Abstract: Techniques are provided for automatic verification of query results obtained from data formatted different from row-major format. Techniques are also provided for automatic triage of query results obtained from data formatted different from row-major format. In an embodiment, the query results may be obtained from querying data formatted in column-major format. In an embodiment, when the query results are determined to be incorrect, a cause of the error in the query results can be automatically identified.

Abstract: Techniques are introduced herein for maintaining geometry-type data on persistent storage and in memory. Specifically, a DBMS that maintains a database table, which includes at least one column storing spatial data objects (SDOs), also maintains metadata for the database table that includes definition data for one or more virtual columns of the table. According to an embodiment, the definition data includes one or more expressions that calculate minimum bounding box values for SDOs stored in the geometry-type column in the table. The one or more expressions in the metadata maintained for the table are used to create one or more in-memory columns that materialize the bounding box data for the represented SDOs. When a query that uses spatial-type operators to perform spatial filtering over data in the geometry-type column is received, the DBMS replaces the spatial-type operators with operators that operate over the scalar bounding box information materialized in memory.

Abstract: A “hybrid derived cache” stores semi-structured data or unstructured text data in an in-memory mirrored form and columns in another form, such as column-major format. The hybrid derived cache may cache scalar type columns in column-major format. The structure of the in-memory mirrored form of semi-structured data or unstructured text data enables and/or enhances access to perform path-based and/or text based query operations. A hybrid derived cache improves cache containment for executing query operations. The in-memory mirrored form is used to compute queries in a transactionally consistent manner through the use of an invalid vector that used to determine when to retrieve the transactionally consistent persistent form of semi-structured data or unstructured text data in lieu of the in-memory form.

Abstract: Techniques are described herein for maintaining two copies of the same semi-structured data, where each copy is organized in a different format. One copy is in a first-format that may be convenient for storage, but inefficient for query processing. For example, the first-format may be a textual format that needs to be parsed every time a query needs to access individual data items within a semi-structured object. The database system intelligently loads semi-structured first-format data into volatile memory and, while doing so, converts the semi-structured first-format data to a second-format. Because the data in volatile memory is in the second-format, processing queries against the second-format data both allows disk I/O to be avoided, and increases the efficiency of the queries themselves. For example, the parsing that may be necessary to run a query against a cached copy of the first-format data is avoided.

Abstract: Techniques are described for maintaining an expression statistics store that stores and updates metadata values for query expressions based on the occurrence of those query expressions within queries. In an embodiment, a database server instance receives a database query. In response, the database server instance identifies expressions within the database queries. The database server instance then determines whether an expression statistics store includes an entry for the particular expression. Responsive to determining that the expression statistics store includes an entry for the particular expression, the database server instance updates at least one metadata value in the entry based on the occurrence of the particular expression. Responsive to determining that the expression statistics store does not include an entry for the particular expression, the database server instance adds an entry for the particular expression.

Abstract: Techniques are described for materializing computations in memory. In an embodiment, responsive to a database server instance receiving a query, the database server instance identifies a set of computations for evaluation during execution of the query. Responsive to identifying the set of computations, the database server instance evaluates at least one computation in the set of computations to obtain a first set of computation results for a first computation in the set of computations. After evaluating the at least one computation, the database server instance stores, within an in-memory unit, the first set of computation results. The database server also stores mapping data that maps a set of metadata values associated with the first computation to the first set of computation results.

Abstract: Techniques are described for materializing computations in memory. In an embodiment, responsive to a database server instance receiving a query, the database server instance identifies a set of computations for evaluation during execution of the query. Responsive to identifying the set of computations, the database server instance evaluates at least one computation in the set of computations to obtain a first set of computation results for a first computation in the set of computations. After evaluating the at least one computation, the database server instance stores, within an in-memory unit, the first set of computation results. The database server also stores mapping data that maps a set of metadata values associated with the first computation to the first set of computation results.

Abstract: Techniques are provided for automatic verification of query results obtained from data formatted different from row-major format. Techniques are also provided for automatic triage of query results obtained from data formatted different from row-major format. In an embodiment, the query results may be obtained from querying data formatted in column-major format. In an embodiment, when the query results are determined to be incorrect, a cause of the error in the query results can be automatically identified.

