add child chunk preview number limit (#12309)

api/configs/feature/__init__.py

         default=4000,
     )
 
+    CHILD_CHUNKS_PREVIEW_NUMBER: PositiveInt = Field(
+        description="Maximum number of child chunks to preview",
+        default=50,
+    )
+
 
 class MultiModalTransferConfig(BaseSettings):
     MULTIMODAL_SEND_FORMAT: Literal["base64", "url"] = Field(

api/core/rag/index_processor/processor/parent_child_index_processor.py

 import uuid
 from typing import Optional
 
+from configs import dify_config
 from core.model_manager import ModelInstance
 from core.rag.cleaner.clean_processor import CleanProcessor
 from core.rag.datasource.retrieval_service import RetrievalService
             child_nodes = self._split_child_nodes(
                 document, rules, process_rule.get("mode"), kwargs.get("embedding_model_instance")
             )
+            if kwargs.get("preview"):
+                if len(child_nodes) > dify_config.CHILD_CHUNKS_PREVIEW_NUMBER:
+                    child_nodes = child_nodes[: dify_config.CHILD_CHUNKS_PREVIEW_NUMBER]
+
             document.children = child_nodes
             doc_id = str(uuid.uuid4())
             hash = helper.generate_text_hash(document.page_content)