content: emit warning whenever the number of index blobs gets too high, which is an indication that maintenance has not run in a long time

repo/content/content_manager_lock_free.go

@@ -19,6 +19,8 @@
 	"github.com/kopia/kopia/repo/hashing"
 )
 
+const indexBlobCompactionWarningThreshold = 100
+
 // lockFreeManager contains parts of Manager state that can be accessed without locking
 type lockFreeManager struct {
 	// this one is not lock-free
@@ -119,6 +121,10 @@ func (bm *lockFreeManager) loadPackIndexesUnlocked(ctx context.Context) ([]Index
 				return nil, false, err
 			}
 
+			if len(indexBlobs) > indexBlobCompactionWarningThreshold {
+				log(ctx).Warningf("Found too many index blobs (%v), this may result in degraded performance.\n\nPlease ensure periodic repository maintenance is enabled or run 'kopia maintenance'.", len(indexBlobs))
+			}
+
 			return indexBlobs, updated, nil
 		}