diff --git a/src/Storages/MergeTree/MergeTreeSettings.h b/src/Storages/MergeTree/MergeTreeSettings.h
index 713bfffde05..53388617a07 100644
--- a/src/Storages/MergeTree/MergeTreeSettings.h
+++ b/src/Storages/MergeTree/MergeTreeSettings.h
@@ -16,6 +16,10 @@ class ASTStorage;
 struct Settings;
 
 
+/** These settings represent fine tunes for internal details of MergeTree storages
+  * and should not be changed by the user without a reason.
+  */
+
 #define LIST_OF_MERGE_TREE_SETTINGS(M) \
     M(UInt64, min_compress_block_size, 0, "When granule is written, compress the data in buffer if the size of pending uncompressed data is larger or equal than the specified threshold. If this setting is not set, the corresponding global setting is used.", 0) \
     M(UInt64, max_compress_block_size, 0, "Compress the pending uncompressed data in buffer if its size is larger or equal than the specified threshold. Block of data will be compressed even if the current granule is not finished. If this setting is not set, the corresponding global setting is used.", 0) \
@@ -40,7 +44,7 @@ struct Settings;
     M(UInt64, number_of_free_entries_in_pool_to_execute_mutation, 10, "When there is less than specified number of free entries in pool, do not execute part mutations. This is to leave free threads for regular merges and avoid \"Too many parts\"", 0) \
     M(UInt64, max_number_of_merges_with_ttl_in_pool, 2, "When there is more than specified number of merges with TTL entries in pool, do not assign new merge with TTL. This is to leave free threads for regular merges and avoid \"Too many parts\"", 0) \
     M(Seconds, old_parts_lifetime, 8 * 60, "How many seconds to keep obsolete parts.", 0) \
-    M(Seconds, temporary_directories_lifetime, 86400, "How many seconds to keep tmp_-directories.", 0) \
+    M(Seconds, temporary_directories_lifetime, 86400, "How many seconds to keep tmp_-directories. You should not lower this value because merges and mutations may not be able to work with low value of this setting.", 0) \
     M(Seconds, lock_acquire_timeout_for_background_operations, DBMS_DEFAULT_LOCK_ACQUIRE_TIMEOUT_SEC, "For background operations like merges, mutations etc. How many seconds before failing to acquire table locks.", 0) \
     M(UInt64, min_rows_to_fsync_after_merge, 0, "Minimal number of rows to do fsync for part after merge (0 - disabled)", 0) \
     M(UInt64, min_compressed_bytes_to_fsync_after_merge, 0, "Minimal number of compressed bytes to do fsync for part after merge (0 - disabled)", 0) \