I have data on my local computer in 2 MySQL databases (dbConnOuter and dbConnInner) that I want to process and collate into a 3rd database (dbConnTarget).
The code runs for about 17000 cycles, then stops with these error messages:
[mysql] 2018/08/06 18:20:57 packets.go:72: unexpected EOF
[mysql] 2018/08/06 18:20:57 packets.go:405: busy buffer
As far as I can tell I'm properly closing the connections where I'm reading from and I'm using Exec for writing, that I believe handles its own resources. I've also tried prepared statements, but it didn't help, the result was the same.
Below is the relevant part of my code, and it does similar database operations prior to this without any issues.
As this is one of my first experiments with Go, I can't yet see where I might be wasting my resources.
import (
"database/sql"
_ "github.com/go-sql-driver/mysql"
)
var dbConnOuter *sql.DB
var dbConnInner *sql.DB
var dbConnTarget *sql.DB
func main() {
dbConnOuter = connectToDb(dbUserDataOne)
dbConnInner = connectToDb(dbUserDataTwo)
dbConnTarget = connectToDb(dbUserDataThree)
// execute various db processing functions
doStuff()
}
func connectToDb(dbUser dbUser) *sql.DB {
dbConn, err := sql.Open("mysql", fmt.Sprintf("%v:%v#tcp(127.0.0.1:3306)/%v", dbUser.username, dbUser.password, dbUser.dbname))
if err != nil {
panic(err)
}
dbConn.SetMaxOpenConns(500)
return dbConn
}
// omitted similar db processing functions that work just fine
func doStuff() {
outerRes, err := dbConnOuter.Query("SELECT some outer data")
if err != nil {
panic(err)
}
defer outerRes.Close()
for outerRes.Next() {
outerRes.Scan(&data1)
innerRes, err := dbConnInner.Query("SELECT some inner data using", data1)
if err != nil {
panic(err)
}
innerRes.Scan(&data2, &data3)
innerRes.Close()
dbConnTarget.Exec("REPLACE INTO whatever", data1, data2, data3)
}
}
Related
So far the hardest part of Go has been understanding how to organize code. It seems incredibly simple on it's face but every time I've tried to do anything I run into circular imports or things like "exported func Start returns unexported type models.dbStore, which can be annoying to use".
Using the following code how do I call db.Close() or am I really not understanding how I'm supposed to provide the database to my models. Here's what I've got:
App.go
package app
import (
"database/sql"
// Comment
_ "github.com/mattn/go-sqlite3"
)
var (
// DB The database connection
db *sql.DB
)
// Setup Sets up the many many app settings
func Setup() {
d, err := sql.Open("sqlite3", "./foo.db")
if err != nil {
panic(err)
}
// TODO: How does the DB get closed?
// defer db.Close()
db = d
}
// GetDB Returns a reference to the database
func GetDB() *sql.DB {
return db
}
Users.go
package models
import (
"github.com/proj/org/app"
)
// User struct
type User struct {
ID int
}
// CreateUser Creates a user
func (u *User) CreateUser() (int64, error) {
// For the sake of brevity just make sure you can
// "connect" to the database
if err := app.GetDB().Ping(); err != nil {
panic(err)
}
return 1234, nil
}
main.go
package main
import (
"fmt"
"net/http"
_ "github.com/mattn/go-sqlite3"
"github.com/proj/org/app"
"github.com/proj/org/models"
)
func homeHandler(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "You are home")
}
func subscribeHandler(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "Subscribing...")
u := models.User{}
u.CreateUser()
}
func main() {
fmt.Println("Running")
app.Setup()
http.HandleFunc("/", homeHandler)
http.HandleFunc("/subscribe", subscribeHandler)
err := http.ListenAndServe(":9090", nil)
if err != nil {
panic(err)
}
}
I thought about doing a app.Shutdown() but that wouldn't work for my most normal use case which is CTRL-C. It would seem if I don't close the database the DB connections would just grow... Just trying to understand.
It's not necessary to close the DB.
The returned DB is safe for concurrent use by multiple goroutines and
maintains its own pool of idle connections. Thus, the Open function
should be called just once. It is rarely necessary to close a DB.
From: https://golang.org/pkg/database/sql/#Open
When your program exits then any open connection is closed, it does not stay open somewhere in the ether awaiting your program to start again, so do not worry about the connections "growing" when you CTRL-C your app.
If, however, you still want to close it, then you can just export a CloseDB function the same way you do with GetDB.
App.go
// ...
func CloseDB() error {
return db.Close()
}
main.go
// ...
func main() {
// ...
app.Setup()
defer app.CloseDB()
// ...
}
I'm facing some issue while fetching the data from the MySQL database using golang below is my code and the error that I'm facing
package main
import (
"database/sql"
"fmt"
_ "github.com/go-sql-driver/mysql"
)
func ConnectMsqlDb() (db *sql.DB, err error) {
db, err = sql.Open("mysql", fmt.Sprintf("%s:%s#tcp(%s:"+sqlDbPort+")/"+sqlDB, sqlUserName, sqlPassword, dbServerIP))
if err != nil {
return nil, err
}
//defer db.Close()
err = db.Ping()
if err != nil {
return nil, err
}
return db, nil
}
func GetSqlData() (err error, data interface{}) {
db, err := ConnectMsqlDb()
if err != nil {
// here it will returning me the error
return err, nil
}
rows, err := db.Query("SELECT * FROM users")
if err != nil {
return err, nil
}
for rows.Next() {
}
defer db.Close()
fmt.Println(rows)
return err, rows
}
func main() {
err, data := GetSqlData()
fmt.Println("data", data, "err", err)
}
error
data commands out of sync. Did you run multiple statements at once?
Can anyone tell me why I'm facing this issue
If the error is comming while opening a connection to mysqld , it could be possible that MySQL server (mysqld) is blocking the host from connecting to it. It means that mysqld has received many connection requests from the given host that were interrupted in the middle.
Read why? To confirm you could see the DB's logs as well. So, a way to unblock it is to flush the cached hosts using the MySQL CLI:
mysql> FLUSH HOSTS;
And then try again to connect.
Plus, give this answer a read as well. Might help.
You can check the state of the socket used by mysqld using (For Linux):
netstat -nt
Check if there's any previously hanging connection from the host to mysqld. If yes, then kill it and try again.
I have a MySQL database with one value in it, a string: "192.168.0.1"
Here is my code:
package main
import (
"database/sql"
"fmt"
_ "github.com/go-sql-driver/mysql"
)
func checkErr(err error) {
if err != nil {
panic(err)
}
}
func main() {
db, err := sql.Open("mysql", "be:me#tcp(127.0.0.1:3306)/ipdb?charset=utf8")
checkErr(err)
ip := "'192.168.0.1'"
rows, err := db.Query("SELECT * FROM Ip_ipdata WHERE ipHost=" + ip)
fmt.Println("insert")
if rows != nil {
for rows.Next() {
var id int
var ip string
err = rows.Scan(&id, &ip)
checkErr(err)
fmt.Println(id)
fmt.Println(ip)
}
} else {
fmt.Println("insert2")
stmt, err2 := db.Prepare("INSERT Ip_ipdata SET ipHost=2")
checkErr(err2)
_, err3 := stmt.Exec(ip)
checkErr(err3)
}
fmt.Println("end")
}
When I put "'192.168.0.1'" in ip it works and shows as expected.
But when I put "'192.168.0.2'" in ip the else statement isn't run and it just exits.
It didn't print "insert2"
screenshot 1
screenshot 2
You should get used to using '?' placeholders in your sql to allow for proper escaping and prevent any potential SQL injection attacks.
You should always check the error in Go before using the returned value.
ip := "192.168.0.1"
rows, err := db.Query("SELECT * FROM Ip_ipdata WHERE ipHost=?", ip)
if err != nil {
// handle error
}
// this will ensure that the DB connection gets put back into the pool
defer rows.Close()
for rows.Next() {
// scan here
}
The Rows returned by Query will not be nil in the case of no results, it will be empty. Try something like this:
func main() {
...
fmt.Println("insert")
checkErr(err)
defer rows.Close()
var found bool
for rows.Next() {
found = true
...
}
if !found {
fmt.Println("insert2")
...
}
fmt.Println("end")
}
Note that like #jmaloney said, more robust error handling is a must as is closing your Rows pointer.
I'm new with golang. I'm trying to share mysql database connection in my package, latter maybe in several packages. To skip defining database connection in every package I've created Database package and now I'm trying to get that package, connect to db and use that object in whole package.
I'm using this mysql plugin: github.com/go-sql-driver/mysql
here is my code:
main.go
package main
import (
"log"
"./packages/db" // this is my custom database package
"database/sql"
_ "github.com/go-sql-driver/mysql"
)
var dbType Database.DatabaseType
var db *sql.DB
func main() {
log.Printf("-- entering main...")
dbType := Database.New()
db = dbType.GetDb()
dbType.DbConnect()
delete_test_data()
dbType.DbClose()
}
func delete_test_data(){
log.Printf("-- entering delete_test_data...")
//db.Exec("DELETE FROM test;")
}
packages/db/db.go
package Database
import (
"log"
"database/sql"
_ "github.com/go-sql-driver/mysql"
)
type DatabaseType struct {
DatabaseObject *sql.DB
}
func New()(d *DatabaseType) {
d = new(DatabaseType)
//db.DatabaseObject = db.DbConnect()
return d
}
func (d *DatabaseType) DbConnect() *DatabaseType{
log.Printf("-- entering DbConnect...")
var err error
if d.DatabaseObject == nil {
log.Printf("--------- > Database IS NIL...")
d.DatabaseObject, err = sql.Open("mysql", "...")
if err != nil {
panic(err.Error())
}
err = d.DatabaseObject.Ping()
if err != nil {
panic(err.Error())
}
}
return d
}
func (d *DatabaseType) DbClose(){
log.Printf("-- entering DbClose...")
defer d.DatabaseObject.Close()
}
func (d *DatabaseType) GetDb() *sql.DB{
return d.DatabaseObject
}
Everything is ok and without error until I uncomment this line:
db.Exec("DELETE FROM test;")
Can someone tell me what is correct way to share db connection?
Your dbType.DbConnect() method returns a DatabaseType with an initialized connection, but you're ignoring the return value entirely.
Further - to simplify your code - look at having New(host string) *DB instead of three different functions (New/DbConnect/GetDb) that do the same thing.
e.g.
package datastore
type DB struct {
// Directly embed this
*sql.DB
}
func NewDB(host string) (*DB, error) {
db, err := sql.Open(...)
if err != nil {
return nil, err
}
return &DB{db}, nil
}
package main
var db *datastore.DB
func main() {
var err error
db, err = datastore.NewDB(host)
if err != nil {
log.Fatal(err)
}
err := someFunc()
}
func someFunc() error {
rows, err := db.Exec("DELETE FROM ...")
// Handle the error, parse the result, etc.
}
This reduces the juggling you have to do, and you can still call close on your DB type because it embeds *sql.DB - there's no need to implement your own Close() method.
So I'm trying to use the OpenID package for Golang, located here: https://github.com/yohcop/openid-go
In the _example it says that it uses in memory storage for storing the nonce/discoverycache information and that it will not free the memory and that I should implement my own version of them using some sort of database.
My database of choice is MySQL, I have tried to implement what I thought was correct (but is not, does not give me any compile errors, but crashes on runtime)
My DiscoveryCache.go is as such:
package openid
import (
"database/sql"
"log"
//"time"
_ "github.com/go-sql-driver/mysql"
"github.com/yohcop/openid-go"
)
type SimpleDiscoveredInfo struct {
opEndpoint, opLocalID, claimedID string
}
func (s *SimpleDiscoveredInfo) OpEndpoint() string { return s.opEndpoint }
func (s *SimpleDiscoveredInfo) OpLocalID() string { return s.opLocalID }
func (s *SimpleDiscoveredInfo) ClaimedID() string { return s.claimedID }
type SimpleDiscoveryCache struct{}
func (s SimpleDiscoveryCache) Put(id string, info openid.DiscoveredInfo) {
/*
db, err := sql.Query("mysql", "db:connectinfo")
errCheck(err)
rows, err := db.Query("SELECT opendpoint, oplocalid, claimedid FROM discovery_cache")
errCheck(err)
was unsure what to do here because I'm not sure how to
return the info properly
*/
log.Println(info)
}
func (s SimpleDiscoveryCache) Get(id string) openid.DiscoveredInfo {
db, err := sql.Query("mysql", "db:connectinfo")
errCheck(err)
var sdi = new(SimpleDiscoveredInfo)
err = db.QueryRow("SELECT opendpoint, oplocalid, claimedid FROM discovery_cache WHERE id=?", id).Scan(&sdi)
errCheck(err)
return sdi
}
And my Noncestore.go
package openid
import (
"database/sql"
"errors"
"flag"
"fmt"
"time"
_ "github.com/go-sql-driver/mysql"
)
var maxNonceAge = flag.Duration("openid-max-nonce-age",
60*time.Second,
"Maximum accepted age for openid nonces. The bigger, the more"+
"memory is needed to store used nonces.")
