databroker: add options for maximum capacity (#2095)

* databroker: add options

* implement redis

* add trace for enforce options

pkg/storage/inmemory/backend_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/sync/errgroup"
+	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/anypb"
 	"google.golang.org/protobuf/types/known/timestamppb"
 
@@ -150,3 +151,32 @@ func TestStream(t *testing.T) {
 	})
 	require.NoError(t, eg.Wait())
 }
+
+func TestCapacity(t *testing.T) {
+	ctx := context.Background()
+	backend := New()
+	defer func() { _ = backend.Close() }()
+
+	err := backend.SetOptions(ctx, "EXAMPLE", &databroker.Options{
+		Capacity: proto.Uint64(3),
+	})
+	require.NoError(t, err)
+
+	for i := 0; i < 10; i++ {
+		err = backend.Put(ctx, &databroker.Record{
+			Type: "EXAMPLE",
+			Id:   fmt.Sprint(i),
+		})
+		require.NoError(t, err)
+	}
+
+	records, _, err := backend.GetAll(ctx)
+	require.NoError(t, err)
+	assert.Len(t, records, 3)
+
+	var ids []string
+	for _, r := range records {
+		ids = append(ids, r.GetId())
+	}
+	assert.Equal(t, []string{"7", "8", "9"}, ids, "should contain recent records")
+}