perf(db): tune SQLite connection pragmas for small VPS

- synchronous=NORMAL: WAL keeps committed data safe against app crashes
  while skipping an fsync per commit.
- temp_store=MEMORY: temp tables and sorts stay in RAM.
- cache_size=-8000: cap page cache at ~8MB.

Tortoise's SqliteClient applies every non-file_path credential as a PRAGMA
on its single connection, so this is the only place that needs changing.

Author: jcbl1

core/database.py

@@ -25,6 +25,17 @@ def get_db_config() -> dict:
                     "journal_mode": "WAL",
                     "busy_timeout": 10000,
                     "foreign_keys": "ON",
+                    # 小内存 VPS 下的 IOPS 与内存折中。Tortoise 的 SqliteClient 会把
+                    # credentials 中 file_path 以外的键逐条执行成 PRAGMA，且 SQLite
+                    # 后端只维持单条连接，因此这些设置在进程生命周期内全局生效。
+                    # synchronous=NORMAL：WAL 下应用崩溃不丢已提交事务，
+                    #   仅 OS/断电可能丢最后若干事务，省去每次提交的 fsync。
+                    # temp_store=MEMORY：临时表与排序走内存，小库收益明显；
+                    #   后台大排序的内存峰值需在压测中关注。
+                    # cache_size=-8000：page cache 上限约 8MB（负数单位为 KiB）。
+                    "synchronous": "NORMAL",
+                    "temp_store": "MEMORY",
+                    "cache_size": -8000,
                 },
             }
         },

tests/test_sqlite_pragmas.py

@@ -0,0 +1,50 @@
+"""SQLite 连接 PRAGMA 生效性验证。
+
+不 mock 配置字典，而是用 get_db_config() 真起一个文件库读取 PRAGMA——
+Tortoise 的 SqliteClient 在 create_connection() 时逐条执行 credentials 中的
+PRAGMA，只有真实连接才能验证这一点。
+"""
+import pytest
+from tortoise import Tortoise
+
+import core.database as database
+from tests.helpers import close_db
+
+
+@pytest.fixture
+async def file_db(tmp_path, monkeypatch):
+    monkeypatch.setattr(database, "_DB_FILE", str(tmp_path / "pragma.db"))
+    if Tortoise._inited:
+        await Tortoise.close_connections()
+    await Tortoise.init(config=database.get_db_config())
+    try:
+        yield Tortoise.get_connection("default")
+    finally:
+        await close_db()
+
+
+async def _pragma(conn, statement: str):
+    rows = await conn.execute_query_dict(statement)
+    return next(iter(rows[0].values()))
+
+
+@pytest.mark.asyncio
+class TestSqlitePragmas:
+    async def test_wal_and_busy_timeout_kept(self, file_db):
+        assert str(await _pragma(file_db, "PRAGMA journal_mode")).lower() == "wal"
+        assert await _pragma(file_db, "PRAGMA busy_timeout") == 10000
+
+    async def test_synchronous_normal(self, file_db):
+        # 1 = NORMAL（WAL 下省 fsync），2 = FULL
+        assert await _pragma(file_db, "PRAGMA synchronous") == 1
+
+    async def test_temp_store_memory(self, file_db):
+        # 0 = DEFAULT，1 = FILE，2 = MEMORY
+        assert await _pragma(file_db, "PRAGMA temp_store") == 2
+
+    async def test_cache_size_8mb(self, file_db):
+        # 负值单位为 KiB
+        assert await _pragma(file_db, "PRAGMA cache_size") == -8000
+
+    async def test_foreign_keys_on(self, file_db):
+        assert await _pragma(file_db, "PRAGMA foreign_keys") == 1