diff --git a/src/wechat_decrypt_tool/logging_config.py b/src/wechat_decrypt_tool/logging_config.py
index 4635353..35836b6 100644
--- a/src/wechat_decrypt_tool/logging_config.py
+++ b/src/wechat_decrypt_tool/logging_config.py
@@ -3,6 +3,7 @@
 """
 
 import logging
+import os
 import sys
 from datetime import datetime
 from pathlib import Path
@@ -58,6 +59,11 @@ class WeChatLogger:
     
     def setup_logging(self, log_level: str = "INFO"):
         """设置日志配置"""
+        # Allow overriding via env var for easier debugging (e.g. WECHAT_TOOL_LOG_LEVEL=DEBUG)
+        env_level = str(os.environ.get("WECHAT_TOOL_LOG_LEVEL", "") or "").strip()
+        if env_level:
+            log_level = env_level
+
         # 创建日志目录
         now = datetime.now()
         log_dir = Path("output/logs") / str(now.year) / f"{now.month:02d}" / f"{now.day:02d}"
@@ -88,46 +94,47 @@ class WeChatLogger:
         # 文件处理器
         file_handler = logging.FileHandler(self.log_file, encoding='utf-8')
         file_handler.setFormatter(file_formatter)
-        file_handler.setLevel(getattr(logging, log_level.upper()))
+        level = getattr(logging, str(log_level or "INFO").upper(), logging.INFO)
+        file_handler.setLevel(level)
 
         # 控制台处理器
         console_handler = logging.StreamHandler(sys.stdout)
         console_handler.setFormatter(console_formatter)
-        console_handler.setLevel(getattr(logging, log_level.upper()))
+        console_handler.setLevel(level)
         
         # 配置根日志器
-        root_logger.setLevel(getattr(logging, log_level.upper()))
+        root_logger.setLevel(level)
         root_logger.addHandler(file_handler)
         root_logger.addHandler(console_handler)
         
         # 只为uvicorn日志器添加文件处理器，保持其原有的控制台处理器（带颜色）
         uvicorn_logger = logging.getLogger("uvicorn")
         uvicorn_logger.addHandler(file_handler)
-        uvicorn_logger.setLevel(getattr(logging, log_level.upper()))
+        uvicorn_logger.setLevel(level)
 
         # 只为uvicorn.access日志器添加文件处理器
         uvicorn_access_logger = logging.getLogger("uvicorn.access")
         uvicorn_access_logger.addHandler(file_handler)
-        uvicorn_access_logger.setLevel(getattr(logging, log_level.upper()))
+        uvicorn_access_logger.setLevel(level)
 
         # 只为uvicorn.error日志器添加文件处理器
         uvicorn_error_logger = logging.getLogger("uvicorn.error")
         uvicorn_error_logger.addHandler(file_handler)
-        uvicorn_error_logger.setLevel(getattr(logging, log_level.upper()))
+        uvicorn_error_logger.setLevel(level)
 
         # 配置FastAPI日志器
         fastapi_logger = logging.getLogger("fastapi")
         fastapi_logger.handlers = []
         fastapi_logger.addHandler(file_handler)
         fastapi_logger.addHandler(console_handler)
-        fastapi_logger.setLevel(getattr(logging, log_level.upper()))
+        fastapi_logger.setLevel(level)
         
         # 记录初始化信息
         logger = logging.getLogger(__name__)
         logger.info("=" * 60)
         logger.info("微信解密工具日志系统初始化完成")
         logger.info(f"日志文件: {self.log_file}")
-        logger.info(f"日志级别: {log_level}")
+        logger.info(f"日志级别: {logging.getLevelName(level)}")
         logger.info("=" * 60)
         
         return self.log_file
diff --git a/src/wechat_decrypt_tool/routers/chat.py b/src/wechat_decrypt_tool/routers/chat.py
index 4597bf1..9455ad0 100644
--- a/src/wechat_decrypt_tool/routers/chat.py
+++ b/src/wechat_decrypt_tool/routers/chat.py
@@ -213,6 +213,13 @@ async def stream_chat_realtime_events(
     if not db_storage_dir.exists() or not db_storage_dir.is_dir():
         raise HTTPException(status_code=400, detail="db_storage directory not found for this account.")
 
