gopherbot gopherbot commented Jul 11, 2020

Change https://golang.org/cl/242102 mentions this issue: [release-branch.go1.14] database/sql: backport 3 Tx rollback related CLs

@gopherbot
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@gopherbot gopherbot commented Jul 15, 2020

Change https://golang.org/cl/242522 mentions this issue: [release-branch.go1.13] database/sql: backport 5 Tx rollback related CLs

gopherbot pushed a commit that referenced this issue Jul 16, 2020
Manually backported the subject CLs, because of lack of
Gerrit "forge-author" permissions, but also because the prior
cherry picks didn't apply cleanly, due to a tight relation chain.

The backport comprises of:
* CL 174122
* CL 216197
* CL 223963
* CL 216240
* CL 216241

Note:
Due to the restrictions that we cannot retroactively
introduce API changes to Go1.13.13 that weren't in Go1.13, the Conn.Validator
interface (from CL 174122, CL 223963) isn't exposed, and drivers will just be
inspected, for if they have an IsValid() bool method implemented.

For a description of the content of each CL:

* CL 174122:
database/sql: process all Session Resets synchronously

Adds a new interface, driver.ConnectionValidator, to allow
drivers to signal they should not be used again,
separatly from the session resetter interface.
This is done now that the session reset is done
after the connection is put into the connection pool.

Previous behavior attempted to run Session Resets
in a background worker. This implementation had two
problems: untested performance gains for additional
complexity, and failures when the pool size
exceeded the connection reset channel buffer size.

* CL 216197:
database/sql: check conn expiry when returning to pool, not when handing it out

With the original connection reuse strategy, it was possible that
when a new connection was requested, the pool would wait for an
an existing connection to return for re-use in a full connection
pool, and then it would check if the returned connection was expired.
If the returned connection expired while awaiting re-use, it would
return an error to the location requestiong the new connection.
The existing call sites requesting a new connection was often the last
attempt at returning a connection for a query. This would then
result in a failed query.

This change ensures that we perform the expiry check right
before a connection is inserted back in to the connection pool
for while requesting a new connection. If requesting a new connection
it will no longer fail due to the connection expiring.

* CL 216240:
database/sql: prevent Tx statement from committing after rollback

It was possible for a Tx that was aborted for rollback
asynchronously to execute a query after the rollback had completed
on the database, which often would auto commit the query outside
of the transaction.

By W-locking the tx.closemu prior to issuing the rollback
connection it ensures any Tx query either fails or finishes
on the Tx, and never after the Tx has rolled back.

* CL 216241:
database/sql: on Tx rollback, retain connection if driver can reset session

Previously the Tx would drop the connection after rolling back from
a context cancel. Now if the driver can reset the session,
keep the connection.

* CL 223963
database/sql: add test for Conn.Validator interface

This addresses comments made by Russ after
https://golang.org/cl/174122 was merged. It addes a test
for the connection validator and renames the interface to just
"Validator".

Updates #31480
Updates #32530
Updates #32942
Updates #34775
Fixes #40205

Change-Id: I6d7307180b0db0bf159130d91161764cf0f18b58
Reviewed-on: https://go-review.googlesource.com/c/go/+/242522
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
gopherbot pushed a commit that referenced this issue Jul 16, 2020
Manually backported the subject CLs, because of lack of
Gerrit "forge-author" permissions, but also because the prior
cherry picks didn't apply cleanly, due to a tight relation chain.

The backport comprises of:
* CL 174122
* CL 216197
* CL 223963
* CL 216240
* CL 216241

Note:
Due to the restrictions that we cannot retroactively
introduce API changes to Go1.14.6 that weren't in Go1.14, the Conn.Validator
interface (from CL 174122, CL 223963) isn't exposed, and drivers will just be
inspected, for if they have an IsValid() bool method implemented.

For a description of the content of each CL:

* CL 174122:
database/sql: process all Session Resets synchronously

Adds a new interface, driver.ConnectionValidator, to allow
drivers to signal they should not be used again,
separatly from the session resetter interface.
This is done now that the session reset is done
after the connection is put into the connection pool.

Previous behavior attempted to run Session Resets
in a background worker. This implementation had two
problems: untested performance gains for additional
complexity, and failures when the pool size
exceeded the connection reset channel buffer size.

* CL 216197:
database/sql: check conn expiry when returning to pool, not when handing it out

With the original connection reuse strategy, it was possible that
when a new connection was requested, the pool would wait for an
an existing connection to return for re-use in a full connection
pool, and then it would check if the returned connection was expired.
If the returned connection expired while awaiting re-use, it would
return an error to the location requestiong the new connection.
The existing call sites requesting a new connection was often the last
attempt at returning a connection for a query. This would then
result in a failed query.

This change ensures that we perform the expiry check right
before a connection is inserted back in to the connection pool
for while requesting a new connection. If requesting a new connection
it will no longer fail due to the connection expiring.

* CL 216240:
database/sql: prevent Tx statement from committing after rollback

It was possible for a Tx that was aborted for rollback
asynchronously to execute a query after the rollback had completed
on the database, which often would auto commit the query outside
of the transaction.

By W-locking the tx.closemu prior to issuing the rollback
connection it ensures any Tx query either fails or finishes
on the Tx, and never after the Tx has rolled back.

* CL 216241:
database/sql: on Tx rollback, retain connection if driver can reset session

Previously the Tx would drop the connection after rolling back from
a context cancel. Now if the driver can reset the session,
keep the connection.

* CL 223963
database/sql: add test for Conn.Validator interface

This addresses comments made by Russ after
https://golang.org/cl/174122 was merged. It addes a test
for the connection validator and renames the interface to just
"Validator".

Updates #31480
Updates #32530
Updates #32942
Updates #34775
Fixes #39101

Change-Id: I043d2d724a367588689fd7d6f3cecb39abeb042c
Reviewed-on: https://go-review.googlesource.com/c/go/+/242102
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
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