Common fault analysis and Countermeasures of using MySQL in go language

Reading guide ： Many students are using it Go In the process of dealing with the database , I often encounter some exceptions and don't know why , This paper starts from SQL The principle of connection pool is analyzed , Some examples are simulated to interpret and analyze abnormal phenomena , And give some common countermeasures , I hope I can help you .

The full text 12795 word , Estimated reading time 32 minute

Many students met MySQL Slow query problems , It may appear as SQL The sentence is very simple , But the query takes a long time . It may be caused by such reasons .

1、 Resources are not released in time

Go Of sql The package uses a long connection to make Client and SQL Server Interaction , for fear of SQL Server Too many links , Usually in Client The terminal limits the maximum number of connections .

Here is sql State diagram of the connection pool （ Set the maximum number of open connections ）：

SQL Client and Server After interaction , Some results return a stream (Stream), Network connection at this time (Conn) Be being Stream Object continues to be used ,Client The results need to be read iteratively , The stream should be closed immediately after reading to reclaim resources ( Release conn).

For example, the longest DB.QueryContext The method is like this ：

// QueryContext  Query some results 
// query：select * from test limit 10
func (db *DB) QueryContext(ctx context.Context, query string, args ...any) (*Rows, error)
type Rows struct{
    Close( ) error 
    ColumnTypes( ) ( [ ]*ColumnType, error) 
    Columns( ) ( [ ]string, error) 
    Err( ) error 
    Next( ) bool 
    NextResultSet( ) bool 
    Scan(dest ...any) error
}

When there are still results ( namely Rows.Next()==true when ), It means that there are still results that have not been read , At this point, you must call Rows.Close() Method to close the stream to release the connection （ Make the current connection idle to Make this connection available to other logic ）.

1.1 experiment 1- Do not call Rows.Close()

If you don't call Close What will happen ？ Let's do an experiment to observe ：

select * from user;
+----+-------+---------------------+----------+--------+
| id | email | register_time       | password | status |
+----+-------+---------------------+----------+--------+
|  2 | dw    | 2011-11-11 11:01:00 | d        |      0 |
+----+-------+---------------------+----------+--------+
1 row in set (0.03 sec)

package main
import (
   "context"
   "database/sql"
   "encoding/json"
   "fmt"
   "sync"
   "time"
   _ "github.com/go-sql-driver/mysql"
)
func main() {
   db, err := sql.Open("mysql", "root:@tcp(127.0.0.1:3306)/test")
   if err != nil {
      panic(err)
   }
   db.SetMaxOpenConns(1)
   //  Start a separate collaboration , For output  DB  Status information 
   go func() {
      tk := time.NewTicker(3 * time.Second)
      defer tk.Stop()
      for range tk.C {
         bf, _ := json.Marshal(db.Stats())
         fmt.Println("db.Stats=", string(bf))
      }
   }()
   //  start-up  10  Collaborators cheng , Query data at the same time 
   var wg sync.WaitGroup
   for i := 0; i < 10; i++ {
      wg.Add(1)
      go func(id int) {
         defer wg.Done()
         queryOne(id, db)
      }(i)
   }
   wg.Wait()
   fmt.Println("finish")
}
func queryOne(id int, db *sql.DB) {
   start := time.Now()
   rows, err := db.QueryContext(context.Background(), "select * from user limit 1")
   if err != nil {
      panic(err)
   }
   // defer rows.Close() 
   //  Not from  Rows  Read the results in , No call  rows.Close
   fmt.Println("id=", id, "hasNext=", rows.Next(), "cost=", time.Since(start))
}

After execution, the following contents will be entered ：

id= 0 hasNext= true cost= 9.607371ms
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}

Read the status data ：

{
    "MaxOpenConnections": 1,  //  Maximum number of open connections , Consistent with the code settings , yes  1
    "OpenConnections": 1,     //  Number of open connections     
    "InUse": 1,               //  Number of connections in use 
    "Idle": 0,                //  Number of idle connections 
    "WaitCount": 9,           //  Number of waiting connections 
    "WaitDuration": 0,        //  The total waiting time （ Count while waiting for exit ）
    "MaxIdleClosed": 0,       //  Exceed the maximum  idle  Count the total number of closed connections  
    "MaxIdleTimeClosed": 0,   //  Overtake and catch up  idle  Total number of connections closed at time 
    "MaxLifetimeClosed": 0    //  The total number of connections closed over the maximum lifetime 
}

As can be seen from the above output , All in all 10 Collaborators cheng , There is only one co process queryOne Method successfully executed , other 9 All processes are in a waiting state .

1.2 experiment 2- call Rows.Close()

If the queryOne Methodical ,“// defer rows.Close()” Remove comments from , That is to say ：

func queryOne(id int, db *sql.DB) {    
    start := time.Now()    
    rows, err := db.QueryContext(context.
Background(), "select * from user limit 1")    
    if err != nil {       
       panic(err)    
    }    
    defer rows.Close() //  Opened the comment here ,Close  Methods release resources     
    fmt.Println("id=", id, "hasNext=", rows.Next(), "cost=", time.Since(start)) 
}

After execution , Will output the following ：

# go run main.go
id= 9 hasNext= true cost= 4.082448ms
id= 3 hasNext= true cost= 5.670052ms
id= 8 hasNext= true cost= 5.745443ms
id= 5 hasNext= true cost= 6.238615ms
id= 6 hasNext= true cost= 6.520818ms
id= 7 hasNext= true cost= 6.697782ms
id= 4 hasNext= true cost= 6.953454ms
id= 1 hasNext= true cost= 7.1079ms
id= 0 hasNext= true cost= 7.3036ms
id= 2 hasNext= true cost= 7.464726ms
finish

The above output results indicate all 10 All the processes have been successfully executed .

1.3 experiment 3- Use the... With timeout Context

Add , Above call QueryContext Method time , It uses context.Background(), So it's the effect of consistent blocking . Actually in use , Incoming context It usually has timeout or supports cancellation , Like this ：

func  queryOne(id int, db *sql.DB) { 
    start := time.Now() 
    ctx,cancel:=context.WithTimeout(context.Background(),time.Second) //  The key      
    defer cancel()  //  The key . If you replace this line with  _=cancel, Another result 
    rows, err := db.QueryContext(ctx , "select * fro m user  limit 1") 
     if err != nil { 
       // panic (err) 
       fmt.Println("BeginTx failed:",err)        
       return 
    } 
    // defer rows.Close () //  Opened the note here   Interpretation of the ,Close   Methods release resources      
    fmt.Println("id=" , id, "hasNext=", rows.Next(), "cost=", time.Since (start)) 
}

After operation, it can be observed that , be-all 10 All the cooperation projects have been successfully implemented ：

id= 9 hasNext= true cost= 1.483715ms
id= 3 hasNext= true cost= 175.675µs
id= 6 hasNext= true cost= 1.277596ms
id= 1 hasNext= true cost= 174.307µs
id= 7 hasNext= true cost= 108.061µs
id= 4 hasNext= true cost= 115.072µs
id= 2 hasNext= true cost= 104.046µs
id= 0 hasNext= true cost= 96.833µs
id= 8 hasNext= true cost= 123.758µs
id= 5 hasNext= true cost= 92.791µs
finish

because context It is with timeout , And when the execution is completed, it will call defer cancel() take ctx Cancel , So even if not used rows.Close Release resources ,ctx In being cancel Resources will also be released immediately after .

If will defer cancel() Replace with _=cancel , Another result  了 , What we're going to see is ：

d= 9 hasNext= true cost= 2.581813ms
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded
BeginTx failed: context deadline exceeded

1.4 Solution

Summary ：

• We should use QueryContext This class supports incoming context Function of , And pass in the... With timeout control context, And after the logic execution is completed , You should use defer Methods will context Cancel .