Abstract: Techniques are provided for automatic verification of query results obtained from data formatted different from row-major format. Techniques are also provided for automatic triage of query results obtained from data formatted different from row-major format. In an embodiment, the query results may be obtained from querying data formatted in column-major format. In an embodiment, when the query results are determined to be incorrect, a cause of the error in the query results can be automatically identified.

Abstract: Techniques related to cache storage formats are disclosed. In some embodiments, a set of values is stored in a cache as a set of first representations and a set of second representations. For example, the set of first representations may be a set of hardware-level representations, and the set of second representations may be a set of non-hardware-level representations. Responsive to receiving a query to be executed over the set of values, a determination is made as to whether or not it would be more efficient to execute the query over the set of first representations than to execute the query over the set of second representations. If the determination indicates that it would be more efficient to execute the query over the set of first representations than to execute the query over the set of second representations, the query is executed over the set of first representations.

Abstract: Techniques are described for materializing pre-computed results of expressions. In an embodiment, a set of one or more column units are stored in volatile or non-volatile memory. Each column unit corresponds to a column that belongs to an on-disk table within a database managed by a database server instance and includes data items from the corresponding column. A set of one or more virtual column units, and data that associates the set of one or more column units with the set of one or more virtual column units, are also stored in memory. The set of one or more virtual column units includes a particular virtual column unit storing results that are derived by evaluating an expression on at least one column of the on-disk table.

Abstract: Techniques are described herein for maintaining two copies of the same semi-structured data, where each copy is organized in a different format. One copy is in a first-format that may be convenient for storage, but inefficient for query processing. For example, the first-format may be a textual format that needs to be parsed every time a query needs to access individual data items within a semi-structured object. The database system intelligently loads semi-structured first-format data into volatile memory and, while doing so, converts the semi-structured first-format data to a second-format. Because the data in volatile memory is in the second-format, processing queries against the second-format data both allows disk I/0 to be avoided, and increases the efficiency of the queries themselves. For example, the parsing that may be necessary to run a query against a cached copy of the first-format data is avoided.

Abstract: Techniques are described for materializing pre-computed results of expressions. In an embodiment, a set of one or more column units are stored in volatile or non-volatile memory. Each column unit corresponds to a column that belongs to an on-disk table within a database managed by a database server instance and includes data items from the corresponding column. A set of one or more virtual column units, and data that associates the set of one or more column units with the set of one or more virtual column units, are also stored in memory. The set of one or more virtual column units includes a particular virtual column unit storing results that are derived by evaluating an expression on at least one column of the on-disk table.

Abstract: Techniques are described for maintaining an expression statistics store that stores and updates metadata values for query expressions based on the occurrence of those query expressions within queries. In an embodiment, a database server instance receives a database query. In response, the database server instance identifies expressions within the database queries. The database server instance then determines whether an expression statistics store includes an entry for the particular expression. Responsive to determining that the expression statistics store includes an entry for the particular expression, the database server instance updates at least one metadata value in the entry based on the occurrence of the particular expression. Responsive to determining that the expression statistics store does not include an entry for the particular expression, the database server instance adds an entry for the particular expression.

Abstract: Techniques are described for materializing computations in memory. In an embodiment, responsive to a database server instance receiving a query, the database server instance identifies a set of computations for evaluation during execution of the query. Responsive to identifying the set of computations, the database server instance evaluates at least one computation in the set of computations to obtain a first set of computation results for a first computation in the set of computations. After evaluating the at least one computation, the database server instance stores, within an in-memory unit, the first set of computation results. The database server also stores mapping data that maps a set of metadata values associated with the first computation to the first set of computation results.

Abstract: Techniques are provided for automatic verification of query results obtained from data formatted different from row-major format. Techniques are also provided for automatic triage of query results obtained from data formatted different from row-major format. In an embodiment, the query results may be obtained from querying data formatted in column-major format. In an embodiment, when the query results are determined to be incorrect, a cause of the error in the query results can be automatically identified.