Abstract: Techniques are described for storing and maintaining, in a materialized view, bitmap data that represents a bitmap of each possible distinct value of an expression and rewriting a query for a count of distinct values of the expression using the materialized view. The materialized view contains bitmap data that represents a bitmap of each possible distinct value of a first expression, and aggregate values of additional expressions, and is stored in memory or on disk by a database system. The database system receives a query that requests a number of distinct values, of the first expression, and an aggregate value for an additional expression. In response, the database system, rewrites the query to: compute the number of distinct values by counting the bits in the bitmap data of the materialized view that are set to the first value, and obtains the aggregate value for the additional expression in the materialized view.

Abstract: Embodiments generate random walks through a directed graph that is represented in a relational database table. Each row of the graph table represents a directed edge in the graph and includes a source vertex and a destination vertex. Each row is further augmented to (a) indicate the number of outbound edges starting from the destination vertex in the row and (b) include an identifier that distinguishes the edge from other outbound edges starting from the same source vertex. An SQL query may be executed on the augmented graph table. Starting from a source vertex (starting vertex or the destination vertex of the previously selected hop) the query randomly selects a row of the graph table representing one of the outbound edges from the source vertex and adds the selected outbound edge as a row in a random walk table that represents the next hop in the random walk.

Abstract: Techniques are presented herein for storing cursor duration temporary tables in memory of nodes in a clustered database system in association with iterations of an iterative query operation. The techniques involve associating a portion of memory with one or more iteration values. The iteration values indicate which iterations correspond to data that is stored in the portion of memory. When data is requested for a particular iteration, portions of memory are checked to determine if it stores the particular iteration.

Abstract: Techniques related to efficient data retrieval based on aggregate characteristics of composite tables are provided. A join zone map includes entries that describe data from a join relationship between a first key column of a first table and a second key column of a second table. The first table includes a dimension column. Each entry of the join zone map corresponds to a respective zone. Each zone includes contiguous data blocks that correspond to one or more second key column values. Each entry also includes a respective dimension value range of one or more dimension column values. Each dimension value range includes a respective maximum dimension value and a respective minimum dimension value. Furthermore, each entry includes a respective anti-join attribute value that indicates whether any of the one or more second key column values in a particular zone are non-null and fail to match any first key column values.

Abstract: Techniques are described herein for executing queries with a recursive clause using a plurality of processes that execute database operations in parallel. Each process of the plurality of processes either generate or are assigned a segment that is part of a temporary table. For each iteration of the recursive query, work granules are divided up and assigned to each of the plurality of processes. As each respective process produces a portion of a result set for a given iteration, that process appends said portion of the result set to the respective segment that the respective process manages. Each slave process then publishes, to one or more sources, a reference to the newly generated results. During the next iteration, any slave process may access any of the data from the previous iteration.

Abstract: Techniques are described herein to generate and to execute a query execution plan using static data buffering. After receiving a query with a clause that requires multiple iterations to execute, a database management system (DBMS) generates a plurality of plans that vary the order in which the database operations are executed. Within each plan, the DBMS identifies sets of rows within that plan that contain static data during execution of the query. Then, an additional step is added to each plan that includes loading the static set of rows in a database buffer cache. One or more database operations, from an iteration other than the first iteration, may be performed against the cached static set of rows. For each plan generated in this manner, a cost analysis model is applied, and the plan with the lowest estimated computational cost is selected for use as the query execution plan.

Abstract: Techniques are provided for using of zone maps to improve the performance of a much wider range of queries than those for which zone maps are currently used. Specifically, techniques are provided for using zone maps to improve performance of queries by providing aggregate values for a wide range of aggregate operations, including SUM, AVG, etc., providing aggregate values for aggregate queries that specify filter conditions, distinguishing between situations in which the aggregate values for a zone are invalid for pruning purposes and when the aggregate values are invalid for query-answering purposes, determining when aggregate values may be used in multi-table zone maps where the type of join specified by a query differs from the type of join used to generate the aggregate values in the zone map, and selecting among different aggregate values for the same zone based on the type of join specified in a query.

Abstract: Approaches, techniques, and mechanisms are disclosed for ensuring that a database command is executed according to a query plan that has been verified to be actually optimal. Except in rare circumstances, a database server does not execute a query plan unless it is first verified by the database server. The database server receives a request to execute a database command. The database server determines an unverified plan is the best plan for satisfying the request. Rather than risk the unknown behavior of an unverified plan, the database server instead satisfies the request according to a verified plan. Subsequently—for example as part of a scheduled job—the database server executes the unverified plan to determine performance statistics. Based at least on the performance statistics, the database server determines whether or not to verify the unverified plan. Techniques for concurrent and optimistic verifications are also disclosed.

Abstract: Techniques are provided for generating a “dimensional zonemap” that allows a database server to avoid scanning disk blocks of a fact table based on filter predicates in a query that qualify one or more dimension tables. The zonemap divides the fact table into sets of contiguous disk blocks referred to as “zones”. For each zone, a minimum value and a maximum value for each of one or more “zoned” columns of the dimension tables is determined and maintained in the zonemap. For a query that contains a filter predicate on a zoned column, the predicate value can be compared to the minimum value and maximum value maintained for a zone for that zoned column to determine whether a scan of the disk blocks of the zone can be skipped.

Abstract: Techniques related to efficient data retrieval based on aggregate characteristics of composite tables are provided. A join zone map includes entries that describe data from a join relationship between a first key column of a first table and a second key column of a second table. The first table includes a dimension column. Each entry of the join zone map corresponds to a respective zone. Each zone includes contiguous data blocks that correspond to one or more second key column values. Each entry also includes a respective dimension value range of one or more dimension column values. Each dimension value range includes a respective maximum dimension value and a respective minimum dimension value. Furthermore, each entry includes a respective anti-join attribute value that indicates whether any of the one or more second key column values in a particular zone are non-null and fail to match any first key column values.

