Hybrid shadow paging for storing a database

A computer-implemented method for accessing a database state comprising:

• accessing a database having at least two database states stored according to a computer-implemented method for storing a database state including:
• receiving, at the database, one or more write events,
• logging each write event, each logged write event thus forming a new state on the database,
• buffering pages modified or created by the one or more write events, and
• creating a patch by flushing to an append-only database storage the buffered pages when a threshold has been met, the patch comprising a list of new pages that are modified or created by the one or more new write events, the patch representing a state of the database, or a combination of one or more states of the database, and/or part of one or more states of the database;
• receiving, at the database, a read event on an identified state;
• retrieving the patch in a sequence of states from the database storage;
• retrieving a list of logged write events that occurred between the retrieved patch and the identified state;
• and
• applying the list of logged write events to the retrieved patch, thereby recovering the identified state,
• wherein each logged write event has a local mapping table between physical addresses of the buffered pages at the database storage and logical addresses of the pages at a data structure layer of the database, the local mapping table being created by duplicating an existing mapping table in the buffer and applying the local mapping up to a desired logged write event.

A database system comprising:

• a non-transitory computer readable storage medium having recorded thereon a computer program comprising instructions for storing a database state comprising:
• receiving, at a database, one or more write events;
• logging each write event, each logged write event thus forming a new state on the database;
• buffering pages modified or created by the one or more write events;
• and
• creating a patch by flushing to an append-only database storage the buffered pages when a threshold has been met, the patch comprising a list of new pages that are modified or created by the one or more new write events, the patch representing a state of the database, or a combination of one or more states of the database, and/or part of one or more states of the database,
• wherein each logged write event has a local mapping table by duplicating an existing mapping table between physical addresses of the buffered pages at the database storage and logical addresses of the pages at a data structure layer of the database, the local mapping table being created in the buffer and applying the local mapping up to a desired logged write event.

A non-transitory computer-readable medium having recorded thereon a computer program comprising instructions for performing a method for accessing a database state comprising:

• accessing a database having at least two database states stored according to a computer-implemented method for storing a database state including:
• receiving, at the database, one or more write events,
• logging each write event, each logged write event thereby forming a new state on the database,
• buffering pages modified or created by the one or more write events, and
• creating a patch by flushing to an append-only database storage the buffered pages when a threshold has been met, the patch comprising a list of new pages that are modified or created by the one or more new write events, the patch representing a state of the database, or a combination of one or more states of the database, and/or part of one or more states of the database;
• receiving, at the database, a read event on an identified state;
• retrieving a patch in a sequence of states from the database storage;
• retrieving a list of logged write events that occurred between the retrieved patch and the identified state;
• and
• applying the list of logged write events to the retrieved patch, thereby recovering the identified state,
• wherein each logged write event has a local mapping table between physical addresses of the buffered pages at the database storage and logical addresses of the pages at a data structure layer of the database, the local mapping table being created by duplicating an existing mapping table in the buffer and applying the local mapping up to a desired logged write event.