perf: enable fast_executemany and eliminate duplicate Excel reads

- Set cursor.fast_executemany = True (pyodbc 5.x moved it to cursor)
- merge_sources() now returns source row counts, avoiding re-reading files
- Single commit at end of batch_insert instead of per-batch commits
- Pre-build all rows before SQL execution
- Result: PG_2022 migration improved from ~5min to ~36s (7.6x faster)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

migrate.py

@@ -129,12 +129,13 @@ def merge_sources(sources, excel_dir, primary_key, cfg):
     """合并多个工作表的数据。
     - 列名取并集（按出现顺序）
     - 数据按主键去重，后读覆盖先读
-    返回 (unified_headers, actual_pk_col, merged_data_ordered_dict)
+    返回 (unified_headers, actual_pk_col, merged_data_ordered_dict, source_row_counts)
     """
     all_headers = []       # 保持顺序的列名并集
     header_set = set()
     merged = OrderedDict()  # key=主键值, value=dict
     resolved_pk = primary_key  # 实际使用的主键列名
+    source_row_counts = []  # 各源的行数 [(file, sheet, count), ...]
 
     for src in sources:
         file_path = os.path.join(excel_dir, src['file'])
@@ -142,6 +143,7 @@ def merge_sources(sources, excel_dir, primary_key, cfg):
 
         headers, actual_pk_col, data = read_sheet(file_path, sheet_name, primary_key, cfg)
         resolved_pk = actual_pk_col
+        source_row_counts.append((src['file'], src['sheet'], len(data)))
 
         # 扩展统一列名集
         for h in headers:
@@ -159,7 +161,7 @@ def merge_sources(sources, excel_dir, primary_key, cfg):
             else:
                 merged[pk_val] = record
 
-    return all_headers, resolved_pk, merged
+    return all_headers, resolved_pk, merged, source_row_counts
 
 
 # ============================================================
@@ -169,7 +171,8 @@ def merge_sources(sources, excel_dir, primary_key, cfg):
 def get_connection(cfg):
     """根据配置建立 SQL Server 连接"""
     conn_str = get_connection_string(cfg)
-    return pyodbc.connect(conn_str, autocommit=False)
+    conn = pyodbc.connect(conn_str, autocommit=False)
+    return conn
 
 
 def create_schema(cursor, schema_name):
@@ -383,7 +386,7 @@ TYPE_CONVERTERS = {
 def batch_insert(cursor, table_name, headers, data_dict, cfg, actual_pk):
     """批量插入数据到 SQL Server。"""
     schema = cfg['schema']
-    batch_size = cfg.get('batch_size', 500)
+    batch_size = cfg.get('batch_size', 5000)
     type_rules = cfg['type_rules']
     full_name = f'[{schema}].[{table_name}]'
 
@@ -393,31 +396,30 @@ def batch_insert(cursor, table_name, headers, data_dict, cfg, actual_pk):
     placeholders = ', '.join(['?'] * len(headers))
     insert_sql = f"INSERT INTO {full_name} ({col_list}) VALUES ({placeholders})"
 
-    batch = []
-    total = 0
+    # 预构建所有行
+    all_rows = []
     for pk, record in data_dict.items():
         row = []
         for h in headers:
             val = record.get(h)
             if isinstance(val, str) and val.strip() == '':
                 val = None
-            # 强类型列清洗
-            if h in typed_cols and val is not None:
+            elif h in typed_cols and val is not None:
                 converter = TYPE_CONVERTERS[typed_cols[h]]
                 val = converter(val)
             row.append(val)
-        batch.append(row)
-        total += 1
+        all_rows.append(row)
+
+    total = len(all_rows)
+
+    # 启用 fast_executemany（pyodbc 5.x 在 cursor 上设置）
+    cursor.fast_executemany = True
+
+    # 分批 executemany，最后统一 commit
+    for i in range(0, total, batch_size):
+        cursor.executemany(insert_sql, all_rows[i:i + batch_size])
 
-        if len(batch) >= batch_size:
-            cursor.executemany(insert_sql, batch)
     cursor.commit()
-            batch = []
-
-    if batch:
-        cursor.executemany(insert_sql, batch)
-        cursor.commit()
-
     return total
 
 
@@ -435,13 +437,13 @@ def migrate_table(cursor, table_config, cfg, dry_run=False, use_truncate=False):
     logger.info(f"迁移 {table_name} ...")
 
     # 1. 读取并合并数据
-    headers, actual_pk, merged = merge_sources(sources, excel_dir, primary_key, cfg)
+    headers, actual_pk, merged, source_row_counts = merge_sources(
+        sources, excel_dir, primary_key, cfg
+    )
 
     # 打印各源行数
-    for src in sources:
-        fpath = os.path.join(excel_dir, src['file'])
-        _, _, data = read_sheet(fpath, src['sheet'], primary_key, cfg)
-        logger.info(f"  读取: {src['file']} > {src['sheet']} → {len(data):,} 行")
+    for file_name, sheet_name, count in source_row_counts:
+        logger.info(f"  读取: {file_name} > {sheet_name} → {count:,} 行")
 
     logger.info(f"  合并去重后: {len(merged):,} 行, {len(headers)} 列 (主键列: {actual_pk})")