Abstract: A method and system for replicating database data is provided. One or more standby database replicas can be used for servicing read-only queries, and the amount of storage required is scalable in the size of the primary database storage. One technique is described for combining physical database replication to multiple physical databases residing within a common storage system that performs de-duplication. Having multiple physical databases allows for many read-only queries to be processed, and the de-duplicating storage system provides scalability in the size of the primary database storage. Another technique uses one or more diskless standby database systems that share a read-only copy of physical standby database files. Notification messages provide consistency between each diskless system's in-memory cache and the state of the shared database files.

Abstract: A computer is programmed to execute a diagnostic procedure either on a pre-set schedule or asynchronously in response to an event, such as an error message, or a user command. When executed, the diagnostic procedure automatically checks for integrity of one or more portions of data in the computer, to identify any failure(s). In some embodiments, the failure(s) may be displayed to a human, after revalidation to exclude any failure that no longer exists.

Abstract: Techniques are provided for using an intermediate cache between the shared cache of a database server and the non-volatile storage of a storage system. The intermediate cache may be local to the machine upon which the database server is executing, or may be implemented within the storage system. In one embodiment, the database system includes both a DB server-side intermediate cache, and a storage-side intermediate cache. The caching policies used to populate the intermediate cache are intelligent, taking into account factors that may include which database object an item belongs to, the item type of the item, a characteristic of the item; or the database operation in which the item is involved.

Abstract: A computer is programmed to automatically generate repairs to fix failure(s) while taking into account dependencies between repairs relative to one another, by grouping failures. In some embodiments, the computer uses a map that associates each failure type with repair types that are alternatives to one another, and uses another map that associates each repair type with a template that creates the repair when instantiated. In certain embodiments, repairs within a repair plan are consolidated, to avoid duplicates and redundancies.

Abstract: A standby database system or another replica data system replicates changes, made to data blocks at a source database system or another primary data copy, to replicas of the data blocks at the standby database system or other replica. While replicating the changes to the data blocks thereof, the standby database system (or other replica) receives queries (or reads) issued thereto and computes the queries based on data read from the data blocks thereof.

Abstract: Techniques are described herein for returning a repository to a prior state. The repository may be, for example a database, and the prior state may be, for example the consistent state that the database had at a particular point in time in the past. When a operator-caused error has been introduced to the database by changes made by an already-committed transaction, the techniques described herein may be used to recover from the error by returning the database to a point in time prior to the commit time of the transaction that introduced the error. The techniques involve the generation of “physical undo” information, and the use of the physical undo information in conjunction with physiological undo and physiological redo to efficiently return a repository to the prior state.

Abstract: Techniques are provided for detecting lost writes so that data corruption can be avoided. According to one technique, lost writes are detected by comparing version numbers that are indicated in redo log entries with version numbers that are indicated in corresponding blocks in a standby database. According to one technique, which may be used in conjunction with the above technique, lost writes are detected by logging read operations that occur relative to a primary database, and comparing version numbers that are indicated in read log entries with version numbers that are indicated in corresponding blocks in a standby database. According to one technique, lost writes are detected by comparing, in response to read operations, (a) version numbers that are stored in a persistent in-memory cache with (b) version numbers that are indicated in corresponding blocks that are read from a primary database.

Abstract: A method and apparatus for reducing down time in updating applications with metadata is provided. The application contains both code and metadata. A copy of the application is made. A software update is installed on the copy of the application. During installation, the original application continues to run and service users, who may modify the metadata of the original application. Periodically, the metadata of the copy of the application is updated to incorporate changes to the metadata of the original application. When the software update is completed, users are prevented from further modifying the metadata of the original application. The metadata of the copy of the application is updated to incorporate the final changes to the metadata of the original application. Users are redirected from the original application to the copy of the application.

Abstract: A computer is programmed to execute a diagnostic procedure either on a pre-set schedule or asynchronously in response to an event, such as an error message, or a user command. When executed, the diagnostic procedure automatically checks for integrity of one or more portions of data in the computer, to identify any failure(s). In some embodiments, the failure(s) may be displayed to a human, after revalidation to exclude any failure that no longer exists.

Abstract: A computer is programmed to identify failures and perform recovery of data. Specifically, in several embodiments, the computer is programmed to automatically check integrity of data in a storage structure to identify a set of failures related to the storage structure. The computer is further programmed in some embodiments to identify, based on one failure in the set of failures, a group of repairs to fix that one failure. Each repair in the group of repairs is alternative to another repair in the group. The computer is also programmed in some embodiments to execute at least one repair in the group of repairs, so as to generate corrected data to fix the one failure. In certain embodiments, the corrected data is stored in non-volatile storage media of the computer.

