go libpq

simulate_cpu_busy.diff

--- testpq.go	2015-07-17 16:18:53.616212373 +0800
+++ testpq2.go	2015-07-17 16:03:03.420162955 +0800
@@ -8,6 +8,9 @@
 	_ "github.com/lib/pq"
 )
 
+//#include <unistd.h>
+import "C"
+
 func query(db *sql.DB, tstart time.Time, tend time.Time) {
 	log.Println("query from", tstart, "to", tend)
 	rows, err := db.Query("select * from users where ts <= $2 and ts > $1", tstart, tend)
@@ -43,8 +46,13 @@
 
 	cur := time.Now().Truncate(time.Minute)
 	tstart, tend := cur.Add(time.Minute*-1), cur
+	start := true
 	for {
 		query(db, tstart, tend)
+		if start {
+			start = false
+			C.sleep(60 * 3)
+		}
 		delta := time.Now().Sub(tend).Minutes()
 		tstart, tend = tend, tend.Add(time.Minute*1)
 		if delta >= 1 {

simulate_cpu_busy.output

2015/07/17 15:45:41 testpq.go:15: query from 2015-07-17 15:44:00 +0800 CST to 2015-07-17 15:45:00 +0800 CST
2015/07/17 15:48:41 testpq.go:15: query from 2015-07-17 15:45:00 +0800 CST to 2015-07-17 15:46:00 +0800 CST
2015/07/17 15:48:41 testpq.go:15: query from 2015-07-17 15:46:00 +0800 CST to 2015-07-17 15:47:00 +0800 CST
2015/07/17 15:48:41 testpq.go:15: query from 2015-07-17 15:47:00 +0800 CST to 2015-07-17 15:48:00 +0800 CST
2015/07/17 15:49:41 testpq.go:15: query from 2015-07-17 15:48:00 +0800 CST to 2015-07-17 15:49:00 +0800 CST

test.go

package main

import (
	"database/sql"
	"log"
	"time"

	_ "github.com/lib/pq"
)

func query(db *sql.DB, tstart time.Time, tend time.Time) {
	log.Println("query from", tstart, "to", tend)
	rows, err := db.Query("select * from users where ts <= $2 and ts > $1", tstart, tend)
	if err != nil {
		log.Fatal(err)
	}
	defer rows.Close()

	var id int
	var name string
	var ts time.Time
	for rows.Next() {
		err := rows.Scan(&id, &name, &ts)
		if err != nil {
			log.Fatal(err)
		}
		log.Println(id, name, ts)
	}
	err = rows.Err()
	if err != nil {
		log.Fatal(err)
	}
}

func main() {
	log.SetFlags(log.LstdFlags | log.Lshortfile)

	db, err := sql.Open("postgres", "postgres://test:test@127.0.0.1:5432/test?sslmode=require")
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	cur := time.Now().Truncate(time.Minute)
	tstart, tend := cur.Add(time.Minute*-1), cur
	for {
		query(db, tstart, tend)
		delta := time.Now().Sub(tend).Minutes()
		tstart, tend = tend, tend.Add(time.Minute*1)
		if delta >= 1 {
			continue
		}
		time.Sleep(time.Minute * 1)
	}
}