Timeouts when calling Set() in concurrent goroutines

[philippgille]

I'm pretty new to Go and very new to Memcached, which is probably a bad combination for using gomemcache, but I couldn't find any info regarding my problem in the docs.

I start Memcached with Docker like this: docker run -it --rm -p 11211:11211 memcached

Then I run this code:

package main

import (
	"fmt"
	"strconv"
	"sync"

	"github.com/bradfitz/gomemcache/memcache"
)

func main() {
	mc := memcache.New("localhost:11211")

	// This one works
	mySet(mc, -1)
	// See:
	myGet(mc, -1)

	goroutineCount := 100
	waitGroup := sync.WaitGroup{}
	waitGroup.Add(goroutineCount)

	for i := 0; i < goroutineCount; i++ {
		go func(i int) {
			// These lead to errors
			mySet(mc, i)
			//waitGroup.Done()
		}(i)
	}
	waitGroup.Wait()
}

func mySet(mc *memcache.Client, i int) {
	item := memcache.Item{
		Key:   strconv.Itoa(i),
		Value: []byte("foo"),
	}
	err := mc.Set(&item)
	if err != nil {
		fmt.Println(err)
	}
}

func myGet(mc *memcache.Client, i int) {
	item, err := mc.Get(strconv.Itoa(i))
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Println("value: " + string(item.Value))
}

waitGroup.Done() is commented out because that leads to more output (?). It's just for reproducing the behavior, so it doesn't matter that the program doesn't finish this way.

This is what I get:

value: foo
read tcp 127.0.0.1:39385->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39379->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39387->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39382->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39389->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39391->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39401->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39394->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39396->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39390->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39409->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39412->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39410->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39413->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39406->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39405->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39415->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39418->127.0.0.1:11211: i/o timeout
read tcp 127.0.0.1:39416->127.0.0.1:11211: i/o timeout
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
read tcp 127.0.0.1:39414->127.0.0.1:11211: i/o timeout
memcache: connect timeout to 127.0.0.1:11211
read tcp 127.0.0.1:39417->127.0.0.1:11211: i/o timeout
memcache: connect timeout to 127.0.0.1:11211
read tcp 127.0.0.1:39425->127.0.0.1:11211: i/o timeout
memcache: connect timeout to 127.0.0.1:11211
read tcp 127.0.0.1:39421->127.0.0.1:11211: i/o timeout
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
read tcp 127.0.0.1:39443->127.0.0.1:11211: i/o timeout
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
memcache: connect timeout to 127.0.0.1:11211
read tcp 127.0.0.1:39419->127.0.0.1:11211: i/o timeout
memcache: connect timeout to 127.0.0.1:11211
read tcp 127.0.0.1:39422->127.0.0.1:11211: i/o timeout

So the first Set() and Get() call work, which indicate that I properly created the client and that the server is running fine. But as soon as the calls take place concurrently in multiple goroutines, I get errors.

The server is still working fine. When I restart the program, the first Set() and Get() still work.

[philippgille]

Okay, I just realized it might actually be the server that can't handle the load properly.

Can anyone confirm this?

[time2k]

Manual increase Client.MaxIdleConns property may help