+    logger.info(
+        "[realtime] SSE stream open account=%s interval_ms=%s db_storage=%s",
+        account_dir.name,
+        int(interval_ms),
+        str(db_storage_dir),
+    )
+
     async def gen():
         last_mtime_ns = 0
         last_heartbeat = 0.0
@@ -226,27 +233,40 @@ async def stream_chat_realtime_events(
         }
         yield f"data: {json.dumps(initial, ensure_ascii=False)}\n\n"
 
-        while True:
-            if await request.is_disconnected():
-                break
+        try:
+            while True:
+                if await request.is_disconnected():
+                    break
 
-            mtime_ns = _scan_db_storage_mtime_ns(db_storage_dir)
-            if mtime_ns and mtime_ns != last_mtime_ns:
-                last_mtime_ns = mtime_ns
-                payload = {
-                    "type": "change",
-                    "account": account_dir.name,
-                    "mtimeNs": int(mtime_ns),
-                    "ts": int(time.time() * 1000),
-                }
-                yield f"data: {json.dumps(payload, ensure_ascii=False)}\n\n"
+                # Avoid blocking the event loop on a potentially large directory walk.
+                scan_t0 = time.perf_counter()
+                try:
+                    mtime_ns = await asyncio.to_thread(_scan_db_storage_mtime_ns, db_storage_dir)
+                except Exception:
+                    mtime_ns = 0
+                scan_ms = (time.perf_counter() - scan_t0) * 1000.0
+                if scan_ms > 1000:
+                    logger.warning("[realtime] SSE scan slow account=%s ms=%.1f", account_dir.name, scan_ms)
 
-            now = time.time()
-            if now - last_heartbeat > 15:
-                last_heartbeat = now
-                yield ": ping\n\n"
+                if mtime_ns and mtime_ns != last_mtime_ns:
+                    last_mtime_ns = mtime_ns
+                    payload = {
+                        "type": "change",
+                        "account": account_dir.name,
+                        "mtimeNs": int(mtime_ns),
+                        "ts": int(time.time() * 1000),
+                    }
+                    logger.info("[realtime] SSE change account=%s mtime_ns=%s", account_dir.name, int(mtime_ns))
+                    yield f"data: {json.dumps(payload, ensure_ascii=False)}\n\n"
 
-            await asyncio.sleep(interval_ms / 1000.0)
+                now = time.time()
+                if now - last_heartbeat > 15:
+                    last_heartbeat = now
+                    yield ": ping\n\n"
+
+                await asyncio.sleep(interval_ms / 1000.0)
+        finally:
+            logger.info("[realtime] SSE stream closed account=%s", account_dir.name)
 
     headers = {"Cache-Control": "no-cache", "Connection": "keep-alive", "X-Accel-Buffering": "no"}
     return StreamingResponse(gen(), media_type="text/event-stream", headers=headers)
@@ -337,7 +357,7 @@ def _ensure_session_last_message_table(conn: sqlite3.Connection) -> None:
 
 
 @router.post("/api/chat/realtime/sync", summary="实时消息同步到解密库（按会话增量）")
-async def sync_chat_realtime_messages(
+def sync_chat_realtime_messages(
     request: Request,
     username: str,
     account: Optional[str] = None,
@@ -357,11 +377,23 @@ async def sync_chat_realtime_messages(
         max_scan = 5000
 
     account_dir = _resolve_account_dir(account)
+    trace_id = f"rt-sync-{int(time.time() * 1000)}-{threading.get_ident()}"
+    logger.info(
+        "[%s] realtime sync start account=%s username=%s max_scan=%s",
+        trace_id,
+        account_dir.name,
+        username,
+        int(max_scan),
+    )
 
     # Lock per (account, username) to avoid concurrent writes to the same sqlite tables.
+    logger.info("[%s] acquiring per-session lock account=%s username=%s", trace_id, account_dir.name, username)
     with _realtime_sync_lock(account_dir.name, username):
+        logger.info("[%s] per-session lock acquired account=%s username=%s", trace_id, account_dir.name, username)
         try:
+            logger.info("[%s] ensure wcdb connected account=%s", trace_id, account_dir.name)
             rt_conn = WCDB_REALTIME.ensure_connected(account_dir)
+            logger.info("[%s] wcdb connected account=%s handle=%s", trace_id, account_dir.name, int(rt_conn.handle))
         except WCDBRealtimeError as e:
             raise HTTPException(status_code=400, detail=str(e))
 