• For results that return a stream type , After use, you must call Close Method to free resources .

• all *sql.DB、*sql.Tx、*sql.Stmt Return *Conn、*Stmt、*Rows These types all need Close：

type DB/Tx/Stmt struct{
   Conn(ctx context.Context) (*Conn, error)
   Prepare(query string) (*Stmt, error)
   PrepareContext(ctx context.Context, query string) (*Stmt, error)
   Query(query string, args ...any) (*Rows, error)
   QueryContext(ctx context.Context, query string, args ...any) (*Rows, error)
}

To avoid this problem , Generally, you only need to follow the example above , add defer rows.Close() that will do .

If used GDP frame , Read Rows result , have access to mysql.ReadRowsClose Method , After reading , It's automatic Close. such as ：

type user struct {     
   ID           int64     `ddb:"id"`     
   Status       uint8     `ddb:"status"` 
}
func readUsers(ctx context.Context)([]*user,error)
    rows, err := cli.QueryContext(ctx, "select * from user where status=1 limit 5")     
    if err != nil {         
       return nil,err     
    }     
    var userList []*user     
    err=mysql.ReadRowsClose(rows, &userList)     
    return   userList,err
}

Or is it QueryWithBuilderScan：

b := &SimpleBuilder{
  SQL: "SELECT id,name from user where id=1",
 }
 type user struct{
  Name string `ddb:"name"`
  ID int `ddb:"id"`
 }
 var us []*user
 err = mysql.QueryWithBuilderScan(ctx, client, b, &us)

2、 The transaction is incomplete

Open a transaction (Tx) after , Must submit (Commit) Or rollback (Rollback), Otherwise, the transaction will be incomplete , It can also lead to Client End resources ( Connect ) Don't release .

func (db *DB) BeginTx(ctx context.Context, opts *TxOptions) (*Tx, error)
type Tx 
func (tx *Tx) Commit() error    //  Commit transaction 
func (tx *Tx) Rollback ( ) error  //  Roll back the transaction 
func (tx *Tx) Exec(query string, args ...any) (Result, error) 
func (tx *Tx) ExecContext(ctx context.Context, query string, args ...any) (Result, error) 
func (tx *Tx) Prepare(query string) (*Stmt, error) 
func (tx *Tx) PrepareContext(ctx context.Context, query string) (*Stmt, error) 
func (tx *Tx) Query(query string, args ...any) (*Rows, error) 
func (tx *Tx) QueryContext(ctx context.Context, query string, args ...any) (*Rows, error) 
func (tx *Tx) QueryRow(query string, args ...any) *Row 
func (tx *Tx) QueryRowContext(ctx context.Context, query string, args ...any) *Row 
func (tx *Tx) Stmt(stmt *Stmt) *Stmt 
func (tx *Tx) StmtContext(ctx context.Context, stmt *Stmt) *Stmt

2.1 and PHP The difference between

Another thing to note , Use Go Standard library DB.BeginTx Method to start a transaction , You will get a transaction object Tx, Let a batch of SQL Executing in a transaction requires that these SQL Here it is Tx Object . This and PHP It's not the same , For example PHP This is how transactions are used in ：

  <?php
/*  Start a transaction , Turn off auto submit  */
$dbh->beginTransaction(); 
 /*  Insert multiple rows of records based on all or nothing （ Or insert them all , Or not to insert them all ） */
$sql = 'INSERT INTO fruit(name, colour, calories) VALUES (?, ?, ?)';
$sth = $dbh->prepare($sql);
foreach ($fruits as $fruit) {
    $sth->execute(array(
        $fruit->name,
        $fruit->colour,
        $fruit->calories,
    ));
}
/*  Submit changes  */
$dbh->commit();
//  This code comes from  https://www.php.net/manual/zh/pdo.commit.php

