Allow not storing ephemeral node hashes

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## HEAD
 
+* #2568: Allow disabling the writes of ephemeral nodes to storage via the
+  `--tree_ids_with_no_ephemeral_nodes` flag to the sequencer.
+
 ## v1.4.1
 
 * `countFromInformationSchema` function to add support for MySQL 8.

log/sequencer.go

@@ -17,8 +17,10 @@ package log
 import (
 	"bytes"
 	"context"
+	"flag"
 	"fmt"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -64,6 +66,22 @@ var (
 	QuotaIncreaseFactor = 1.1
 )
 
+// The tree IDs for which sequencer does not store ephemeral node hashes.
+// Trillian releases up to v1.4.1 store the ephemeral hashes, which corresponds
+// to this slice being empty. Release v1.4.2 allows disabling this behaviour
+// for individual, or all trees (denoted by the "*" wildcard). The release
+// after v1.4.2 will switch to "*" behaviour unconditionally.
+var idsWithNoEphemeralNodes = make(map[string]bool)
+
+// TODO(pavelkalinnikov): Remove this flag in the next release.
+func init() {
+	var ids string
+	flag.StringVar(&ids, "tree_ids_with_no_ephemeral_nodes", "", "Comma-separated list of tree IDs for which storing the ephemeral nodes is disabled, or * to disable it for all trees")
+	for _, id := range strings.Split(ids, ",") {
+		idsWithNoEphemeralNodes[id] = true
+	}
+}
+
 func quotaIncreaseFactor() float64 {
 	if QuotaIncreaseFactor < 1 {
 		QuotaIncreaseFactor = 1
@@ -185,8 +203,18 @@ func updateCompactRange(cr *compact.Range, leaves []*trillian.LogLeaf, label str
 			return nil, nil, err
 		}
 	}
-	// Store ephemeral nodes on the right border of the tree as well.
-	hash, err := cr.GetRootHash(store)
+
+	// Store or not store ephemeral nodes depending on the flag. This is a
+	// temporary safety measure, to test this on individual trees before fully
+	// disabling ephemeral nodes.
+	storeEphemeral := store
+	if idsWithNoEphemeralNodes[label] || idsWithNoEphemeralNodes["*"] {
+		storeEphemeral = nil
+	}
+
+	// TODO(pavelkalinnikov): Do not store the ephemeral node hashes
+	// unconditionally, because they are not used since v1.4.0.
+	hash, err := cr.GetRootHash(storeEphemeral)
 	if err != nil {
 		return nil, nil, err
 	}

log/sequencer_test.go

@@ -99,10 +99,6 @@ var (
 			ID:   compact.NewNodeID(0, 16),
 			Hash: testonly.MustDecodeBase64("L5Iyd7aFOVewxiRm29xD+EU+jvEo4RfufBijKdflWMk="),
 		},
-		{
-			ID:   compact.NewNodeID(5, 0),
-			Hash: testonly.MustDecodeBase64("R57DrKTGuZdjCNXjv6InGrm4rABLOn9yWpdHmYOoLwU="),
-		},
 	}
 
 	testRoot = &types.LogRootV1{
@@ -128,14 +124,6 @@ var (
 	}
 	// Nodes that will be stored after updating the tree of size 21.
 	updatedNodes21 = []tree.Node{
-		{
-			ID:   compact.NewNodeID(5, 0),
-			Hash: testonly.MustDecodeBase64("1oUtLDlyOWXLHLAvL3NvWaO4D9kr0oQYScylDlgjey4="),
-		},
-		{
-			ID:   compact.NewNodeID(3, 2),
-			Hash: testonly.MustDecodeBase64("1yCvo/9xbNIileBAEjc+c00GxVQQV7h54Tdmkc48uRU="),
-		},
 		{
 			ID:   compact.NewNodeID(1, 10),
 			Hash: testonly.MustDecodeBase64("S55qEsQMx90/eq1fSb87pYCB9WIYL7hBgiTY+B9LmPw="),
@@ -166,6 +154,11 @@ var (
 	})
 )
 
+func init() {
+	// The tree ID used by TestIntegrateBatch.
+	idsWithNoEphemeralNodes["154035"] = true
+}
+
 func makeSLR(root *types.LogRootV1) *trillian.SignedLogRoot {
 	logRoot, _ := root.MarshalBinary()
 	return &trillian.SignedLogRoot{LogRoot: logRoot}