执行后事务保持在pg_stat_activity状态

Question

I'm quite new to both PostgreSQL and golang. Mainly, I am trying to understand the following:

• Why did I need the Commit statement to close the connection and the other two Close calls didn't do the trick?
• Would also appreciate pointers regarding the right/wrong way in which I'm going about working with cursors.

---

In the following function, I'm using gorp to make a CURSOR, query my Postgres DB row by row and write each row to a writer function:

func(txn *gorp.Transaction, 
     q string,
     params []interface{}, 
     myWriter func([]byte, error)) {

    cursor := "DECLARE GRABDATA NO SCROLL CURSOR FOR " + q
    _, err := txn.Exec(cursor, params...)
    if err != nil {
        myWriter(nil, err)
        return
    }

    rows, err := txn.Query("FETCH ALL in GRABDATA")
    if err != nil {
        myWriter(nil, err)
        return
    }

    defer func() {
        if _, err := txn.Exec("CLOSE GRABDATA"); err != nil {
            fmt.Println("Error while closing cursor:", err)
        }
        if err = rows.Close(); err != nil {
            fmt.Println("Error while closing rows:", err)
        } else {
            fmt.Println("\n\n\n Closed rows without error", "\n\n\n")
        }
        if err = txn.Commit(); err != nil {
            fmt.Println("Error on commit:", err)
        }
    }()

    pointers := make([]interface{}, len(cols))
    container := make([]sql.NullString, len(cols))
    values := make([]string, len(cols))
    for i := range pointers {
        pointers[i] = &container[i]
    }

    for rows.Next() {
        if err = rows.Scan(pointers...); err != nil {
            myWriter(nil, err)
            return
        }

        stringLine := strings.Join(values, ",") + "\n"
        myWriter([]byte(stringLine), nil)
    }
}

In the defer section, I would initially, only Close the rows , but then I saw that pg_stat_activity stay open in idle in transaction state, with the FETCH ALL in GRABDATA query.

Calling txn.Exec("CLOSE <cursor_name>") didn't help. After that, I had a CLOSE GRABDATA query in idle in transaction state...

Only when I started calling Commit() did the connection actually close. I thought that maybe I need to call Commit to execute anything on the transation, but if that's the case - how come I got the result of my queries without calling it?

Answer 1

you want to end transaction, not close a declared cursor. commit does it. you can run multiple queries in one transaction - this is why you see the result without committing.

the pg_stat_activity.state values are: active when you run the statement (eg, begin transaction; or fetch cursos ), idle in transaction when you don't currently run statements, but the transaction remains begun and lastly idle , after you run end or commit , so the transaction is over. After you disconnect the session ends and there's no row in pg_stat_activity at all...