SQLAlchemy 1.0 Documentation
Horizontal sharding support.
Defines a rudimental ‘horizontal sharding’ system which allows a Session to distribute queries and persistence operations across multiple databases.
For a usage example, see the Horizontal Sharding example included in the source distribution.
ShardedSession(shard_chooser, id_chooser, query_chooser, shards=None, query_cls=<class 'sqlalchemy.ext.horizontal_shard.ShardedQuery'>, **kwargs)¶
__init__(shard_chooser, id_chooser, query_chooser, shards=None, query_cls=<class 'sqlalchemy.ext.horizontal_shard.ShardedQuery'>, **kwargs)¶
Construct a ShardedSession.
- shard_chooser¶ – A callable which, passed a Mapper, a mapped instance, and possibly a SQL clause, returns a shard ID. This id may be based off of the attributes present within the object, or on some round-robin scheme. If the scheme is based on a selection, it should set whatever state on the instance to mark it in the future as participating in that shard.
- id_chooser¶ – A callable, passed a query and a tuple of identity values, which should return a list of shard ids where the ID might reside. The databases will be queried in the order of this listing.
- query_chooser¶ – For a given Query, returns the list of shard_ids where the query should be issued. Results from all shards returned will be combined together into a single listing.
- shards¶ – A dictionary of string shard names