@@ -369,6 +401,14 @@ async def sync_chat_realtime_messages(
         if not resolved:
             raise HTTPException(status_code=404, detail="Conversation table not found in decrypted databases.")
         msg_db_path, table_name = resolved
+        logger.info(
+            "[%s] resolved decrypted table account=%s username=%s db=%s table=%s",
+            trace_id,
+            account_dir.name,
+            username,
+            str(msg_db_path),
+            table_name,
+        )
 
         msg_conn = sqlite3.connect(str(msg_db_path))
         msg_conn.row_factory = sqlite3.Row
@@ -457,8 +497,34 @@ async def sync_chat_realtime_messages(
 
             while scanned < int(max_scan):
                 take = min(batch_size, int(max_scan) - scanned)
+                logger.info(
+                    "[%s] wcdb_get_messages account=%s username=%s take=%s offset=%s",
+                    trace_id,
+                    account_dir.name,
+                    username,
+                    int(take),
+                    int(offset),
+                )
+                wcdb_t0 = time.perf_counter()
                 with rt_conn.lock:
                     raw_rows = _wcdb_get_messages(rt_conn.handle, username, limit=take, offset=offset)
+                wcdb_ms = (time.perf_counter() - wcdb_t0) * 1000.0
+                logger.info(
+                    "[%s] wcdb_get_messages done account=%s username=%s rows=%s ms=%.1f",
+                    trace_id,
+                    account_dir.name,
+                    username,
+                    len(raw_rows or []),
+                    wcdb_ms,
+                )
+                if wcdb_ms > 2000:
+                    logger.warning(
+                        "[%s] wcdb_get_messages slow account=%s username=%s ms=%.1f",
+                        trace_id,
+                        account_dir.name,
+                        username,
+                        wcdb_ms,
+                    )
                 if not raw_rows:
                     break
 
@@ -526,9 +592,27 @@ async def sync_chat_realtime_messages(
 
                 # Insert older -> newer to keep sqlite btree locality similar to existing data.
                 values = [tuple(r.get(c) for c in insert_cols) for r in reversed(new_rows)]
+                insert_t0 = time.perf_counter()
                 msg_conn.executemany(insert_sql, values)
                 msg_conn.commit()
+                insert_ms = (time.perf_counter() - insert_t0) * 1000.0
                 inserted = len(new_rows)
+                logger.info(
+                    "[%s] sqlite insert done account=%s username=%s inserted=%s ms=%.1f",
+                    trace_id,
+                    account_dir.name,
+                    username,
+                    int(inserted),
+                    insert_ms,
+                )
+                if insert_ms > 1000:
+                    logger.warning(
+                        "[%s] sqlite insert slow account=%s username=%s ms=%.1f",
+                        trace_id,
+                        account_dir.name,
+                        username,
+                        insert_ms,
+                    )
 
             if ("packed_info_data" in insert_cols) and backfill_rows:
                 update_values = []
@@ -539,12 +623,30 @@ async def sync_chat_realtime_messages(
                     update_values.append((pdata, int(r.get("local_id") or 0)))
                 if update_values:
                     before_changes = msg_conn.total_changes
+                    update_t0 = time.perf_counter()
                     msg_conn.executemany(
                         f"UPDATE {quoted_table} SET packed_info_data = ? WHERE local_id = ? AND (packed_info_data IS NULL OR length(packed_info_data) = 0)",
                         update_values,
                     )
                     msg_conn.commit()
+                    update_ms = (time.perf_counter() - update_t0) * 1000.0
                     backfilled = int(msg_conn.total_changes - before_changes)
+                    logger.info(
+                        "[%s] sqlite backfill done account=%s username=%s rows=%s ms=%.1f",
+                        trace_id,
+                        account_dir.name,
+                        username,
+                        int(backfilled),
+                        update_ms,
+                    )
+                    if update_ms > 1000:
+                        logger.warning(
+                            "[%s] sqlite backfill slow account=%s username=%s ms=%.1f",
+                            trace_id,
+                            account_dir.name,
+                            username,
+                            update_ms,
+                        )
 
