Unmarshal identical dedicatedColumns fields less often (#3952)

* Unmarshal identical dedicatedColumns fields less often

* Clear dedicated column cache at the end of polling

* Update changelog

CHANGELOG.md

@@ -7,7 +7,7 @@
 * [CHANGE] Make vParquet4 the default block encoding [#3810](https://github.com/grafana/tempo/pull/3810) (@ie-pham)
 * [CHANGE] Azure v2 backend becomes the only and primary Azure backend [#3875](https://github.com/grafana/tempo/pull/3875) (@zalegrala)
   **BREAKING CHANGE** The `use_v2_sdk` configuration option has been removed.
-* [CHANGE] BlockMeta improvements to reduce the size [#3950](https://github.com/grafana/tempo/pull/3950) [#3951](https://github.com/grafana/tempo/pull/3951) (@zalegrala)
+* [CHANGE] BlockMeta improvements to reduce the size [#3950](https://github.com/grafana/tempo/pull/3950) [#3951](https://github.com/grafana/tempo/pull/3951) [#3952](https://github.com/grafana/tempo/pull/3952)(@zalegrala)
 * [FEATURE] TraceQL support for link scope and link:traceID and link:spanID [#3741](https://github.com/grafana/tempo/pull/3741) (@stoewer)
 * [FEATURE] TraceQL support for link attribute querying [#3814](https://github.com/grafana/tempo/pull/3814) (@ie-pham)
 * [FEATURE] TraceQL support for event scope and event:name intrinsic [#3708](https://github.com/grafana/tempo/pull/3708) (@stoewer)

tempodb/backend/block_meta.go

@@ -83,9 +83,8 @@ func (s DedicatedColumnScope) ToTempopb() (tempopb.DedicatedColumn_Scope, error)
 }
 
 type CompactedBlockMeta struct {
-	BlockMeta
-
 	CompactedTime time.Time `json:"compactedTime"`
+	BlockMeta
 }
 
 const (
@@ -174,6 +173,25 @@ func (dc *DedicatedColumn) UnmarshalJSON(b []byte) error {
 // DedicatedColumns represents a set of configured dedicated columns.
 type DedicatedColumns []DedicatedColumn
 
+func (dcs *DedicatedColumns) UnmarshalJSON(b []byte) error {
+	// Get the pre-unmarshalled data if available.
+	v := getDedicatedColumns(string(b))
+	if v != nil {
+		*dcs = *v
+		return nil
+	}
+
+	type dcsAlias DedicatedColumns // alias required to avoid recursive calls of UnmarshalJSON
+	err := json.Unmarshal(b, (*dcsAlias)(dcs))
+	if err != nil {
+		return err
+	}
+
+	putDedicatedColumns(string(b), dcs)
+
+	return nil
+}
+
 func NewBlockMeta(tenantID string, blockID uuid.UUID, version string, encoding Encoding, dataEncoding string) *BlockMeta {
 	return NewBlockMetaWithDedicatedColumns(tenantID, blockID, version, encoding, dataEncoding, nil)
 }

tempodb/backend/json.go

@@ -0,0 +1,32 @@
+package backend
+
+import "sync"
+
+var (
+	dedicatedColumnsKeeper = map[string]*DedicatedColumns{}
+	dedicatedColumnsMtx    = sync.Mutex{}
+)
+
+func getDedicatedColumns(b string) *DedicatedColumns {
+	dedicatedColumnsMtx.Lock()
+	defer dedicatedColumnsMtx.Unlock()
+
+	if v, ok := dedicatedColumnsKeeper[b]; ok {
+		return v
+	}
+	return nil
+}
+
+func putDedicatedColumns(b string, d *DedicatedColumns) {
+	dedicatedColumnsMtx.Lock()
+	defer dedicatedColumnsMtx.Unlock()
+
+	dedicatedColumnsKeeper[b] = d
+}
+
+func ClearDedicatedColumns() {
+	dedicatedColumnsMtx.Lock()
+	defer dedicatedColumnsMtx.Unlock()
+
+	clear(dedicatedColumnsKeeper)
+}

tempodb/backend/json_test.go

@@ -0,0 +1,56 @@
+package backend
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func Test_getDedicatedColumns(t *testing.T) {
+	tests := []struct {
+		name     string
+		jsonStr  string
+		expected *DedicatedColumns
+	}{
+		{
+			name:    "case1",
+			jsonStr: `[ {"s": "resource", "n": "namespace"}, {"n": "http.method"}, {"n": "namespace"} ]`,
+			expected: &DedicatedColumns{
+				{Scope: "resource", Name: "namespace", Type: "string"},
+				{Scope: "span", Name: "http.method", Type: "string"},
+				{Scope: "span", Name: "namespace", Type: "string"},
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			// clear the map so we start with a clean slate
+			clear(dedicatedColumnsKeeper)
+
+			v := getDedicatedColumns(tc.jsonStr)
+			require.Nil(t, v)
+
+			dcs := &DedicatedColumns{}
+			err := json.Unmarshal([]byte(tc.jsonStr), dcs)
+			require.NoError(t, err)
+			require.Equal(t, tc.expected, dcs)
+
+			v = getDedicatedColumns(tc.jsonStr)
+			require.Equal(t, dcs, v)
+
+			p1 := fmt.Sprintf("%p", dcs)
+			p2 := fmt.Sprintf("%p", v)
+			require.Equal(t, p1, p2)
+
+			dcs2 := &DedicatedColumns{}
+			err = json.Unmarshal([]byte(tc.jsonStr), dcs2)
+			require.NoError(t, err)
+			require.Equal(t, tc.expected, dcs)
+
+			require.Equal(t, dcs, dcs2)
+		})
+	}
+}

tempodb/blocklist/poller.go

@@ -140,6 +140,7 @@ func (p *Poller) Do(previous *List) (PerTenant, PerTenantCompacted, error) {
 		diff := time.Since(start).Seconds()
 		metricBlocklistPollDuration.Observe(diff)
 		level.Info(p.logger).Log("msg", "blocklist poll complete", "seconds", diff)
+		backend.ClearDedicatedColumns()
 	}()
 
 	ctx, cancel := context.WithCancel(context.Background())