Abstract: Computer systems, machine-implemented methods, and stored instructions are provided herein for maintaining information that describes aggregate characteristics of data within zones. Stored data may be separated into defined zone(s). Data structure(s), such as zone map(s), may store, for each of the zone(s), aggregate characteristic(s) of data in the zone, and a stored indication of whether or not the zone is stale. When a change is made to data in a particular zone that was not stale, a zone manager causes the particular zone to become stale if the change can result in the particular zone having data that is not included in the particular zone's stored aggregate characteristic(s). On the other hand, if the change cannot result in the particular zone having data that is not included in the particular zone's stored aggregate characteristic(s), then the zone manager does not cause the particular zone to become stale.

Abstract: Techniques are described herein to generate and to execute a query execution plan using static data buffering. After receiving a query with a clause that requires multiple iterations to execute, a database management system (DBMS) generates a plurality of plans that vary the order in which the database operations are executed. Within each plan, the DBMS identifies sets of rows within that plan that contain static data during execution of the query. Then, an additional step is added to each plan that includes loading the static set of rows in a database buffer cache. One or more database operations, from an iteration other than the first iteration, may be performed against the cached static set of rows. For each plan generated in this manner, a cost analysis model is applied, and the plan with the lowest estimated computational cost is selected for use as the query execution plan.

Abstract: Techniques are presented herein for storing cursor duration temporary tables in memory of nodes in a clustered database system in association with iterations of an iterative query operation. The techniques involve associating a portion of memory with one or more iteration values. The iteration values indicate which iterations correspond to data that is stored in the portion of memory. When data is requested for a particular iteration, portions of memory are checked to determine if it stores the particular iteration.

Abstract: Techniques are described herein for executing queries with a recursive clause using a plurality of processes that execute database operations in parallel. Each process of the plurality of processes either generate or are assigned a segment that is part of a temporary table. For each iteration of the recursive query, work granules are divided up and assigned to each of the plurality of processes. As each respective process produces a portion of a result set for a given iteration, that process appends said portion of the result set to the respective segment that the respective process manages. Each slave process then publishes, to one or more sources, a reference to the newly generated results. During the next iteration, any slave process may access any of the data from the previous iteration.

Abstract: Techniques for using zone map information for post index access pruning. In one embodiment, for example, a method for using zone map information for post index access pruning comprises: receiving a query statement comprising a first filter predicate on an indexed column of a database table and a second filter predicate on a zoned column of a database table; identifying zero or more pruneable zones of a zone map based on a value for the zoned column in the second filter predicate; obtaining a set of data record addresses from an index on the indexed column based on a value for the indexed column in the first filter predicate; and pruning, from access paths for processing the query statement, any data records, corresponding to data record addresses in the set of data record addresses, that are physically located in one of the pruneable zones.

Abstract: Techniques for partition pruning based on aggregated zone map information. In one embodiment, for example, a method for pruning partitions based on aggregated zone map information comprises: receiving a query statement comprising a filter predicate on a column of a database table; and pruning one or more partitions of the database table from access paths for processing the query statement based on determining, based on aggregated zone map information associated with the one or more partitions, that the filter predicate cannot be satisfied by data stored in the one or more partitions.

Abstract: Techniques are provided that address the problems associated with prior approaches for clustering a fact table in a relational database management system. According to one aspect of the invention, a database server clusters a fact table in a database based on one or more dimension tables. More specifically, rows are stored in the fact table in a sorted order and the order in which the rows are sorted is based on values in one or more columns of one or more of the dimension tables. A user specifies the columns of the dimension tables on which the sorted order is based in “clustering criteria”. The database server uses the clustering criteria to automatically store the rows in the fact table in the sorted order in response to certain user-initiated database operations on the fact-table.

Abstract: Approaches, techniques, and mechanisms are disclosed for maintaining a set of baseline query plans for a database command. Except in rare circumstances, a database server may only execute a command according to a baseline plan, even if the database server predicts that a different plan has a lower cost. The set of baseline plans are plans that, for one reason or another, have been determined to provide acceptable actual performance in at least one execution context. When the database server receives a request to execute a particular command, the database server, if possible, always executes the command according to the lowest predicted cost baseline plan. The database server may evolve the plan baseline to include additional plans by generating and testing new plans in response to new requests to execute the database command, or as part of a query optimization or tuning process.

Abstract: Techniques for partition pruning based on aggregated zone map information. In one embodiment, for example, a method for pruning partitions based on aggregated zone map information comprises: receiving a query statement comprising a filter predicate on a column of a database table; and pruning one or more partitions of the database table from access paths for processing the query statement based on determining, based on aggregated zone map information associated with the one or more partitions, that the filter predicate cannot be satisfied by data stored in the one or more partitions.

Abstract: Techniques for using zone map information for post index access pruning. In one embodiment, for example, a method for using zone map information for post index access pruning comprises: receiving a query statement comprising a first filter predicate on an indexed column of a database table and a second filter predicate on a zoned column of a database table; identifying zero or more pruneable zones of a zone map based on a value for the zoned column in the second filter predicate; obtaining a set of data record addresses from an index on the indexed column based on a value for the indexed column in the first filter predicate; and pruning, from access paths for processing the query statement, any data records, corresponding to data record addresses in the set of data record addresses, that are physically located in one of the pruneable zones.