Abstract: A multiprocessor that includes a virtual file system providing a file system interface to user application code. This interface allows users to access files in many types of file systems in a consistent, file system-independent manner. In a preferred embodiment, the higher interface of the file system is the Posix file system interface, though it can be any file system interface supporting the capabilities required by a user process. The Posix file system supports regular files, pipes, fifos and special files.A pipe server, a pipe library and a name server together implement the fifo semantics required by the Posix standard for Posix processes. The present invention provides these fifo capabilities to any process which uses the Posix interfaces.

Abstract: A cache is distributed among processors in a multiple processor system with no shared memory to maintain the cached data. Each processor maintains a cache which identifies the opened files being cached, the blocks of each file which are cached and the state of caching for each file. The state of each opened file is one of "no-caching", "read-caching" and "read/write caching". So long as only one processor opens a file, and opens it for read/write access, that processor is allowed to do read/write caching on the file. When a processor opens a file for read access, that processor is allowed to do read caching, unless another processor has the file open for read/write access. After the last processor having read/write access to a file closes the file, the disk system upgrades the cache state for the file.

Abstract: An improved recovery method utilizes sequence numbers to order log records and reduce the excess compensating actions due to a failure during recovery. Next undo records are written to the log after a preset number of compensating actions which include the sequence number of the record currently being scanned. After a failure, all records between the next undo record and the record having the sequence number included in the next undo record are ignored during when the log is scanned backwards.

Abstract: An SQL program executor and an SOL compiler both include options for avoiding recompilations of execution plans whenever the runtime object and the compile time object referenced by an execution plan meet predefined schema similarity criteria. Thus, recompilation is sometimes avoided even though the compile time object has been altered or the run time object is not the same object as the compile time object. To enable late binding, schema information is stored in each execution plan for each object to be accessed by the execution plan. The stored schema information is a subset of the full object schema, and includes information about all the aspects of the objects to be accessed which must remain unchanged in order for the execution plan to be operable. While executing a compiled program, the SQL executor avoids recompilations of execution plans whenever the runtime object and the compile time object referenced by an execution plan meet predefined schema similarity criteria.