Zap Log Samplers Example

app.go

// Sampled Logs with 10% logging

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

func main() {
	logger, _ := zap.NewProduction()
	sampled := zap.WrapCore(func(c zapcore.Core) zapcore.Core {
		return zapcore.NewSampler(c, time.Second, 10, 100)
	})
	logger = logger.WithOptions(sampled)
	defer logger.Sync()
	logger.Info("Starting the application...")
	// rest of your code
}

app.withrequest_id.go

import (
	"context"
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
	"hash/fnv"
	"math/rand"
)

func main() {
	logger, _ := zap.NewProduction()
	sampled := zap.WrapCore(func(c zapcore.Core) zapcore.Core {
		return zapcore.NewSamplerWithOptions(c, time.Second, 10, 100, func(ctx context.Context) bool {
			v := ctx.Value("requestID")
			if v == nil {
				return rand.Intn(100) < 10
			}
			h := fnv.New64()
			_, _ = h.Write([]byte(v.(string)))
			return h.Sum64()%100 < 10
		})
	})
	logger = logger.WithOptions(sampled)
	defer logger.Sync()
	logger.Info("Starting the application...")

	// Example request logging
	requestID := "123456"
	ctx := context.WithValue(context.Background(), "requestID", requestID)
	logger.Info("Handling request", zap.String("requestID", requestID))
	// rest of your request handling code
}

/* In this example, we're using the zapcore.NewSamplerWithOptions method which takes a custom function 
to determine whether to sample a log entry. The custom function takes the context as a parameter and checks 
if there is a request ID present in the context. If it is present, it hashes the request ID and returns whether
it falls in the 10% range (by checking if the result of h.Sum64() % 100 is less than 10). 
If there is no request ID, it returns the result of a random number generator that returns a value less than 10 with 10% probability. 
This way, logs for the same request will either all be logged or all be dropped. */