While using Go Our business is like this ：

import (
  "context"
  "database/sql"
  "log"
)
var (
  ctx context.Context
  db  *sql.DB
)
func main() {
  tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
  if err != nil {
    log.Fatal(err)
  }
  id := 37
    //  Use  Tx  perform  Update  sentence , Instead of continuing to use  db.Exec
  _, execErr := tx.Exec(`UPDATE users SET status = ? WHERE id = ?`, "paid", id)
  if execErr != nil {
    _ = tx.Rollback()
    log.Fatal(execErr)
  }
  if err := tx.Commit(); err != nil {
    log.Fatal(err)
  }
}
//  This code comes from ：https://pkg.go.dev/database/[email protected]#example-DB.BeginTx

2.2 experiment

Let's continue to experiment with the impact of incomplete transactions , The main part is the same as above ,queryOne The method becomes as follows ：

func queryOne(id int, db *sql.DB) {
   tx,err:=db.BeginTx(context.Background(),nil)
   if err!=nil{
      panic(err)
   }
   // defer tx.Rollback()
   start := time.Now()
   rows, err := tx.QueryContext(context.Background(), "select * from user limit 1")
   if err != nil {
      panic(err)
   }
   defer rows.Close()
   //  The transaction did not roll back 、 Submit 
   fmt.Println("id=", id, "hasNext=", rows.Next(), "cost=", time.Since(start))
}

After execution, the input and the above have no rows.Close similar ：

id= 9 hasNext= true cost= 11.670369ms
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}
db.Stats= {"MaxOpenConnections":1,"OpenConnections":1,"InUse":1,"Idle":0,"WaitCount":9,"WaitDuration":0,"MaxIdleClosed":0,"MaxIdleTimeClosed":0,"MaxLifetimeClosed":0}

Again , All in all 10 Collaborators cheng , There is only one co process queryOne Method successfully executed , other 9 All processes are in a waiting state .

If the above queryOne Methods  // defer tx.Rollback() The comment opens , Then all 10 Each collaboration can be successfully executed .

2.3 Solution

Avoid incomplete transactions , Make sure that the transaction is either Commit, Or be Rollback.

If used GDP frame , have access to mysql.BeginTx Method to use transactions . This scheme can use transactions more safely , Will automatically be based on Function returns a value to determine whether it is Commit still Rollback, If business function appears panic It will also be automatic Rollback.

//  Definition of business logic function , In this function, you can add, delete, change and query in the transaction 
//  return  error==nil  be  tx.Commit(), otherwise  tx.Rollback()
type doFunc func(ctx context.Context, qe QueryExecuto r) error 
func BeginTx(ctx context.Context, cli CanBeginTx, opts *sql.TxOptions, do doFunc) error

var cli mysql.Client
updateUserNameByID := func(ctx context.Context, id uint64, name string) error {
   //   Use  BeginTx  Method , Can handle affairs more easily 
   err := mysql.BeginTx(ctx, cli, nil, func(ctx context.Context, qe mysq.QueryExecutor) error {
      //  Other database update logic is omitted 
      b1 := &mysql.SimpleBuilder{}
      b1.Append("select name from user where uid=?", id)
      var oldName string
      if err := mysql.QueryRowWithBuilderScan(ctx, qe, b1, &oldName); err != nil {
         return err
      }
      if oldName == " Zhugeliang " || oldName == name {
         //  return  err,mysql.BeginTx  Method will rollback the transaction 
         return fmt.Errorf(" No need to update , Overall transaction rollback ")
      }
      b2 := &mysql.SimpleBuilder{}
      b2.Append("update user set name=? where id=?", name, id)
      _, err := mysql.ExecWithBuilder(ctx, qe, b2)
      if err != nil {
         return err
      }
      //  return  nil,mysql.BeginTx  Method will commit the transaction 
      return nil
   })
   return err
}

3、 Other reasons

3.1 Preprocessing is not supported

By default, preprocessing is usually used to promote SQL The security of , Avoid producing SQL Injection problem .

If the cluster version is used in the factory MySQL：DDBS(DRDS), the prepare The support is not good , The performance will be especially poor after use . May behave as , Queries that should have returned in milliseconds , It actually takes hundreds of milliseconds or even seconds to return . In this case, you need to add a configuration item to the parameter interpolateParams=true , close prepare Function .

Name = "demo"
#  Other configuration items are omitted 
[MySQL] 
Username     = "example"
#  Other parameters are omitted 
DSNParams ="charset=utf8&timeout=90s&collation=utf8mb4_unicode_ci&parseTime=true&interpolateParams=true"

4、 How to check

We can use DB Of Stats() Interface to analyze whether the above problems exist . In the above chapters , We just print this data to observe Client Status information .

{    
"MaxOpenConnections" : 1 ,  //  Maximum number of open connections , Consistent with the code settings , yes  1    
"OpenConnections" : 1 ,     //  Number of open connections         
"InUse" : 1 ,               //  Number of connections in use     
"Idle" : 0 ,                //  Number of idle connections     
"WaitCount" : 9 ,           //  Number of waiting connections     
"WaitDuration" : 0 ,        //  The total waiting time （ Count while waiting for exit ）    
"MaxIdleClosed" : 0 ,       //  Exceed the maximum  idle  Count the total number of closed connections      
"MaxIdleTimeClosed" : 0 ,   //  Overtake and catch up  idle  Total number of connections closed at time     
"MaxLifetimeClosed" : 0    //  The total number of connections closed over the maximum lifetime 
}

If you use GDP frame , We can observe this data through the following methods .

4.1 Integrate GDP Application panel

In Baidu factory ,GDP frame （ Inside Baidu   Go Develop Platform, Easy to use 、 Easy to expand 、 Easy to observe 、 Stable and reliable characteristics , Used by thousands of modules ） There's a name "GDP Application panel " Functional module of , This module provides visual UI So that we can easily view 、 Observe various status information of the application . For example, you can view system information 、 File system information 、 Network status information 、 Compile information 、go runtime Information 、 Status information of various components in the framework （ Such as the operation status found by the service 、MySQL、Redis etc. Various Client Connection pool information, etc ）.

Integrating this functionality is very simple , Just add 2 Line configurable code .

After integration , Can pass http://ip:port/debug/panel/?tab=servicer To access this panel , Find the corresponding servicer after （ The address of the page is /debug/panel/?tab=servicer&key={servicer_name} ）, On the page “MySQL ClientStats” The paragraph is the current MySQL Client Of Stats Information . such as ：

---

4.2 Integrated monitoring

GDP The framework's standardized indicator monitoring capability has been applied to all MySQL Client Of Stats Information is collected and output . We can use prometheus perhaps bvar Format output .

After integration , visit http://ip:port/metrics/service You can view the corresponding indicator items , It looks something like this ：

client_connpool{servicer="demo_mysql",stats="ConnType"} 1
client_connpool{servicer="demo_mysql",stats="IPTotal"} 1
client_connpool{servicer="demo_mysql",stats="InUseAvg"} 0
client_connpool{servicer="demo_mysql",stats="InUseMax"} 0
client_connpool{servicer="demo_mysql",stats="InUseTotal"} 0
client_connpool{servicer="demo_mysql",stats="NumOpenAvg"} 0
client_connpool{servicer="demo_mysql",stats="NumOpenCfg"} 100
client_connpool{servicer="demo_mysql",stats="NumOpenMax"} 0
client_connpool{servicer="demo_mysql",stats="NumOpenTotal"} 0

You can add alarms to the above indicators , To help us find and locate problems faster .

4.3 Output to log

If the above 2 Kind of plan , You can also start an asynchronous coroutine , On a regular basis Stats Information output to the log , So that we can analyze the positioning problem .

————————END————————

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