Use single postgres connection, enable parallel index processing (#77)

src/dipdup/config.py

@@ -76,7 +76,9 @@ class PostgresDatabaseConfig:
 
     @property
     def connection_string(self) -> str:
-        return f'{self.kind}://{self.user}:{self.password}@{self.host}:{self.port}/{self.database}?schema={self.schema_name}'
+        # NOTE: `maxsize=1` is important! Concurrency will be broken otherwise.
+        # NOTE: https://github.com/tortoise/tortoise-orm/issues/792
+        return f'{self.kind}://{self.user}:{self.password}@{self.host}:{self.port}/{self.database}?schema={self.schema_name}&maxsize=1'
 
     @validator('immune_tables')
     def valid_immune_tables(cls, v):

src/dipdup/dipdup.py

@@ -123,10 +123,8 @@ async def run(self, oneshot=False) -> None:
         while True:
             await self.reload_config()
 
-            # FIXME: Process all indexes in parallel, blocked by https://github.com/tortoise/tortoise-orm/issues/792
             async with utils.slowdown(1):
-                for index in self._indexes.values():
-                    await index.process()
+                await asyncio.gather(*[index.process() for index in self._indexes.values()])
 
             # TODO: Continue if new indexes are spawned from origination
             if oneshot: