diff --git a/pkg/compactindex/build.go b/pkg/compactindex/build.go
index 5e65a54..42fbcd8 100644
--- a/pkg/compactindex/build.go
+++ b/pkg/compactindex/build.go
@@ -137,7 +137,7 @@ func (b *Builder) sealBucket(ctx context.Context, i int, f *os.File) error {
 	wr := bufio.NewWriter(f)
 	entryBuf := make([]byte, desc.HashLen+intWidth(b.FileSize)) // TODO remove hardcoded constant
 	for _, entry := range entries {
-		desc.storeEntry(entryBuf, entry)
+		desc.marshalEntry(entryBuf, entry)
 		if _, err := wr.Write(entryBuf[:]); err != nil {
 			return fmt.Errorf("failed to write record to index: %w", err)
 		}
diff --git a/pkg/compactindex/build_test.go b/pkg/compactindex/build_test.go
index 7bc0d3b..1f70229 100644
--- a/pkg/compactindex/build_test.go
+++ b/pkg/compactindex/build_test.go
@@ -14,6 +14,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"github.com/vbauerster/mpb/v8/decor"
 )
 
 func TestBuilder(t *testing.T) {
@@ -181,7 +182,7 @@ func TestBuilder_Random(t *testing.T) {
 	const numKeys = uint(500000)
 	const keySize = uint(16)
 	const maxOffset = uint64(1000000)
-	const queries = int(1000)
+	const queries = int(10000)
 
 	// Create new builder session.
 	builder, err := NewBuilder("", numKeys, maxOffset)
@@ -221,7 +222,7 @@ func TestBuilder_Random(t *testing.T) {
 	// Print some stats.
 	targetStat, err := targetFile.Stat()
 	require.NoError(t, err)
-	t.Logf("Index size: %d", targetStat.Size())
+	t.Logf("Index size: %d (% .2f)", targetStat.Size(), decor.SizeB1000(targetStat.Size()))
 	t.Logf("Bytes per entry: %f", float64(targetStat.Size())/float64(numKeys))
 	t.Logf("Indexing speed: %f/s", float64(numKeys)/time.Since(preInsert).Seconds())
 
@@ -237,16 +238,12 @@ func TestBuilder_Random(t *testing.T) {
 		keyN := uint64(rand.Int63n(int64(numKeys)))
 		binary.LittleEndian.PutUint64(key, keyN)
 
-		bucket, err := db.FindBucket(key)
+		bucket, err := db.LookupBucket(key)
 		require.NoError(t, err)
 
-		hash := EntryHash64(bucket.HashDomain, key) & 0xFFFFFF // TODO fix mask
-		entries, err := bucket.Load(1024)
+		value, err := bucket.Lookup(key)
 		require.NoError(t, err)
-
-		// XXX use external binary search here
-		entry := SearchSortedEntries(entries, hash)
-		require.NotNil(t, entry)
+		require.True(t, value > 0)
 	}
 	t.Logf("Queried %d items", queries)
 	t.Logf("Query speed: %f/s", float64(queries)/time.Since(preQuery).Seconds())
diff --git a/pkg/compactindex/compactindex.go b/pkg/compactindex/compactindex.go
index 7d0bbb6..98430dc 100644
--- a/pkg/compactindex/compactindex.go
+++ b/pkg/compactindex/compactindex.go
@@ -183,13 +183,13 @@ type BucketDescriptor struct {
 	OffsetWidth uint8 // with of offset field in bucket
 }
 
-func (b *BucketDescriptor) loadEntry(buf []byte) (e Entry) {
+func (b *BucketDescriptor) unmarshalEntry(buf []byte) (e Entry) {
 	e.Hash = uintLe(buf[0:b.HashLen])
 	e.Value = uintLe(buf[b.HashLen : b.HashLen+b.OffsetWidth])
 	return
 }
 
-func (b *BucketDescriptor) storeEntry(buf []byte, e Entry) {
+func (b *BucketDescriptor) marshalEntry(buf []byte, e Entry) {
 	if len(buf) < int(b.Stride) {
 		panic("serializeEntry: buf too small")
 	}
diff --git a/pkg/compactindex/query.go b/pkg/compactindex/query.go
index a220f75..74f91c9 100644
--- a/pkg/compactindex/query.go
+++ b/pkg/compactindex/query.go
@@ -33,8 +33,19 @@ func Open(stream io.ReaderAt) (*DB, error) {
 	return db, nil
 }
 
-// FindBucket returns a handle to the bucket that might contain the given key.
-func (db *DB) FindBucket(key []byte) (*Bucket, error) {
+// Lookup queries for a key in the index and returns the value (offset), if any.
+//
+// Returns ErrNotFound if the key is unknown.
+func (db *DB) Lookup(key []byte) (uint64, error) {
+	bucket, err := db.LookupBucket(key)
+	if err != nil {
+		return 0, err
+	}
+	return bucket.Lookup(key)
+}
+
+// LookupBucket returns a handle to the bucket that might contain the given key.
+func (db *DB) LookupBucket(key []byte) (*Bucket, error) {
 	return db.GetBucket(db.Header.BucketHash(key))
 }
 
@@ -102,7 +113,7 @@ const targetEntriesPerBucket = 10000
 // Load retrieves all entries in the hashtable.
 func (b *Bucket) Load(batchSize int) ([]Entry, error) {
 	if batchSize <= 0 {
-		batchSize = 1
+		batchSize = 512 // default to reasonable batch size
 	}
 	// TODO bounds check
 	if b.NumEntries > maxEntriesPerBucket {
@@ -119,7 +130,7 @@ func (b *Bucket) Load(batchSize int) ([]Entry, error) {
 		// Decode all entries in it.
 		sub := buf[:n]
 		for len(sub) >= stride {
-			entries = append(entries, b.loadEntry(sub))
+			entries = append(entries, b.unmarshalEntry(sub))
 			sub = sub[stride:]
 			off += int64(stride)
 		}
@@ -134,4 +145,42 @@ func (b *Bucket) Load(batchSize int) ([]Entry, error) {
 	return entries, nil
 }
 
+// TODO: This binary search algo is not optimized for high-latency remotes yet.
+
+// Lookup queries for a key using binary search.
+func (b *Bucket) Lookup(key []byte) (uint64, error) {
+	return b.binarySearch(b.Hash(key))
+}
+
+func (b *Bucket) binarySearch(target uint64) (uint64, error) {
+	low := 0
+	high := int(b.NumEntries)
+	for low <= high {
+		median := (low + high) / 2
+		entry, err := b.loadEntry(median)
+		if err != nil {
+			return 0, err
+		}
+		if entry.Hash == target {
+			return entry.Value, nil
+		} else if entry.Hash < target {
+			low = median + 1
+		} else {
+			high = median - 1
+		}
+	}
+	return 0, ErrNotFound
+}
+
+func (b *Bucket) loadEntry(i int) (Entry, error) {
+	off := int64(i) * int64(b.Stride)
+	buf := make([]byte, b.Stride)
+	n, err := b.Entries.ReadAt(buf, off)
+	if n != len(buf) {
+		return Entry{}, err
+	}
+	return b.unmarshalEntry(buf), nil
+}
+
+// ErrNotFound marks a missing entry.
 var ErrNotFound = errors.New("not found")