Fix concurrency issue when using get_or_create method

CHANGELOG.md

@@ -14,6 +14,7 @@ The format is based on [Keep a Changelog], and this project adheres to [Semantic
 
 - cli: Fixed progress estimation when there are indexes with `last_level` option set.
 - cli: Don't save reports for successful test runs.
+- database: Fixed concurrency issue when using `get_or_create` method.
 - evm: Fixed crash when contract ABI contains overloaded methods.
 - tezos.operations: Fixed `sr_cement` operation index subscription.
 

docs/9.release-notes/_8.0_changelog.md

@@ -29,6 +29,7 @@
 - config: Allow `sentry.dsn` to be empty string.
 - config: Fixed (de)serialization of hex strings in config.
 - config: Fixed setting logging levels according to the config.
+- database: Fixed concurrency issue when using `get_or_create` method.
 - evm.events: Fixed matching logs when filtering by topic0.
 - evm.events: Improve fetching event batches from node.
 - evm.subsquid: Fixed typo in `iter_events` method name.

src/dipdup/config/__init__.py

@@ -157,8 +157,10 @@ def __post_init__(self) -> None:
 
     @property
     def connection_string(self) -> str:
+        # NOTE: `maxsize=1` is important! Concurrency will be broken otherwise.
+        # NOTE: https://github.com/tortoise/tortoise-orm/issues/792
         connection_string = (
-            f'{self.kind}://{self.user}:{quote_plus(self.password)}@{self.host}:{self.port}/{self.database}'
+            f'{self.kind}://{self.user}:{quote_plus(self.password)}@{self.host}:{self.port}/{self.database}?maxsize=1'
         )
         if self.schema_name != DEFAULT_POSTGRES_SCHEMA:
             connection_string += f'&schema={self.schema_name}'