Category Archives: Programming

PgBouncer and prepared statements

In our system, we use connection pooler called PgBouncer as a proxy to PostgreSQL server. PgBouncer has two main modes Session pooling mode This mode is less performant (it’s a default mode). When a client connects, a server connection will be assigned to it for the whole duration it stays connected. So it does not …

Golang: testing http and grpc servers

HTTP server is quite easy to test — here is a nice video about it:

Count lines in git repository

git ls-files | xargs wc -l

1	git ls-files \| xargs wc -l

https://stackoverflow.com/questions/4822471/count-number-of-lines-in-a-git-repository

Algorithms to find fastest route through network

This is a great article on that — https://www.redblobgames.com/pathfinding/a-star/introduction.html (in russain). It tells about Dijkstra, Breadth-first, Greedy and A* algorithms. It’s all about optimization of one travel. To optimize your entire network you should try to use Aint Colony algorithm — http://rain.ifmo.ru/cat/data/theory/unsorted/ant-algo-2006/article.pdf (it’s in russian). Another link to this PDF file — aca

How go code is being compiled to assembler code

https://go.godbolt.org/z/31FyJ3 I was interested in comparing line 15 vs line 17 of the following code:

package main

import "fmt"

type kv struct {
	key   []byte
	value []byte
}

type sliceMap []kv

func (sm *sliceMap) Add(k, v []byte) {
	kvs := *sm
	if cap(kvs) > len(kvs) {
		kvs = kvs[:len(kvs)+1]
	} else {
		kvs = append(kvs, kv{})
	}
	kv := &kvs[len(kvs)-1]
	kv.key = append(kv.key[:0], k...)
	kv.value = append(kv.value[:0], v...)
	*sm = kvs
}

func main() {
	sm := sliceMap{}
	sm.Add([]byte("foo"), []byte("bar"))
	fmt.Println(sm)
}

package main

import "fmt"

type kv struct {

key []byte

value []byte

}

type sliceMap []kv

func (sm *sliceMap) Add(k, v []byte) {

kvs := *sm

if cap(kvs) > len(kvs) {

kvs = kvs[:len(kvs)+1]

} else {

kvs = append(kvs, kv{})

}

kv := &kvs[len(kvs)-1]

kv.key = append(kv.key[:0], k...)

kv.value = append(kv.value[:0], v...)

*sm = kvs

}

func main() {

sm := sliceMap{}

sm.Add([]byte("foo"), []byte("bar"))

fmt.Println(sm)

}

E2E tests in go

I tried it via ginkgo and gomega. It has Agouti with WebDriver support out of the box, but I didn’t use it as we have grpc API. That’s the example (table tests):

var _ = Describe("GetRoute", func() {
	var (
		srClient sr.Client
		srErr    error
	)

	JustBeforeEach(func() {
		srClient, srErr = GetClient()
	})

	DescribeTable("positive cases",
		func(fromGeoPointID, toGeoPointID int, expectedUID string, expectedCostGreaterThan float64) {
			Expect(srErr).NotTo(HaveOccurred())
			Expect(srClient).NotTo(BeNil())

			response, err := srClient.GetRoute(context.TODO(), &sr.GetRouteRequest{
				FromGeoPointId: int64(fromGeoPointID),
				ToGeoPointId:   int64(toGeoPointID),
				Quantity:       1,
				Volume:         1,
				Weight:         1,
			})

			Expect(err).To(Succeed())
			Expect(response).NotTo(BeNil())
			Expect(response.RouteCost).NotTo(BeNil())
			Expect(response.RouteCost.RouteUid).To(HaveSuffix(expectedUID))
			Expect(response.RouteCost.GetCost()).To(BeNumerically(">", expectedCostGreaterThan))
		},
		Entry("from(geo=3)->to(geo=2)", 3, 2, "-3-2", float64(10)),
	)

var _ = Describe("GetRoute", func() {

var (

srClient sr.Client

srErr error

)

JustBeforeEach(func() {

srClient, srErr = GetClient()

})

DescribeTable("positive cases",

func(fromGeoPointID, toGeoPointID int, expectedUID string, expectedCostGreaterThan float64) {

Expect(srErr).NotTo(HaveOccurred())

Expect(srClient).NotTo(BeNil())

response, err := srClient.GetRoute(context.TODO(), &sr.GetRouteRequest{

FromGeoPointId: int64(fromGeoPointID),

ToGeoPointId: int64(toGeoPointID),

Quantity: 1,

Volume: 1,

Weight: 1,

})

Expect(err).To(Succeed())

Expect(response).NotTo(BeNil())

Expect(response.RouteCost).NotTo(BeNil())

Expect(response.RouteCost.RouteUid).To(HaveSuffix(expectedUID))

Expect(response.RouteCost.GetCost()).To(BeNumerically(">", expectedCostGreaterThan))

Entry("from(geo=3)->to(geo=2)", 3, 2, "-3-2", float64(10)),

)

ORM for go

https://github.com/Masterminds/squirrel Never used it as we always write SQL queries manually. But looks okay for ORM (well, actually a query-builder).

How to make grpc call from shell

1 https://github.com/grpc/grpc/blob/master/doc/command_line_tool.md

grpc_cli call localhost:7020 ChatAPI.GetChats "external_user:{id:'30594028',type:1}, limit:10, offset:0, order:ORDER_DESC, requested_by_external_user:{id:'30594028',type:1},with_unread_count:true"

1	grpc_cli call localhost:7020 ChatAPI.GetChats "external_user:{id:'30594028',type:1}, limit:10, offset:0, order:ORDER_DESC, requested_by_external_user:{id:'30594028',type:1},with_unread_count:true"

2 https://github.com/fullstorydev/grpcurl

grpcurl -plaintext -emit-defaults -d '{"lozon_id": 15515160432000}' -H 'User-Name: grpcurl' localhost:7020 points/FindPointByLozonID

1	grpcurl -plaintext -emit-defaults -d '{"lozon_id": 15515160432000}' -H 'User-Name: grpcurl' localhost:7020 points/FindPointByLozonID

How to analyze the performance of your go application in production

You should definitely use chi’s middleware for running pprof and stuff in your admin panel. That’s the repo — https://github.com/go-chi/chi That’s the profiler — https://github.com/go-chi/chi/blob/master/middleware/profiler.go CPU profiling After that you can run something like this in shell:

go tool pprof -png ~/Downloads/profile

1	go tool pprof -png ~/Downloads/profile

Or just open it in the browser:

go tool pprof -http=:1234 ~/Downloads/profile

1	go tool pprof -http=:1234 ~/Downloads/profile

If it opens something different then your browser (sublime …

GOPROXY=https://<some_url> go mod download

1	GOPROXY=https://<some_url> go mod download