             # Update session.db so left sidebar ordering/time can follow new messages.
             newest = new_rows[0] if new_rows else None
@@ -636,6 +738,16 @@ async def sync_chat_realtime_messages(
                 finally:
                     sconn.close()
 
+            logger.info(
+                "[%s] realtime sync done account=%s username=%s scanned=%s inserted=%s backfilled=%s maxLocalIdBefore=%s",
+                trace_id,
+                account_dir.name,
+                username,
+                int(scanned),
+                int(inserted),
+                int(backfilled),
+                int(max_local_id),
+            )
             return {
                 "status": "success",
                 "account": account_dir.name,
@@ -750,8 +862,31 @@ def _sync_chat_realtime_messages_for_table(
 
         while scanned < int(max_scan):
             take = min(batch_size, int(max_scan) - scanned)
+            logger.info(
+                "[realtime] wcdb_get_messages account=%s username=%s take=%s offset=%s",
+                account_dir.name,
+                username,
+                int(take),
+                int(offset),
+            )
+            wcdb_t0 = time.perf_counter()
             with rt_conn.lock:
                 raw_rows = _wcdb_get_messages(rt_conn.handle, username, limit=take, offset=offset)
+            wcdb_ms = (time.perf_counter() - wcdb_t0) * 1000.0
+            logger.info(
+                "[realtime] wcdb_get_messages done account=%s username=%s rows=%s ms=%.1f",
+                account_dir.name,
+                username,
+                len(raw_rows or []),
+                wcdb_ms,
+            )
+            if wcdb_ms > 2000:
+                logger.warning(
+                    "[realtime] wcdb_get_messages slow account=%s username=%s ms=%.1f",
+                    account_dir.name,
+                    username,
+                    wcdb_ms,
+                )
             if not raw_rows:
                 break
 
@@ -816,9 +951,25 @@ def _sync_chat_realtime_messages_for_table(
                         continue
 
             values = [tuple(r.get(c) for c in insert_cols) for r in reversed(new_rows)]
+            insert_t0 = time.perf_counter()
             msg_conn.executemany(insert_sql, values)
             msg_conn.commit()
+            insert_ms = (time.perf_counter() - insert_t0) * 1000.0
             inserted = len(new_rows)
+            logger.info(
+                "[realtime] sqlite insert done account=%s username=%s inserted=%s ms=%.1f",
+                account_dir.name,
+                username,
+                int(inserted),
+                insert_ms,
+            )
+            if insert_ms > 1000:
+                logger.warning(
+                    "[realtime] sqlite insert slow account=%s username=%s ms=%.1f",
+                    account_dir.name,
+                    username,
+                    insert_ms,
+                )
 
         if ("packed_info_data" in insert_cols) and backfill_rows:
             update_values = []
@@ -829,12 +980,28 @@ def _sync_chat_realtime_messages_for_table(
                 update_values.append((pdata, int(r.get("local_id") or 0)))
             if update_values:
                 before_changes = msg_conn.total_changes
+                update_t0 = time.perf_counter()
                 msg_conn.executemany(
                     f"UPDATE {quoted_table} SET packed_info_data = ? WHERE local_id = ? AND (packed_info_data IS NULL OR length(packed_info_data) = 0)",
                     update_values,
                 )
                 msg_conn.commit()
+                update_ms = (time.perf_counter() - update_t0) * 1000.0
                 backfilled = int(msg_conn.total_changes - before_changes)
+                logger.info(
+                    "[realtime] sqlite backfill done account=%s username=%s rows=%s ms=%.1f",
+                    account_dir.name,
+                    username,
+                    int(backfilled),
+                    update_ms,
+                )
+                if update_ms > 1000:
+                    logger.warning(
+                        "[realtime] sqlite backfill slow account=%s username=%s ms=%.1f",
+                        account_dir.name,
+                        username,
+                        update_ms,
+                    )
 
         newest = new_rows[0] if new_rows else None
         preview = ""
@@ -938,7 +1105,7 @@ def _sync_chat_realtime_messages_for_table(
 
