diff --git a/env.example b/env.example
index 3529cf58..4b86d79f 100644
--- a/env.example
+++ b/env.example
@@ -74,19 +74,6 @@ ENABLE_LLM_CACHE=true
 ### control the maximum tokens send to LLM (include entities, relations and chunks)
 # MAX_TOTAL_TOKENS=30000
 
-### control the maximum chunk_ids stored in vector and graph db
-# MAX_SOURCE_IDS_PER_ENTITY=300
-# MAX_SOURCE_IDS_PER_RELATION=300
-### control chunk_ids limitation method: KEEP, FIFO (KEPP: Ingore New Chunks, FIFO: New chunks replace old chunks)
-# SOURCE_IDS_LIMIT_METHOD=KEEP
-### Maximum number of file paths stored in entity/relation file_path field
-# MAX_FILE_PATHS=30
-
-### maximum number of related chunks per source entity or relation
-###     The chunk picker uses this value to determine the total number of chunks selected from KG(knowledge graph)
-###     Higher values increase re-ranking time
-# RELATED_CHUNK_NUMBER=5
-
 ### chunk selection strategies
 ###     VECTOR: Pick KG chunks by vector similarity, delivered chunks to the LLM aligning more closely with naive retrieval
 ###     WEIGHT: Pick KG chunks by entity and chunk weight, delivered more solely KG related chunks to the LLM
@@ -148,6 +135,21 @@ SUMMARY_LANGUAGE=English
 ### Maximum context size sent to LLM for description summary
 # SUMMARY_CONTEXT_SIZE=12000
 
+### control the maximum chunk_ids stored in vector and graph db
+# MAX_SOURCE_IDS_PER_ENTITY=300
+# MAX_SOURCE_IDS_PER_RELATION=300
+### control chunk_ids limitation method: FIFO, FIFO
+###    FIFO: First in first out
+###    KEEP: Keep oldest (less merge action and faster)
+# SOURCE_IDS_LIMIT_METHOD=FIFO
+### Maximum number of file paths stored in entity/relation file_path field
+# MAX_FILE_PATHS=30
+
+### maximum number of related chunks per source entity or relation
+###     The chunk picker uses this value to determine the total number of chunks selected from KG(knowledge graph)
+###     Higher values increase re-ranking time
+# RELATED_CHUNK_NUMBER=5
+
 ###############################
 ### Concurrency Configuration
 ###############################
diff --git a/lightrag/constants.py b/lightrag/constants.py
index 7c2b2701..f4e06e11 100644
--- a/lightrag/constants.py
+++ b/lightrag/constants.py
@@ -60,9 +60,12 @@ DEFAULT_RERANK_BINDING = "null"
 # Default source ids limit in meta data for entity and relation
 DEFAULT_MAX_SOURCE_IDS_PER_ENTITY = 300
 DEFAULT_MAX_SOURCE_IDS_PER_RELATION = 300
-SOURCE_IDS_LIMIT_METHOD_KEEP = "KEEP"  # Keep oldest
-SOURCE_IDS_LIMIT_METHOD_FIFO = "FIFO"  # First In First Out (Keep newest)
-DEFAULT_SOURCE_IDS_LIMIT_METHOD = SOURCE_IDS_LIMIT_METHOD_KEEP
+### control chunk_ids limitation method: FIFO, FIFO
+###    FIFO: First in first out
+###    KEEP: Keep oldest (less merge action and faster)
+SOURCE_IDS_LIMIT_METHOD_KEEP = "KEEP"
+SOURCE_IDS_LIMIT_METHOD_FIFO = "FIFO"
+DEFAULT_SOURCE_IDS_LIMIT_METHOD = SOURCE_IDS_LIMIT_METHOD_FIFO
 VALID_SOURCE_IDS_LIMIT_METHODS = {
     SOURCE_IDS_LIMIT_METHOD_KEEP,
     SOURCE_IDS_LIMIT_METHOD_FIFO,