Offset Pushdown for Multipart Database Sorting
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Solution Overview
Problem
Database management systems face challenges in optimizing performance when handling complex queries with offset and limit clauses, particularly due to the high computational and memory costs associated with merging intermediate result sets from multiple database shards.
Innovation Solution
A method is introduced to detect select queries with order by, offset, and limit clauses, determining a modified offset by subtracting the size of the smaller dataset from the original offset, and executing the query on the larger dataset using this modified offset to reduce the number of comparisons and intermediate results, thereby optimizing runtime and resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the select query is executed on multiple database shards and intermediate result sets are merged, then the query can access distributed data, but the computational and memory costs increase significantly
Solution Approach 1:
The patent applies preliminary action by calculating the modified offset value before executing the select query on database shards. The query optimizer determines the size of smaller intermediate result sets in advance and uses this information to adjust the offset value, thereby avoiding unnecessary data retrieval and merging operations, which reduces computational and memory costs while maintaining distributed data access capability
Solution Approach 2:
The patent extracts and eliminates unnecessary intermediate result sets through modified offset pushdown. By calculating the effective offset after accounting for smaller dataset sizes, the system removes redundant data that would otherwise be retrieved, merged, and then discarded, thus reducing the computational burden of merging operations
2Speed
If the offset value is pushed down to database shards, then query execution can skip unnecessary rows, but the offset calculation becomes more complex when merging multiple result sets
Solution Approach 1:
The patent changes the offset parameter dynamically based on the sizes of intermediate result sets from different database shards. The query optimizer calculates a modified offset value that accounts for the cumulative size of smaller datasets, transforming the simple offset pushdown into an adaptive parameter adjustment that maintains execution speed while handling merge complexity
Solution Approach 2:
The patent implements feedback by using information about intermediate result set sizes to adjust the offset calculation. The query optimizer receives feedback about the actual or estimated sizes of datasets from different shards and uses this feedback to compute the modified offset value, creating a closed-loop system that optimizes query execution
3Manufacturing precision
If all intermediate result sets are merged before applying offset and limit, then the result ordering is correct, but the processing time and memory usage increase
Solution Approach 1:
The patent applies preliminary action by determining the modified offset value before executing the query and merging operations. The query optimizer calculates how many rows can be skipped in advance based on the sizes of smaller intermediate result sets, allowing the system to maintain correct result ordering while avoiding the time-consuming process of merging all intermediate results before applying offset and limit
Data Source
AI summary
In some aspects, a method, computer program product, and system are provided for query optimization. In some implementations, there may be provided a method including detecting a select query as a candidate for optimization, the select query including an order by, an offset value, and a limit value; determining, in response to the detecting, a modified offset value as the difference between the offset value and a size of a smaller dataset; and performing the select query to form a result set, the select query executed based on at least the modified offset value. Related systems, methods, and articles of manufacture are also described.