Preview abstract
Business intelligence and web log analysis workloads often use queries with top-k clauses to produce the most relevant results. Values of k range from small to rather large and sometimes the requested output exceeds the capacity of the available main memory. When the requested output fits in the available memory existing top-k algorithms are efficient, as they can eliminate almost all but the top k results before sorting them. When the requested output exceeds the main memory capacity, existing algorithms externally sort the entire input, which can be very expensive. Furthermore, the drastic difference in execution cost when the memory capacity is exceeded results in an unpleasant user experience. Every day, tens of thousands of production top-k queries executed on F1 Query resort to an external sort of the input.
To address these challenges, we introduce a new top-k algorithm that is able to eliminate parts of the input before sorting or writing them to secondary storage, regardless of whether the requested output fits in the available memory. To achieve this, at execution time our algorithm creates a concise model of the input using histograms. The proposed algorithm is implemented as part of F1 Query and is used in production, where significantly accelerates top-k queries with outputs larger than the available memory. We evaluate our algorithm against existing top-k algorithms and show that it reduces I/O traffic and can be up to 11× faster.View details
Preview abstract
F1 Query is a stand-alone, federated query processing platform that executes SQL queries against data stored in different file-based formats as well as different storage systems (e.g., BigTable, Spanner, Google Spreadsheets, etc.). F1 Query eliminates the need to maintain the traditional distinction between different types of data processing workloads by simultaneously supporting: (i) OLTP-style point queries that affect only a few records; (ii) low-latency OLAP querying of large amounts of data; and (iii) large ETL pipelines transforming data from multiple data sources into formats more suitable for analysis and reporting. F1 Query has also significantly reduced the need for developing hard-coded data processing pipelines by enabling declarative queries integrated with custom business logic. F1 Query satisfies key requirements that are highly desirable within Google: (i) it provides a unified view over data that is fragmented and distributed over multiple data sources; (ii) it leverages datacenter resources for performant query processing with high throughput and low latency; (iii) it provides high scalability for large data sizes by increasing computational parallelism; and (iv) it is extensible and uses innovative approaches to integrate complex business logic in declarative query processing. This paper presents the end-to-end design of F1 Query. Evolved out of F1, the distributed database that Google uses to manage its advertising data, F1 Query has been in production for multiple years at Google and serves the querying needs of a large number of users and systems.View details