EFFICIENT IN-MEMORY DB QUERY PROCESSING OVER ANY SEMI-STRUCTURED DATA FORMATS

摘要

Techniques are described herein for maintaining two copies of the same semi-structured data, where each copy is organized in a different format. One copy is in a first-format that may be convenient for storage, but inefficient for query processing. For example, the first-format may be a textual format that needs to be parsed every time a query needs to access individual data items within a semi-structured object. The database system intelligently loads semi-structured first-format data into volatile memory and, while doing so, converts the semi-structured first-format data to a second-format. Because the data in volatile memory is in the second-format, processing queries against the second-format data both allows disk I/0 to be avoided, and increases the efficiency of the queries themselves. For example, the parsing that may be necessary to run a query against a cached copy of the first-format data is avoided.

主权项

1. A method comprising:
maintaining, by a database server, a set of first-format data; wherein the database server maintains the set of first-format data on persistent storage; wherein the set of first-format data:
is accessible to the database server,represents a set of semi-structured documents, andis stored in a first-format; converting, by the database server, the set of first-format data to a second-format to produce a set of second-format data; wherein the second-format is one of:
a row-based mirror format;a set-based mirror format; ora master-detail mirror format; wherein the database server maintains the set of second-format data in volatile memory; wherein the second-format is different from and independent of the first-format; wherein the set of second-format data is accessible to the database server; the database server maintaining the set of second-format data transactionally consistent with the set of first-format data as the database server executes database operations that make changes to the set of first-format data; receiving, by the database server, a request to execute a database command that requires particular information from the set of semi-structured documents; and in response to receiving the request, the database server executing the database command; wherein, during execution of the database command, the database server obtains at least some of the particular information from the set of second-format data.