1 files changed, 68 insertions, 0 deletions
diff --git a/internal/git/trace2hooks/log_exporter.go b/internal/git/trace2hooks/log_exporter.go
new file mode 100644
index 000000000..a714d7fb3
--- /dev/null
+++ b/internal/git/trace2hooks/log_exporter.go
@@ -0,0 +1,68 @@
+package trace2hooks
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"gitlab.com/gitlab-org/gitaly/v16/internal/git/trace2"
+	"gitlab.com/gitlab-org/gitaly/v16/internal/log"
+	"golang.org/x/time/rate"
+)
+
+// NewLogExporter initializes LogExporter, which is a hook that uses the parsed
+// trace2 events from the manager to export them to the Gitaly log. It's invocations are limited
+// by the rateLimiter. The limiter allows maxBurstToken number of events to happen at once and then
+// replenishes by maxEventPerSecond. It works on the token bucket algorithm where you have a number
+// of tokens in the bucket to start and you can consume them in each call whilst the bucket gets
+// refilled at the specified rate.
+func NewLogExporter(rl *rate.Limiter, logger log.Logger) *LogExporter {
+	return &LogExporter{
+		rateLimiter: rl,
+		logger:      logger,
+	}
+}
+
+// LogExporter is a trace2 hook that adds trace2 api event logs to Gitaly's logs.
+type LogExporter struct {
+	logger      log.Logger
+	rateLimiter *rate.Limiter
+}
+
+// Name returns the name of tracing exporter
+func (t *LogExporter) Name() string {
+	return "log_exporter"
+}
+
+// Handle will log the trace in a readable json format in Gitaly's logs. Metadata is also collected
+// and additional information is added to the log. It is also rate limited to protect it from overload
+// when there are a lot of trace2 events triggered from git operations.
+func (t *LogExporter) Handle(rootCtx context.Context, trace *trace2.Trace) error {
+	if !t.rateLimiter.Allow() {
+		// When the event is not allowed, return an error to the caller, this may cause traces to be skipped/dropped.
+		return fmt.Errorf("rate has exceeded current limit")
+	}
+
+	trace.Walk(rootCtx, func(ctx context.Context, t *trace2.Trace) context.Context {
+		t.SetMetadata("elapsed_ms", fmt.Sprintf("%d", t.FinishTime.Sub(t.StartTime).Milliseconds()))
+
+		return ctx
+	})
+
+	childrenJSON, err := json.Marshal(trace.Children)
+	if err != nil {
+		return fmt.Errorf("marshal json: %w", err)
+	}
+	escapedChildren := json.RawMessage(childrenJSON)
+
+	t.logger.WithFields(log.Fields{
+		"name":        trace.Name,
+		"thread":      trace.Thread,
+		"component":   "trace2hooks." + t.Name(),
+		"start_time":  trace.StartTime,
+		"finish_time": trace.FinishTime,
+		"metadata":    trace.Metadata,
+		"children":    escapedChildren,
+	}).Info("Git Trace2 API")
+	return nil
+}