diff --git a/block/block_manager.go b/block/block_manager.go
index 167aa5188..66c5537d2 100644
--- a/block/block_manager.go
+++ b/block/block_manager.go
@@ -30,6 +30,9 @@
 	defaultMaxPreambleLength = 32
 	defaultPaddingUnit       = 4096
 	maxInlineContentLength   = 100000 // amount of block data to store in the index block itself
+
+	autoCompactionBlockCount   = 16
+	autoCompactionSafetyMargin = 5 * time.Minute // do not auto-compact if time since block was written is less than this
 )
 
 var zeroTime time.Time
@@ -58,7 +61,6 @@ type Manager struct {
 
 	mu                    sync.Mutex
 	locked                bool
-	indexLoaded           bool
 	blockIDToIndex        map[string]*blockmgrpb.Index
 	packBlockIDToIndex    map[string]*blockmgrpb.Index
 	pendingPackIndexes    []*blockmgrpb.Index
@@ -86,10 +88,6 @@ func (bm *Manager) DeleteBlock(blockID string) error {
 	bm.lock()
 	defer bm.unlock()
 
-	if err := bm.ensurePackIndexesLoaded(); err != nil {
-		return fmt.Errorf("can't load pack index: %v", err)
-	}
-
 	delete(bm.blockIDToIndex, blockID)
 	delete(bm.currentPackIndex.Items, blockID)
 	delete(bm.currentPackIndex.InlineItems, blockID)
@@ -118,10 +116,6 @@ func (bm *Manager) addToIndexLocked(blockID string, ndx *blockmgrpb.Index, packe
 func (bm *Manager) addToPackLocked(blockID string, data []byte, force bool) error {
 	bm.assertLocked()
 
-	if err := bm.ensurePackIndexesLoaded(); err != nil {
-		return fmt.Errorf("can't load pack index: %v", err)
-	}
-
 	if !force {
 		// See if we already have this block ID in the pack.
 		if _, ok := bm.blockIDToIndex[blockID]; ok {
@@ -414,22 +408,26 @@ func (bm *Manager) loadMergedPackIndexLocked() ([]*blockmgrpb.Index, []string, t
 	return merged, blockIDs, blocks[len(blocks)-1].Timestamp, nil
 }
 
-func (bm *Manager) ensurePackIndexesLoaded() error {
-	bm.assertLocked()
+func (bm *Manager) initializeIndexes() error {
+	bm.lock()
+	defer bm.unlock()
 
-	if bm.indexLoaded {
-		return nil
-	}
-
-	merged, _, _, err := bm.loadMergedPackIndexLocked()
+	merged, blockIDs, latestBlockTime, err := bm.loadMergedPackIndexLocked()
 	if err != nil {
 		return err
 	}
+	log.Debug().Msgf("loaded %v index blocks with latest time %v", len(blockIDs), latestBlockTime.Local())
 
-	bm.indexLoaded = true
 	bm.blockIDToIndex, bm.packBlockIDToIndex = dedupeBlockIDsAndIndex(merged)
-	totalBlocks := len(bm.blockIDToIndex)
+	if len(blockIDs) >= autoCompactionBlockCount && latestBlockTime.Before(time.Now().Add(-autoCompactionSafetyMargin)) {
+		log.Debug().Msgf("auto compacting block indexes (block count %v exceeds threshold of %v)", len(blockIDs), autoCompactionBlockCount)
+		merged = removeEmptyIndexes(merged)
+		if _, err := bm.writePackIndexes(merged, &latestBlockTime); err != nil {
+			return err
+		}
+	}
 
+	totalBlocks := len(bm.blockIDToIndex)
 	log.Debug().Int("blocks", totalBlocks).Msgf("loaded indexes")
 
 	return nil
@@ -505,10 +503,6 @@ func (bm *Manager) ListBlocks(prefix string) ([]Info, error) {
 
 	var result []Info
 
-	if err := bm.ensurePackIndexesLoaded(); err != nil {
-		return nil, fmt.Errorf("can't load pack index: %v", err)
-	}
-
 	for b, ndx := range bm.blockIDToIndex {
 		if !strings.HasPrefix(b, prefix) {
 			continue
@@ -592,7 +586,6 @@ func (bm *Manager) IsStorageBlockInUse(storageBlockID string) bool {
 	bm.lock()
 	defer bm.unlock()
 
-	bm.ensurePackIndexesLoaded()
 	return bm.packBlockIDToIndex[storageBlockID] != nil
 }
 
@@ -601,10 +594,6 @@ func (bm *Manager) Repackage(maxLength uint64) error {
 	bm.lock()
 	defer bm.unlock()
 
-	if err := bm.ensurePackIndexesLoaded(); err != nil {
-		return err
-	}
-
 	merged, _, _, err := bm.loadMergedPackIndexLocked()
 	if err != nil {
 		return err
@@ -731,10 +720,6 @@ func (bm *Manager) GetBlock(blockID string) ([]byte, error) {
 	bm.lock()
 	defer bm.unlock()
 
-	if err := bm.ensurePackIndexesLoaded(); err != nil {
-		return nil, fmt.Errorf("can't load pack index: %v", err)
-	}
-
 	if b, err := bm.getPendingBlockLocked(blockID); err == nil {
 		return b, nil
 	}
@@ -747,10 +732,6 @@ func (bm *Manager) BlockInfo(blockID string) (Info, error) {
 	bm.lock()
 	defer bm.unlock()
 
-	if err := bm.ensurePackIndexesLoaded(); err != nil {
-		return Info{}, fmt.Errorf("can't load pack index: %v", err)
-	}
-
 	return bm.blockInfoLocked(blockID)
 }
 
@@ -971,6 +952,10 @@ func newManagerWithTime(st storage.Storage, f FormattingOptions, caching Caching
 
 	m.startPackIndexLocked()
 
+	if err := m.initializeIndexes(); err != nil {
+		return nil, fmt.Errorf("unable initialize indexes: %v", err)
+	}
+
 	return m, nil
 }
 func getCompactedTimestamp(blk string) (time.Time, bool) {