type SimpleNonceStore struct{}
func (s *SimpleNonceStore) Accept(endpoint, nonce string) error {
db, err := sql.Open("mysql", "dbconnectinfo")
errCheck(err)
if len(nonce) < 20 || len(nonce) > 256 {
return errors.New("Invalid nonce")
}
ts, err := time.Parse(time.RFC3339, nonce[0:20])
errCheck(err)
rows, err := db.Query("SELECT * FROM noncestore")
defer rows.Close()
now := time.Now()
diff := now.Sub(ts)
if diff > *maxNonceAge {
return fmt.Errorf("Nonce too old: %ds", diff.Seconds())
}
d := nonce[20:]
for rows.Next() {
var timeDB, nonce string
err := rows.Scan(&nonce, &timeDB)
errCheck(err)
dbTime, err := time.Parse(time.RFC3339, timeDB)
errCheck(err)
if dbTime == ts && nonce == d {
return errors.New("Nonce is already used")
}
if now.Sub(dbTime) < *maxNonceAge {
_, err := db.Query("INSERT INTO noncestore SET nonce=?, time=?", &nonce, dbTime)
errCheck(err)
}
}
return nil
}
func errCheck(err error) {
if err != nil {
panic("We had an error!" + err.Error())
}
}
Then I try to use them in my main file as:
import _"github.com/mysqlOpenID"
var nonceStore = &openid.SimpleNonceStore{}
var discoveryCache = &openid.SimpleDiscoveryCache{}
I get no compile errors but it crashes
I'm sure you'll look at my code and go what the hell (I'm fairly new and only have a week or so experience with Golang so please feel free to correct anything)
Obviously I have done something wrong, I basically looked at the NonceStore.go and DiscoveryCache.go on the github for OpenId, replicated it, but replaced the map with database insert and select functions
IF anybody can point me in the right direction on how to implement this properly that would be much appreciated, thanks! If you need anymore information please ask.
Ok. First off, I don't believe you that the code compiles.
Let's look at some mistakes, shall we?
db, err := sql.Open("mysql", "dbconnectinfo")
This line opens a database connection. It should only be used once, preferably inside an init() function. For example,
var db *sql.DB
func init() {
var err error
// Now the db variable above is automagically set to the left value (db)
// of sql.Open and the "var err error" above is the right value (err)
db, err = sql.Open("mysql", "root#tcp(127.0.0.1:3306)")
if err != nil {
panic(err)
}
}
Bang. Now you're connected to your MySQL database.
Now what?
Well this (from Get) is gross:
db, err := sql.Query("mysql", "db:connectinfo")
errCheck(err)
var sdi = new(SimpleDiscoveredInfo)
err = db.QueryRow("SELECT opendpoint, oplocalid, claimedid FROM discovery_cache WHERE id=?", id).Scan(&sdi)
errCheck(err)
Instead, it should be this:
// No need for a pointer...
var sdi SimpleDiscoveredInfo
// Because we take the address of 'sdi' right here (inside Scan)
// And that's a useless (and potentially problematic) layer of indirection.
// Notice how I dropped the other "db, err := sql.Query" part? We don't
// need it because we've already declared "db" as you saw in the first
// part of my answer.
err := db.QueryRow("SELECT ...").Scan(&sdi)
if err != nil {
panic(err)
}
// Return the address of sdi, which means we're returning a pointer
// do wherever sdi is inside the heap.
return &sdi
Up next is this:
/*
db, err := sql.Query("mysql", "db:connectinfo")
errCheck(err)
rows, err := db.Query("SELECT opendpoint, oplocalid, claimedid FROM discovery_cache")
errCheck(err)
was unsure what to do here because I'm not sure how to
return the info properly
*/
If you've been paying attention, we can drop the first sql.Query line.
Great, now we just have:
rows, err := db.Query("SELECT ...")
So, why don't you do what you did inside the Accept method and parse the rows using for rows.Next()... ?