| 摘要 |
SQL queries are optimized to operate directly on compressed data (and obtain the correct result) rather than requiring that the data be first decompressed prior to processing a query. Certain characteristic pattern trees are mapped against a logical input query plan that includes certain logical operators such as a DECOMPRESS that precedes a JOIN or a GROUPBY in association with a COUNT to identify instances in the plan that match a characteristic pattern. Upon locating a match, the input query plan is transformed into a logically equivalent plan that operates correctly on compressed data, by analyzing the interplay of the semantics of logical query operations with the compressed data and substituting less costly structures and operations. DECOMPRESS operations are moved to operate subsequent to a JOIN or eliminated altogether, and COUNT operations are replaced by a different operation, such as SUM, that is logically equivalent for compressed data. |
| 主权项 |
1. A computer-implemented method comprising:
receiving a query plan that includes a first pattern of query operators that (i) includes a decompress query operator followed by another query operator, and (ii) is configured to operate directly on decompressed data; determining that the first pattern of query operators that (i) includes the decompress query operator followed by the other query operator, and (ii) is configured to operate directly on decompressed data, matches a second pattern of one or more query operators that (i) does not include a decompress query operator, and (ii) is configured to operate directly on compressed data; obtaining a transformed query plan by replacing, in the query plan, the first pattern of query operators that (i) includes the decompress operator followed by the other query operator, and (ii) is configured to operate on decompressed data, with the second pattern of one or more query operators that (i) does not include the decompress query operator, and (ii) is configured to operate directly on compressed data; and executing the transformed query plan, including executing the second pattern of one or more query operators that (i) does not include the decompress operator, and (ii) is configured to operate directly on compressed data, on compressed data. |
