docs: example and API docs improvements

CHANGELOG.md

@@ -4,6 +4,11 @@
   - Setup (onboarding) now sends correctly retentionDuration if specified  
   - `RetentionRule` used in `Bucket` now contains `ShardGroupDurationSeconds` to specify the shard group duration.
 
+### Documentation
+[#242](https://github.com/influxdata/influxdb-client-go/pull/242) Documentation improvements:
+ - [Custom server API example](https://pkg.go.dev/github.com/influxdata/influxdb-client-go/v2#example-Client-CustomServerAPICall) now shows how to create DBRP mapping
+ - Improved documentation about concurrency  
+
 ## 2.2.3 [2021-04-01]
 ### Bug fixes
 1. [#236](https://github.com/influxdata/influxdb-client-go/pull/236) Setting MaxRetries to zero value disables retry strategy.

README.md

@@ -16,6 +16,7 @@ This repository contains the reference Go client for InfluxDB 2.
     - [Basic Example](#basic-example)
     - [Writes in Detail](#writes)
     - [Queries in Detail](#queries)
+    - [Concurrency](#concurrency)
 - [InfluxDB 1.8 API compatibility](#influxdb-18-api-compatibility)
 - [Contributing](#contributing)
 - [License](#license)
@@ -377,7 +378,93 @@ func main() {
     client.Close()
 }    
 ```
+### Concurrency
+InfluxDB Go Client can be used in a concurrent environment. All its functions are thread safe.
 
+The best practise is to use a single `Client` instance per server URL. This ensures optimized resources usage, 
+most importantly reusing HTTP connections. 
+
+For efficient reuse of HTTP resources among multiple clients, create an HTTP client and use `Options.SetHTTPClient()` for setting it to all clients:
+```go
+    // Create HTTP client
+	httpClient := &http.Client{
+		Timeout: time.Second * time.Duration(60),
+		Transport: &http.Transport{
+			DialContext: (&net.Dialer{
+				Timeout: 5 * time.Second,
+			}).DialContext,
+			TLSHandshakeTimeout: 5 * time.Second,
+			TLSClientConfig: &tls.Config{
+				InsecureSkipVerify: true,
+			},
+			MaxIdleConns:        100,
+			MaxIdleConnsPerHost: 100,
+			IdleConnTimeout:     90 * time.Second,
+		},
+	}
+    // Client for server 1
+    client1 := influxdb2.NewClientWithOptions("https://server:8086", "my-token", influxdb2.DefaultOptions().SetHTTPClient(httpClient))
+    // Client for server 2
+    client2 := influxdb2.NewClientWithOptions("https://server:9999", "my-token2", influxdb2.DefaultOptions().SetHTTPClient(httpClient))
+
+```
+
+Client ensures that there is a single instance of each server API sub-client for the specific area. E.g. a single `WriteAPI` instance for each org/bucket pair, 
+a single `QueryAPI` for each org.
+
+Such a single API sub-client instance can be used concurrently:
+```go
+package main
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+
+	influxdb2 "github.com/influxdata/influxdb-client-go"
+	"github.com/influxdata/influxdb-client-go/v2/api/write"
+)
+
+func main() {
+    // Create client
+	client := influxdb2.NewClient("http://localhost:8086", "my-token")
+    // Ensure closing the client
+    defer client.Close()
+
+	// Get write client
+    writeApi := client.WriteAPI("my-org", "my-bucket")
+
+    // Create channel for points feeding
+	pointsCh := make(chan *write.Point, 200)
+
+	threads := 5
+
+	var wg sync.WaitGroup
+	go func(points int) {
+		for i := 0; i < points; i++ {
+			p := influxdb2.NewPoint("meas",
+				map[string]string{"tag": "tagvalue"},
+				map[string]interface{}{"val1": rand.Int63n(1000), "val2": rand.Float64()*100.0 - 50.0},
+				time.Now())
+			pointsCh <- p
+		}
+		close(pointsCh)
+	}(1000000)
+
+    // Launch write routines
+	for t := 0; t < threads; t++ {
+		wg.Add(1)
+		go func() {
+			for p := range pointsCh {
+				writeApi.WritePoint(p)
+			}
+			wg.Done()
+		}()
+	}
+    // Wait for writes complete
+	wg.Wait()
+}
+```  
 
 ## InfluxDB 1.8 API compatibility
 

api/write.go

@@ -16,6 +16,8 @@ import (
 )
 
 // WriteAPI is Write client interface with non-blocking methods for writing time series data asynchronously in batches into an InfluxDB server.
+// WriteAPI is allowed to be used concurrently.
+// When using multiple goroutines for writing, use a single WriteAPI instance in all goroutines.
 type WriteAPI interface {
 	// WriteRecord writes asynchronously line protocol record into bucket.
 	// WriteRecord adds record into the buffer which is sent on the background when it reaches the batch size.

