摘要:
Provided are a techniques for processing a query including semi-joins. At execution time, a next semi-join is selected from the semi-joins for execution in a current round of semi-join executions. A reporting threshold is determined that indicates a number of record-identifiers to be retrieved for the determined semi-join. The selected semi-join is executed until the determined number of record identifiers are retrieved.
摘要:
Provided are a techniques for processing a query including semi-joins. At execution time, a next semi-join is selected from the semi-joins for execution in a current round of semi-join executions. A reporting threshold is determined that indicates a number of record-identifiers to be retrieved for the determined semi-join. The selected semi-join is executed until the determined number of record identifiers are retrieved.
摘要:
A method, computer program product, and system for managing row identifier (RID) list processing on an index are provided. The method, computer program product, and system provide for accessing one or more key values in the index based on one or more keys specified in a query, retrieving a plurality of row identifiers corresponding to the one or more key values from the index, and predicting an actual number of row identifiers to be retrieved from the index based on the one or more key values accessed and the plurality of row identifiers retrieved.
摘要:
A method, computer program product, and system for managing row identifier (RID) list processing on an index are provided. The method, computer program product, and system provide for accessing one or more key values in the index based on one or more keys specified in a query, retrieving a plurality of row identifiers corresponding to the one or more key values from the index, and predicting an actual number of row identifiers to be retrieved from the index based on the one or more key values accessed and the plurality of row identifiers retrieved.
摘要:
A method, computer program product, and system for processing dynamic statements in a database system are provided. The method, computer program product, and system provide for calculating a first set of characteristics associated with a dynamic statement when the dynamic statement matches one of a plurality of dynamic statements previously processed by the system, comparing the first set of characteristics associated with the dynamic statement to a second set of characteristics associated with one of one or more access paths generated for the one previously processed dynamic statement, and utilizing the one access path to execute the dynamic statement when the comparison of the first set of characteristics to the second set of characteristics satisfies one or more predetermined criteria.
摘要:
Embodiments of the present invention provide a “look-ahead” form prefetch. Look-ahead prefetch may utilize a look-ahead queue to prefetch multiple pages asynchronously. The look-ahead queue may hold a plurality of search keys that are related to a transaction. When accessing a table, an index manager may retrieve the table's index and scan the index based on the search keys from the look-ahead queue to find the RIDs in the table that match the search keys. The index manager may then accumulate these RIDs into a prefetch list. A prefetch manager may read the prefetch list, determine locations for the pages of the table that contain the records identified by the RIDs, and dispatch prefetch tasks to the appropriate storage device for these pages.
摘要:
A method, apparatus, and article of manufacture for optimizing a query in a computer system, wherein the query is performed by the computer system to retrieve data from a database stored on the computer system. The optimization comprises determining an optimal access plan for a first-N-rows query by evaluating a cost of fetching N rows, relative to a total number of rows R in a final results set. Specifically, for a pipelined access plan, this comprises calculating how many rows need to be fetched from each table in the pipelined plan in order to obtain the first N rows from the final results set.
摘要:
A database query is partitioned into an initial partition including a plurality of parallel groups, and is executed, via an execution plan, based on the initial partition. A sampling subset of data is identified from the plurality of parallel groups. Substantially in parallel with the executing of the query, the execution plan is executed on the sampling subset of data as a sampling thread. The execution plan is modified based on feedback from the execution of the execution plan on the sampling subset of data.
摘要:
A database query is partitioned into an initial partition including a plurality of parallel groups, and is executed, via an execution plan, based on the initial partition. A sampling subset of data is identified from the plurality of parallel groups. Substantially in parallel with the executing of the query, the execution plan is executed on the sampling subset of data as a sampling thread. The execution plan is modified based on feedback from the execution of the execution plan on the sampling subset of data.
摘要:
A method, storage server, and computer readable medium for off-loading star-join operations from a host information processing system to a storage server. At least a first and second set of keys from a first and second dimension table, respectively are received from a host system. Each of the first and second set of keys is associated with at least one fact table. A set of locations associated with a set of foreign key indexes are received from the host system. A set of fact table indexes are traversed. At least a first set of Row Identifiers (“RIDs”) associated with the first set of keys and at least a second set of RIDs associated with the second set of keys are identified. An operation is performed on the first and second sets of RIDs to identify an intersecting set of RIDs. The intersecting set of RIDs are then stored.