US 8,527,462 B1Granted

Database point-in-time restore and as-of query

AssigneeMicrosoft Corporation

InventorsTomas Talius, Robin Dhananjay Dhamankar, Hanumantha R. Kodavalla

Life of this patent

Estimating the term…

Loading patent…

Abstract

A database is queried as of any wall-clock time within a retention period, via undo that uses database snapshots and a list of page level modifications. The snapshot is user-identified, automatically generated, or extracted from a backup. The list is maintained in a transaction log by persisting page content before a page is re-used, persisting deleted rows before they are moved, persisting compensation log record undo information, and/or logging a full page. To rewind an entire database, the undo scans the transaction log in reverse LSN order and undoes all page modifications. Undo reverses reallocated pages, table truncation, and/or table deletion, as well as page-level modifications of a schema, metadata values, and/or system tables. An as-of query is handled using as-of page(s) from a sparse page file. If the sparse page file does not already contain the responsive page(s), they are created and added to it.

Claims20

Dependent claims

A computer-readable storage medium configured with data and with instructions that when executed by at least one processor causes the processor(s) to perform a process for accessing a version of database content as it existed at a previous point in time (the “as-of time”), the process comprising the steps of:

acquiring a database snapshot based on a database;
undoing modifications of database content which were made after the as-of time, said undoing step being performed computationally in the acquired snapshot at a page level, said undoing step computationally producing an electronically accessible as-of snapshot which is a snapshot of the database as it existed at the as-of time;
and
handling an as-of query using a page which contains information responsive to the query, wherein the as-of query handling step comprises at least one of the following:
determining that the page which contains information responsive to the query is present in a sparse page file of the as-of snapshot;
determining that the page which contains information responsive to the query is not yet present in a sparse page file of the as-of snapshot, reading the page from the database, undoing modifications of the page back to the as-of time to produce an as-of page, and writing the as-of page to the sparse page file of the as-of snapshot;
or
sharing sparse file cache content among different as-of snapshots.

5 more elements

A computer system comprising:

at least one processor;
a memory in operable communication with the logical processor, the memory configured with data and with instructions that when executed by at least one processor causes the processor(s) to perform a process for accessing a version of database content as it existed at a previous point in time (the “as-of time”), the process comprising the steps of acquiring a database snapshot based on a database, undoing modifications of database content which were made after the as-of time, said undoing step being performed computationally in the acquired snapshot at a page level, said undoing step computationally producing an electronically accessible as-of snapshot which is a snapshot of the database as it existed at the as-of time, and handling an as-of query using a page which contains information responsive to the query, said as-of query handling comprising at least one of the following:
determining that the page which contains information responsive to the query is present in a sparse page file of the as-of snapshot;
determining that the page which contains information responsive to the query is not yet present in a sparse page file of the as-of snapshot,
reading the page from the database, undoing modifications of the page back to the as-of time to produce an as-of page, and writing the as-of page to the sparse page file of the as-of snapshot;
or
sharing sparse file cache content among different as-of snapshots;
a database snapshot residing in (and thus configuring) the memory, the database snapshot based on a database;
and
a list of page modifications residing in the memory and describing at a page level modifications made to the database after an as-of time.

7 more elements

Dependencies are inferred from the claim text.