fix: keep the postgres backfill from disabling telemetry or locking the table

src/polygateway/telemetry/postgres.py

@@ -47,8 +47,14 @@ CREATE TABLE IF NOT EXISTS llm_calls (
 
 # 新列排在 created_at 之后: 与旧表 ALTER 追加的位置一致(见 sqlite.py 同款注释)
 _BACKFILL = (
-    "ALTER TABLE llm_calls ADD COLUMN IF NOT EXISTS cached_prompt_tokens INTEGER",
-    "ALTER TABLE llm_calls ADD COLUMN IF NOT EXISTS model_reported TEXT",
+    ("cached_prompt_tokens", "ALTER TABLE llm_calls ADD COLUMN cached_prompt_tokens INTEGER"),
+    ("model_reported", "ALTER TABLE llm_calls ADD COLUMN model_reported TEXT"),
+)
+
+# 探测现有列;尊重 search_path(to_regclass 按当前 search_path 解析)
+_EXISTING_COLUMNS = (
+    "SELECT attname FROM pg_attribute "
+    "WHERE attrelid = to_regclass('llm_calls') AND attnum > 0 AND NOT attisdropped"
 )
 
 _COLUMNS = (
@@ -114,9 +120,7 @@ class PostgresRecorder:
                     self._pool = await asyncpg.create_pool(self._dsn, timeout=10)
                 async with self._pool.acquire() as conn:
                     await conn.execute(_DDL)
-                    for statement in _BACKFILL:
-                        # 已存在的旧表补新列(issue #3);ADD COLUMN IF NOT EXISTS 原生幂等
-                        await conn.execute(statement)
+                    await self._backfill_columns(conn)
                 self._schema_ready = True
                 return self._pool
             except asyncio.CancelledError:
@@ -126,6 +130,29 @@ class PostgresRecorder:
                 logger.warning("Postgres 遥测初始化失败,后续记录降级为 no-op: {}", exc)
                 return None
 
+    async def _backfill_columns(self, conn: object) -> None:
+        """给已存在的旧表补新列(issue #3);**先探测再 ALTER,失败绝不置 `_failed`**。
+
+        两条纪律各有实测理由:
+        ① 不置 `_failed`: 应用账号只有 INSERT 权限时,`ALTER TABLE` 的 ownership
+           检查早于 `IF NOT EXISTS` 的存在性判断——列明明齐全也会失败。置位会让
+           整个 recorder 永久 no-op,与「补列失败只降级为逐行丢弃」的承诺相悖
+           (SQLite 侧同款守卫,两侧必须对称)。
+        ② 先探测: `ADD COLUMN IF NOT EXISTS` 即便列已存在,也会**先取 ACCESS
+           EXCLUSIVE 锁**再判存在性(实测会被一个开着的读事务阻塞)。遥测是内联
+           await,让每个进程的首次写入都去抢共享审计表的排他锁,等于用记录基础设施
+           拖垮业务调用。探测走 ACCESS SHARE,稳态下一条 ALTER 都不会发。
+        """
+        try:
+            existing = {row["attname"] for row in await conn.fetch(_EXISTING_COLUMNS)}  # type: ignore[attr-defined]
+            for column, statement in _BACKFILL:
+                if column not in existing:
+                    await conn.execute(statement)  # type: ignore[attr-defined]
+        except asyncio.CancelledError:
+            raise
+        except Exception as exc:
+            logger.warning("Postgres 遥测补列失败(写入将逐行降级): {}", exc)
+
     async def record_llm_call(self, **fields: object) -> None:
         """写一行遥测;单条失败逐条 warning 丢弃(两级降级之二),绝不冒泡。"""
         pool = await self._ensure_ready()

src/polygateway/telemetry/sqlite.py

@@ -104,15 +104,20 @@ class SQLiteRecorder:
             return
         try:
             existing = {row[1] for row in self._conn.execute("PRAGMA table_info(llm_calls)")}
-            for column, decl in _BACKFILL_COLUMNS:
-                if column in existing:
-                    continue
-                self._conn.execute(f"ALTER TABLE llm_calls ADD COLUMN {column} {decl}")
-            self._conn.commit()
         except sqlite3.Error as exc:
-            # duplicate column: 多进程共库时后到者必然撞上,属预期竞态,视为成功
-            if "duplicate column" not in str(exc).lower():
-                logger.warning("SQLite 遥测补列失败(写入将逐行降级): {}", exc)
+            logger.warning("SQLite 遥测列探测失败(写入将逐行降级): {}", exc)
+            return
+        for column, decl in _BACKFILL_COLUMNS:
+            if column in existing:
+                continue
+            # 逐列独立 try: 一列撞上 duplicate 不得让后面的列漏补
+            try:
+                self._conn.execute(f"ALTER TABLE llm_calls ADD COLUMN {column} {decl}")
+                self._conn.commit()
+            except sqlite3.Error as exc:
+                # duplicate column: 多进程共库时后到者必然撞上,属预期竞态,视为成功
+                if "duplicate column" not in str(exc).lower():
+                    logger.warning("SQLite 遥测补列失败(写入将逐行降级): {}", exc)
 
     async def record_llm_call(self, **fields: object) -> None:
         """写一行遥测;字段集合即 20 字段冻结签名(ports.TelemetryRecorder)。"""