Persistent version storage for relational database management system

A method for implementing persistent version storage, comprising:

• providing a storage policy, wherein the storage policy comprises at least one in-row scheme rule that defines when to store previous version information within a payload of a row of a database page, wherein the at least one in-row scheme rule defines that the previous version information is stored within the payload of the row of the database page when a difference between a previous version of the row and a current version of the row is less than a defined threshold, wherein the row includes the current version of the row, wherein the storage policy further comprises at least one off-row scheme rule that defines when to store the previous version information, wherein the at least one off-row scheme rule defines that the previous version information is stored in an off-row page separate from the database page when the difference between the previous version of the row and the current version of the row is greater than the defined threshold, and wherein the previous version information comprises information regarding the previous version of the row within the database page;
• storing the previous version information within the payload of the row of the database page when the at least one in-row scheme rule is satisfied;
• and
• storing the previous version information in the off-row page when the at least one off-row scheme rule is satisfied;
• and
• determining a minimum useful transaction identifier for the relational database system;
• comparing a transaction identifier associated with the first row with the minimum useful transaction identifier;
• and
• deleting the previous version information if the transaction identifier is less than the minimum useful transaction identifier.

A relational database system that implements persistent version storage, comprising:

• one or more processors;
• memory in electronic communication with the one or more processors;
• a plurality of database pages stored in the memory;
• a storage policy stored in the memory, wherein the storage policy comprises at least one in-row scheme rule that defines when an in-row scheme is utilized to store previous version information, and wherein the storage policy further comprises at least one off-row scheme rule that defines when an off-row scheme is utilized to store the previous version information, wherein the previous version information comprises information regarding a previous version of a row of a database page;
• instructions stored in the memory, the instructions being executable by the one or more processors to:
• store the previous version information within a payload of the row of the database page in accordance with the in-row scheme when an in-row scheme rule is satisfied;
• and
• store the previous version information in an off-row page in accordance with the off-row scheme when an off-row scheme rule is satisfied, wherein the off-row page is separate from the database page;
• determine a minimum useful transaction identifier;
• compare a transaction identifier associated with the row with the minimum useful transaction identifier;
• delete the previous version information if the transaction identifier is less than the minimum useful transaction identifier;
• and
• at least one page free space (PFS) page stored in the memory, wherein the at least one PFS page comprises a record indicating whether the database page contains any previous version information stored in the payload of the row within the database page and wherein the row includes a current version of the row.