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database/sql: driver.ErrBadConn masked in *sql.DB.Begin #4433

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gopherbot opened this issue Nov 25, 2012 · 7 comments
Closed

database/sql: driver.ErrBadConn masked in *sql.DB.Begin #4433

gopherbot opened this issue Nov 25, 2012 · 7 comments
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@gopherbot
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by jane.chalfant:

What steps will reproduce the problem?

1. Encounter driver.ErrBadConn when calling driver.Conn.Begin from within *sql.DB.begin
2. Observe that *sql.DB.Begin does not call *sql.DB.begin again up to 10 times, as
driver.ErrBadConn != fmt.Errorf("sql: failed to Begin transaction: %v",
driver.ErrBadConn)

What is the expected output?
Up to 9 subsequent attempts to call *sql.DB.begin()

What do you see instead?
Immediate failure after driver.ErrBadConn is encountered.

Which compiler are you using (5g, 6g, 8g, gccgo)?
6g

Which operating system are you using?
Mac OS X 10.8.2

Which version are you using?  (run 'go version')
1.0.3

Please provide any additional information below.

It appears to me that there database/sql intends to retry many driver operations
(Prepare, Exec, Begin) up to 10 times if a driver.ErrBadConn is encountered. This retry
logic doesn't get applied in *sql.DB.Begin, as *sql.DB.begin will create a new, more
informative error which then causes "err != driver.ErrBadConn" to resolve to
true.

Consider the following code, if ci.Begin() returns driver.ErrBadConn:

func (db *DB) Begin() (*Tx, error) {
    var tx *Tx
    var err error
    for i := 0; i < 10; i++ {
        tx, err = db.begin()
        if err != driver.ErrBadConn {
            break
        }
    }
    return tx, err
}

func (db *DB) begin() (tx *Tx, err error) {
    ci, err := db.conn()
    if err != nil {
        return nil, err
    }
    txi, err := ci.Begin()
    if err != nil {
        db.putConn(ci, err)
        return nil, fmt.Errorf("sql: failed to Begin transaction: %v", err)
    }
    return &Tx{
        db:  db,
        ci:  ci,
        txi: txi,
    }, nil
}

Note that the error returned from db.begin() will not be driver.ErrBadConn, it will be
the result of this:

fmt.Errorf("sql: failed to Begin transaction: %v", driver.ErrBadConn)

One possible solution would be to return driver.ErrBadConn
@gopherbot
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Comment 1 by james.chalfant:

Awkwardly enough, I was signed in as the wrong google user when I entered this (Jane
Chalfant rather than James Chalfant)

@gopherbot
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Comment 2 by james.chalfant:

Diff attached with proposed solution. 
If the this seems appropriate, I've also created a change at
http://golang.org/cl/6845094 that I can mail for review.

Attachments:

  1. sql.go.diff (336 bytes)

@rsc
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rsc commented Dec 9, 2012

Comment 3:

Brad, want to look at the CL?

Labels changed: added priority-later, removed priority-triage.

Owner changed to @bradfitz.

Status changed to Accepted.

@rsc
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rsc commented Dec 10, 2012

Comment 4:

Labels changed: added size-m.

@bradfitz
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Comment 5:

Seems good. Sorry for the delay.
Can you sign the CLA and then hg mail 6845094?

@gopherbot
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Comment 6 by james.chalfant:

I've signed the CLA online and done ''hg mail 6845094".

@bradfitz
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Comment 7:

This issue was closed by revision 309eae1.

Status changed to Fixed.

@rsc rsc added this to the Go1.1 milestone Apr 14, 2015
@rsc rsc removed the go1.1 label Apr 14, 2015
@golang golang locked and limited conversation to collaborators Jun 24, 2016
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