 
 @router.post("/api/chat/realtime/sync_all", summary="实时消息同步到解密库（全会话增量）")
-async def sync_chat_realtime_messages_all(
+def sync_chat_realtime_messages_all(
     request: Request,
     account: Optional[str] = None,
     max_scan: int = 200,
@@ -953,6 +1120,16 @@ async def sync_chat_realtime_messages_all(
     说明：这是增量同步，不会每次全表扫描；priority_username 会优先同步并可设置更大的 priority_max_scan。
     """
     account_dir = _resolve_account_dir(account)
+    trace_id = f"rt-syncall-{int(time.time() * 1000)}-{threading.get_ident()}"
+    logger.info(
+        "[%s] realtime sync_all start account=%s max_scan=%s priority=%s include_hidden=%s include_official=%s",
+        trace_id,
+        account_dir.name,
+        int(max_scan),
+        str(priority_username or "").strip(),
+        bool(include_hidden),
+        bool(include_official),
+    )
 
     if max_scan < 20:
         max_scan = 20
@@ -966,15 +1143,29 @@ async def sync_chat_realtime_messages_all(
     priority = str(priority_username or "").strip()
     started = time.time()
 
+    logger.info("[%s] acquiring global sync lock account=%s", trace_id, account_dir.name)
     with _realtime_sync_all_lock(account_dir.name):
+        logger.info("[%s] global sync lock acquired account=%s", trace_id, account_dir.name)
         try:
+            logger.info("[%s] ensure wcdb connected account=%s", trace_id, account_dir.name)
             rt_conn = WCDB_REALTIME.ensure_connected(account_dir)
+            logger.info("[%s] wcdb connected account=%s handle=%s", trace_id, account_dir.name, int(rt_conn.handle))
         except WCDBRealtimeError as e:
             raise HTTPException(status_code=400, detail=str(e))
 
         try:
+            logger.info("[%s] wcdb_get_sessions account=%s", trace_id, account_dir.name)
+            wcdb_t0 = time.perf_counter()
             with rt_conn.lock:
                 raw_sessions = _wcdb_get_sessions(rt_conn.handle)
+            wcdb_ms = (time.perf_counter() - wcdb_t0) * 1000.0
+            logger.info(
+                "[%s] wcdb_get_sessions done account=%s sessions=%s ms=%.1f",
+                trace_id,
+                account_dir.name,
+                len(raw_sessions or []),
+                wcdb_ms,
+            )
         except Exception:
             raw_sessions = []
 
@@ -1018,6 +1209,13 @@ async def sync_chat_realtime_messages_all(
         sessions = _dedupe(sessions)
         sessions.sort(key=lambda x: int(x[0] or 0), reverse=True)
         all_usernames = [u for _, u in sessions if u]
+        logger.info(
+            "[%s] sessions prepared account=%s raw=%s filtered=%s",
+            trace_id,
+            account_dir.name,
+            len(raw_sessions or []),
+            len(all_usernames),
+        )
 
         # Skip sessions whose decrypted session.db already has a newer/equal sort_timestamp.
         decrypted_ts_by_user: dict[str, int] = {}
@@ -1080,10 +1278,25 @@ async def sync_chat_realtime_messages_all(
                 continue
             sync_usernames.append(u)
 
+        logger.info(
+            "[%s] sessions need_sync account=%s need_sync=%s skipped_up_to_date=%s",
+            trace_id,
+            account_dir.name,
+            len(sync_usernames),
+            int(skipped_up_to_date),
+        )
+
         if priority and priority in sync_usernames:
             sync_usernames = [priority] + [u for u in sync_usernames if u != priority]
 
         table_map = _resolve_decrypted_message_tables(account_dir, sync_usernames)
+        logger.info(
+            "[%s] resolved decrypted tables account=%s resolved=%s need_sync=%s",
+            trace_id,
+            account_dir.name,
+            len(table_map),
+            len(sync_usernames),
+        )
 
