Bulk insert with Golang and Gorm deadlock in concurrency goroutines - mysql

Question

I'm trying to bulk insert many records using Gorm, Golang and MySQL. My code looks like this:
package main
import (
"fmt"
"sync"
"gorm.io/driver/mysql"
"gorm.io/gorm"
)
type Article struct {
gorm.Model
Code string `gorm:"size:255;uniqueIndex"`
}
func main() {
db, err := gorm.Open(mysql.Open("root#tcp(127.0.0.1:3306)/q_test"), nil)
if err != nil {
panic(err)
}
db.AutoMigrate(&Article{})
// err = db.Exec("TRUNCATE articles").Error
err = db.Exec("DELETE FROM articles").Error
if err != nil {
panic(err)
}
// Build some articles
n := 10000
var articles []Article
for i := 0; i < n; i++ {
article := Article{Code: fmt.Sprintf("code_%d", i)}
articles = append(articles, article)
}
// // Save articles
// err = db.Create(&articles).Error
// if err != nil {
// panic(err)
// }
// Save articles with goroutines
chunkSize := 100
var wg sync.WaitGroup
wg.Add(n / chunkSize)
for i := 0; i < n; i += chunkSize {
go func(i int) {
defer wg.Done()
chunk := articles[i:(i + chunkSize)]
err := db.Create(&chunk).Error
if err != nil {
panic(err)
}
}(i)
}
wg.Wait()
}
When I run this code sometimes (about one in three times) I get this error:
panic: Error 1213: Deadlock found when trying to get lock; try restarting transaction
If I run the code without goroutines (commented lines), I get no deadlock. Also, I've noticed that if I remove the unique index on the code field the deadlock doesn't happen anymore. And if I replace the DELETE FROM articles statement with TRUNCATE articles the deadlock doesn't seem to happen anymore.
I've also run the same code with Postgresql and it works, with no deadlocks.
Any idea why the deadlock happens only with the unique index on MySQL and how to avoid it?

Answer 1

DELETE statement is executed using a row lock, each row in the table is locked for deletion.
TRUNCATE TABLE always locks the table and page but not each row.
source : https://stackoverflow.com/a/20559931/18012302
I think mysql need time to do DELETE query.
try add time.Sleep after query delete.
err = db.Exec("DELETE FROM articles").Error
if err != nil {
panic(err)
}
time.Sleep(time.Second)