Abstract:
Techniques for processing “destructive” database statements are provided. Destructive database statements, when processed, cause metadata of a database object to be changed. Examples of such database statements include ones that delete an index, that set a column as unused, and that drop a constraint on a column. When such a statement is received, a change is made to metadata of a database object. Such a metadata change may involve setting an index as unusable, disabling a constraint, or invalidating a cursor. After the metadata change, a first time is determined. Then, it is determined when one or more database transactions that were pending at the first time have committed. After those database transaction(s) have committed, one or more operations are performed, such as dropping an index or dropping a constraint.
Abstract:
Techniques for creating and using partial indexes are provided. A partial index is an index that indexes one or more partitions of a partitioned table and does not index one or more other partitions of the partitioned table. Thus, if a partition of a partitioned table is rarely used, then an index may index all other partitions of the partitioned table or at least only those partitions that are written to or read from relatively frequently. Also, in preparation for loading data into a partition, indexing for the partition may be “turned off”, effectively making a full index a partial index. While the data is loaded into the partition, the partial index is still available for query processing. After the data is loaded into the partition, indexing for the partition is “turned on”, which causes the data in the partition to be indexed by the partial index.
Abstract:
Techniques are described herein for creating a new database table for an exchange operation with a table partition of another table. A database management system (DBMS) is configured to receive a query such as “CREATE TABLE new_table FOR EXCHANGE FROM partition_P1”. The DBMS then identifies properties of the source partition (e.g., partition P1) and creates a new database table based on the properties identified. Some of these properties (e.g., hidden columns, data modeling frameworks, and table statistics) may not otherwise be directly accessible by the external entity that sent the query. The newly created table then has all of the necessary properties to be part of the other table if swapped with the source partition in an exchange operation.
Abstract:
Techniques are provided for moving data between partitions. Such a process may be performed without requiring any locks that block transactions that target a partition from being executed. Instead, such transactions may proceed while a move operation is being performed. The move operation involves copying data from the targeted partition to another partition that is hidden from (or “invisible” to) those transactions that attempt to read from or write to the partition. During the move operation, changes that are made to the partition are also reflected in a journal. Eventually, the changes reflected in the journal are drained and applied to the hidden partition. Once the partition and the hidden partition are synchronized, the identities of the partitions are swapped so that future transactions will target the previously-hidden partition instead of the previously-viewable partition.
Abstract:
Techniques are provided for moving data between partitions. Such a process may be performed without requiring any locks that block transactions that target a partition from being executed. Instead, such transactions may proceed while a move operation is being performed. The move operation involves copying data from the targeted partition to another partition that is hidden from (or “invisible” to) those transactions that attempt to read from or write to the partition. During the move operation, changes that are made to the partition are also reflected in a journal. Eventually, the changes reflected in the journal are drained and applied to the hidden partition. Once the partition and the hidden partition are synchronized, the identities of the partitions are swapped so that future transactions will target the previously-hidden partition instead of the previously-viewable partition.
Abstract:
Techniques for processing “destructive” database statements are provided. Destructive database statements, when processed, cause metadata of a database object to be changed. Examples of such database statements include ones that delete an index, that set a column as unused, and that drop a constraint on a column. When such a statement is received, a change is made to metadata of a database object. Such a metadata change may involve setting an index as unusable, disabling a constraint, or invalidating a cursor. After the metadata change, a first time is determined. Then, it is determined when one or more database transactions that were pending at the first time have committed. After those database transaction(s) have committed, one or more operations are performed, such as dropping an index or dropping a constraint.
Abstract:
Techniques are described herein for creating a new database table for an exchange operation with a table partition of another table. A database management system (DBMS) is configured to receive a query such as “CREATE TABLE new_table FOR EXCHANGE FROM partition_P1”. The DBMS then identifies properties of the source partition (e.g., partition P1) and creates a new database table based on the properties identified. Some of these properties (e.g., hidden columns, data modeling frameworks, and table statistics) may not otherwise be directly accessible by the external entity that sent the query. The newly created table then has all of the necessary properties to be part of the other table if swapped with the source partition in an exchange operation.
Abstract:
Techniques are provided for moving data between partitions. Such a process may be performed without requiring any locks that block transactions that target a partition from being executed. Instead, such transactions may proceed while a move operation is being performed. The move operation involves copying data from the targeted partition to another partition that is hidden from (or “invisible” to) those transactions that attempt to read from or write to the partition. During the move operation, changes that are made to the partition are also reflected in a journal. Eventually, the changes reflected in the journal are drained and applied to the hidden partition. Once the partition and the hidden partition are synchronized, the identities of the partitions are swapped so that future transactions will target the previously-hidden partition instead of the previously-viewable partition.
Abstract:
Techniques for maintaining a global index in response to a partition being dropped are provided. In response to an instruction to drop a partition, partition identification data that identifies the partition is stored. Index entries, in the global index, that correspond to the dropped partition become “orphaned” entries. Later, an execution plan for a query is processed, where the execution plan targets a global index. During execution of the execution plan, one or more index entries are accessed. For each accessed index entry, the partition identification data is analyzed to determine if the index entry is an orphaned entry. If so, then the index entry is ignored for purposes of the query. Later, the global index may be updated to delete each orphaned entry. Such deletion may occur much later, such as during a time when the database is not queried or updated frequently.
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.