         scanned_total = 0
         inserted_total = 0
@@ -1116,17 +1329,50 @@ async def sync_chat_realtime_messages_all(
                 inserted_total += ins
                 if ins:
                     updated_sessions += 1
+                    logger.info(
+                        "[%s] synced session account=%s username=%s inserted=%s scanned=%s",
+                        trace_id,
+                        account_dir.name,
+                        uname,
+                        ins,
+                        int(result.get("scanned") or 0),
+                    )
             except HTTPException as e:
                 errors.append(f"{uname}: {str(e.detail or '')}".strip())
+                logger.warning(
+                    "[%s] sync session failed account=%s username=%s err=%s",
+                    trace_id,
+                    account_dir.name,
+                    uname,
+                    str(e.detail or "").strip(),
+                )
                 continue
             except Exception as e:
                 errors.append(f"{uname}: {str(e)}".strip())
+                logger.exception(
+                    "[%s] sync session crashed account=%s username=%s",
+                    trace_id,
+                    account_dir.name,
+                    uname,
+                )
                 continue
 
         elapsed_ms = int((time.time() - started) * 1000)
         if len(errors) > 20:
             errors = errors[:20] + [f"... and {len(errors) - 20} more"]
 
+        logger.info(
+            "[%s] realtime sync_all done account=%s sessions_total=%s need_sync=%s synced=%s updated=%s inserted_total=%s elapsed_ms=%s errors=%s",
+            trace_id,
+            account_dir.name,
+            len(all_usernames),
+            len(sync_usernames),
+            int(synced),
+            int(updated_sessions),
+            int(inserted_total),
+            int(elapsed_ms),
+            len(errors),
+        )
         return {
             "status": "success",
             "account": account_dir.name,
@@ -2134,7 +2380,7 @@ async def list_chat_accounts():
 
 
 @router.get("/api/chat/sessions", summary="获取会话列表（聊天左侧列表）")
-async def list_chat_sessions(
+def list_chat_sessions(
     request: Request,
     account: Optional[str] = None,
     limit: int = 400,
@@ -2157,10 +2403,32 @@ async def list_chat_sessions(
 
     rows: list[Any]
     if source_norm == "realtime":
+        trace_id = f"rt-sessions-{int(time.time() * 1000)}-{threading.get_ident()}"
+        logger.info(
+            "[%s] list_sessions realtime start account=%s limit=%s include_hidden=%s include_official=%s preview=%s",
+            trace_id,
+            account_dir.name,
+            int(limit),
+            bool(include_hidden),
+            bool(include_official),
+            str(preview or ""),
+        )
         try:
+            logger.info("[%s] ensure wcdb connected account=%s", trace_id, account_dir.name)
             conn = WCDB_REALTIME.ensure_connected(account_dir)
+            logger.info("[%s] wcdb connected account=%s handle=%s", trace_id, account_dir.name, int(conn.handle))
+            logger.info("[%s] wcdb_get_sessions account=%s", trace_id, account_dir.name)
+            wcdb_t0 = time.perf_counter()
             with conn.lock:
                 raw = _wcdb_get_sessions(conn.handle)
+            wcdb_ms = (time.perf_counter() - wcdb_t0) * 1000.0
+            logger.info(
+                "[%s] wcdb_get_sessions done account=%s sessions=%s ms=%.1f",
+                trace_id,
+                account_dir.name,
+                len(raw or []),
+                wcdb_ms,
+            )
         except WCDBRealtimeError as e:
             raise HTTPException(status_code=400, detail=str(e))
 
@@ -2193,6 +2461,7 @@ async def list_chat_sessions(
 
         norm.sort(key=lambda r: _ts(r.get("sort_timestamp")), reverse=True)
         rows = norm
+        logger.info("[%s] list_sessions realtime normalized account=%s rows=%s", trace_id, account_dir.name, len(rows))
     else:
         session_db_path = account_dir / "session.db"
         sconn = sqlite3.connect(str(session_db_path))
@@ -2873,7 +3142,7 @@ def _collect_chat_messages(
 
 
 @router.get("/api/chat/messages", summary="获取会话消息列表")
-async def list_chat_messages(
+def list_chat_messages(
     request: Request,
     username: str,
     account: Optional[str] = None,