api/writeAPIBlocking.go

@@ -15,6 +15,10 @@ import (
 
 // WriteAPIBlocking offers blocking methods for writing time series data synchronously into an InfluxDB server.
 // It doesn't implicitly create batches of points. It is intended to use for writing less frequent data, such as a weather sensing, or if there is a need to have explicit control of failed batches.
+//
+// WriteAPIBlocking is allowed to be used concurrently.
+// When using multiple goroutines for writing, use a single WriteAPIBlocking instance in all goroutines.
+//
 // To add implicit batching, use a wrapper, such as:
 //	type writer struct {
 //		batch []*write.Point

client.go

@@ -43,11 +43,14 @@ type Client interface {
 	ServerURL() string
 	// HTTPService returns underlying HTTP service object used by client
 	HTTPService() http.Service
-	// WriteAPI returns the asynchronous, non-blocking, Write client
+	// WriteAPI returns the asynchronous, non-blocking, Write client.
+	// Ensures using a single WriteAPI instance for each org/bucket pair.
 	WriteAPI(org, bucket string) api.WriteAPI
-	// WriteAPIBlocking returns the synchronous, blocking, Write client
+	// WriteAPIBlocking returns the synchronous, blocking, Write client.
+	// Ensures using a single WriteAPIBlocking instance for each org/bucket pair.
 	WriteAPIBlocking(org, bucket string) api.WriteAPIBlocking
-	// QueryAPI returns Query client
+	// QueryAPI returns Query client.
+	// Ensures using a single QueryAPI instance each org.
 	QueryAPI(org string) api.QueryAPI
 	// AuthorizationsAPI returns Authorizations API client.
 	AuthorizationsAPI() api.AuthorizationsAPI

examples_test.go

@@ -31,50 +31,58 @@ func ExampleClient_newClientWithOptions() {
 }
 
 func ExampleClient_customServerAPICall() {
-	// Create a new client using an InfluxDB server base URL and empty token
+	// This example shows how to perform custom server API invocation for any endpoint
+	// Here we will create a DBRP mapping which allows using buckets in legacy write and query (InfluxQL) endpoints
+
+	// Create client. You need an admin token for creating DBRP mapping
 	client := influxdb2.NewClient("http://localhost:8086", "my-token")
+
 	// Always close client at the end
 	defer client.Close()
+
 	// Get generated client for server API calls
 	apiClient := domain.NewClientWithResponses(client.HTTPService())
-	// Get an organization that will own task
-	org, err := client.OrganizationsAPI().FindOrganizationByName(context.Background(), "my-org")
+	ctx := context.Background()
+
+	// Get a bucket we would like to query using InfluxQL
+	b, err := client.BucketsAPI().FindBucketByName(ctx, "my-bucket")
+	if err != nil {
+		panic(err)
+	}
+	// Get an organization that will own the mapping
+	o, err := client.OrganizationsAPI().FindOrganizationByName(ctx, "my-org")
 	if err != nil {
-		//return err
 		panic(err)
 	}
 
-	// Basic task properties
-	taskDescription := "Example task"
-	taskFlux := `option task = {
-  name: "My task",
-  every: 1h
-}
-
-from(bucket:"my-bucket") |> range(start: -1m) |> last()`
-	taskStatus := domain.TaskStatusTypeActive
-
-	// Create TaskCreateRequest object
-	taskRequest := domain.TaskCreateRequest{
-		Org:         &org.Name,
-		OrgID:       org.Id,
-		Description: &taskDescription,
-		Flux:        taskFlux,
-		Status:      &taskStatus,
+	yes := true
+	db := "my-bucket"
+	rp := "autogen"
+	// Fill required fields of the DBRP struct
+	dbrp := domain.DBRP{
+		BucketID:        b.Id,
+		Database:        &db,
+		Default:         &yes,
+		OrgID:           o.Id,
+		RetentionPolicy: &rp,
 	}
 
-	// Issue an API call
-	resp, err := apiClient.PostTasksWithResponse(context.Background(), &domain.PostTasksParams{}, domain.PostTasksJSONRequestBody(taskRequest))
+	params := &domain.PostDBRPParams{}
+	// Call server API
+	resp, err := apiClient.PostDBRPWithResponse(ctx, params, domain.PostDBRPJSONRequestBody(dbrp))
 	if err != nil {
 		panic(err)
 	}
-
-	// Always check generated response errors
+	// Check generated response errors
 	if resp.JSONDefault != nil {
 		panic(resp.JSONDefault.Message)
 	}
+	// Check generated response errors
+	if resp.JSON400 != nil {
+		panic(resp.JSON400.Message)
+	}
 
 	// Use API call result
-	task := resp.JSON201
-	fmt.Println("Created task: ", task.Name)
+	newDbrp := resp.JSON201
+	fmt.Printf("Created DBRP: %#v\n", newDbrp)
 }