Use AsyncAdaptedQueuePool in aiosqlite

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### Description
Change default pool in `aiosqlite` from `NullPool` to `AsyncAdaptedQueuePool`.
This ensures consistency with pysqlite and least surprise when migrating from sync to async.
See discussion in https://github.com/sqlalchemy/sqlalchemy/discussions/12285
Non regression tested by existing tests.

### Checklist
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This pull request is:

- [ ] A documentation / typographical / small typing error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #12291
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12291
Pull-request-sha: 5a0872b8d431a6937eaf05fb132578aed5723b6a

Change-Id: I96b4d0b5154b34cd26d3ad89774229b0f5d8686f
(cherry picked from commit 11bac714a2e83f6f903b1faf36d744854635da66)

diff --git a/doc/build/changelog/unreleased_20/12285.rst b/doc/build/changelog/unreleased_20/12285.rst
new file mode 100644 (file)
index 0000000..2c1451b
--- /dev/null
+++ b/doc/build/changelog/unreleased_20/12285.rst
@@ -0,0 +1,6 @@
+.. change::
+    :tags: change, sqlite, aiosqlite, asyncio, pool
+    :tickets: 12285
+
+    Changed default connection pool of aiosqlite from NullPool to AsyncAdaptedQueuePool for consistency with pysqlite.
+

diff --git a/lib/sqlalchemy/dialects/sqlite/aiosqlite.py b/lib/sqlalchemy/dialects/sqlite/aiosqlite.py
index c777bf445b0161db1abe50b1bb4f49d1e887b87e..828022454d43f662903bb9137f21302e8c744947 100644 (file)
--- a/lib/sqlalchemy/dialects/sqlite/aiosqlite.py
+++ b/lib/sqlalchemy/dialects/sqlite/aiosqlite.py
@@ -78,6 +78,28 @@ The solution is similar to :ref:`pysqlite_serializable`. This is achieved by the
    with the SQLite driver,
    as this function necessarily will also alter the ".isolation_level" setting.
 
+.. _aiosqlite_pooling:
+
+Pooling Behavior
+----------------
+
+The SQLAlchemy ``aiosqlite`` DBAPI establishes the connection pool differently
+based on the kind of SQLite database that's requested:
+
+* When a ``:memory:`` SQLite database is specified, the dialect by default
+  will use :class:`.StaticPool`. This pool maintains a single
+  connection, so that all access to the engine
+  use the same ``:memory:`` database.
+* When a file-based database is specified, the dialect will use
+  :class:`.AsyncAdaptedQueuePool` as the source of connections.
+
+  .. versionchanged:: 2.0.38
+
+    SQLite file database engines now use :class:`.AsyncAdaptedQueuePool` by default.
+    Previously, :class:`.NullPool` were used.  The :class:`.NullPool` class
+    may be used by specifying it via the
+    :paramref:`_sa.create_engine.poolclass` parameter.
+
 """  # noqa
 
 import asyncio
@@ -380,7 +402,7 @@ class SQLiteDialect_aiosqlite(SQLiteDialect_pysqlite):
     @classmethod
     def get_pool_class(cls, url):
         if cls._is_url_file_db(url):
-            return pool.NullPool
+            return pool.AsyncAdaptedQueuePool
         else:
             return pool.StaticPool