I am processing a bunch of files and then dumping the results in PostgreSQL. I would like to process many workers at the same time but keep getting the error "pq: sorry, too many clients already". This seems to happen whenever workers is > 100 or so. (For simplicity, the code below demonstrates the process but instead of processing a file I am simply inserting 1M rows in each table).
Since I am reusing the same *db why am I getting this error? Does each transaction count as a client or am I doing something wrong?
package main
import (
"database/sql"
"flag"
"fmt"
"log"
"sync"
"github.com/lib/pq"
)
func process(db *sql.DB, table string) error {
if _, err := db.Exec(fmt.Sprintf(`DROP TABLE IF EXISTS %v;`, table)); err != nil {
return err
}
col := "age"
s := fmt.Sprintf(`
CREATE TABLE %v (
pk serial PRIMARY KEY,
%v int NOT NULL
)`, table, col)
_, err := db.Exec(s)
if err != nil {
return err
}
tx, err := db.Begin()
if err != nil {
return err
}
defer func() {
if err != nil {
tx.Rollback()
return
}
err = tx.Commit()
}()
stmt, err := tx.Prepare(pq.CopyIn(table, col))
if err != nil {
return err
}
defer func() {
err = stmt.Close()
}()
for i := 0; i < 1e6; i++ {
if _, err = stmt.Exec(i); err != nil {
return err
}
}
return err
}
func main() {
var u string
flag.StringVar(&u, "user", "", "user")
var pass string
flag.StringVar(&pass, "pass", "", "pass")
var host string
flag.StringVar(&host, "host", "", "host")
var database string
flag.StringVar(&database, "database", "", "database")
var workers int
flag.IntVar(&workers, "workers", 10, "workers")
flag.Parse()
db, err := sql.Open("postgres",
fmt.Sprintf(
"user=%s password=%s host=%s database=%s sslmode=require",
u, pass, host, database,
),
)
if err != nil {
log.Fatalln(err)
}
defer db.Close()
db.SetMaxIdleConns(0)
var wg sync.WaitGroup
ch := make(chan int)
for i := 0; i < workers; i++ {
wg.Add(1)
go func() {
defer wg.Done()
for i := range ch {
table := fmt.Sprintf("_table%d", i)
log.Println(table)
if err := process(db, table); err != nil {
log.Fatalln(err)
}
}
}()
}
for i := 0; i < 300; i++ {
ch <- i
}
close(ch)
wg.Wait()
}
I realize I can simply increase the posgresql settings but would like to understand the question: How to increase the max connections in postgres?