Abstract: A computer is programmed to automatically generate repairs to fix failure(s) while taking into account dependencies between repairs relative to one another, by grouping failures. In some embodiments, the computer uses a map that associates each failure type with repair types that are alternatives to one another, and uses another map that associates each repair type with a template that creates the repair when instantiated. In certain embodiments, repairs within a repair plan are consolidated, to avoid duplicates and redundancies.

Abstract: A standby database system or another replica data system replicates changes, made to data blocks at a source database system or another primary data copy, to replicas of the data blocks at the standby database system or other replica. While replicating the changes to the data blocks thereof, the standby database system (or other replica) receives queries (or reads) issued thereto and computes the queries based on data read from the data blocks thereof.

Abstract: A method and system for diagnostic preservation of the state of resources in a computer system after a failure is disclosed. An aspect of the invention is directed to the real-time diagnostic analysis of a computer system after a failure, in which the state of resources needed for the diagnostic analysis are preserved from the time of the failure. The computer system is then accessed by using other resources on the computer system, and the preserved resources are analyzed to debug the failure.

Abstract: Techniques are described herein for returning a repository to a prior state. The repository may be, for example a database, and the prior state may be, for example the consistent state that the database had at a particular point in time in the past. When a operator-caused error has been introduced to the database by changes made by an already-committed transaction, the techniques described herein may be used to recover from the error by returning the database to a point in time prior to the commit time of the transaction that introduced the error. The techniques involve the generation of “physical undo” information, and the use of the physical undo information in conjunction with physiological undo and physiological redo to efficiently return a repository to the prior state.

Abstract: A method and apparatus is provided for maintaining data integrity. According to the method, a physical checksum calculation is performed on a block of data. After performing the physical checksum calculation, a logical check is performed on the data contained with the block of data. If the block of data passes the logical check, then the block of data may be written to nonvolatile memory. Thereafter, when the block of data is read from nonvolatile memory a physical checksum verification procedure is performed on the block of data to determine whether the block of data was corrupted after performing the logical check on the data contained with the block of data.

Abstract: An approach for performing data block location verification includes inserting an address value into a data block that identifies a desired location in nonvolatile memory for storing the data block. Prior to performing an operation that stores the data block to the nonvolatile memory, a determination is made whether the address value in the data block correctly identifies the location in nonvolatile memory into which the operation will store the data block. The operation is performed only if the address value in the data block correctly identifies the location in nonvolatile memory into which the operation will store the data block. After the data block is read from the nonvolatile memory, an additional determination may be made to determine whether the data block was read from the desired location in the nonvolatile memory.

Abstract: Techniques are described herein for returning a repository to a prior state. The repository may be, for example a database, and the prior state may be, for example the consistent state that the database had at a particular point in time in the past. When a operator-caused error has been introduced to the database by changes made by an already-committed transaction, the techniques described herein may be used to recover from the error by returning the database to a point in time prior to the commit time of the transaction that introduced the error. The techniques involve the generation of “physical undo” information, and the use of the physical undo information in conjunction with physiological undo and physiological redo to efficiently return a repository to the prior state.

Abstract: A method and apparatus is provided for maintaining data integrity. According to the method, a physical checksum calculation is performed on a block of data. After performing the physical checksum calculation, a logical check is performed on the data contained with the block of data. If the block of data passes the logical check, then the block of data may be written to nonvolatile memory. Thereafter, when the block of data is read from nonvolatile memory a physical checksum verification procedure is performed on the block of data to determine whether the block of data was corrupted after performing the logical check on the data contained with the block of data.

Abstract: A system and method for detecting a failure of a first process is disclosed. According to one aspect, a first connection is established between a first process and a second process. A monitoring mechanism monitors the status of the first process to detect whether the first process has failed. In response to determining that the first process has failed, the monitoring mechanism causes an out-of-band message to be sent to the second process.

Abstract: An improved method, mechanism, and system for implementing, generating, and maintaining records, such as redo records and redo logs in a database system, are disclosed. Multiple sets of records may be created and combined into a partially ordered (or non-ordered) group of records, which are later collectively ordered or sorted as needed to create an fully ordered set of records. With respect to a database system, redo generation bottleneck is minimized by providing multiple in-memory redo buffers that are available to hold redo records generated by multiple threads of execution. When the in-memory redo buffers are written to a persistent storage medium, no specific ordering needs to be specified with respect to the redo records from the different in-memory redo buffers. While the collective group of records may not be ordered, the written-out redo records may be partially ordered based upon the ordered redo records from within individual in-memory redo buffers.