Abstract: An improved concurrency control system for application to a distributed concurrent transaction and query processing system using multi-version database records to overcome delays arising from lock conflicts. Read-only queries are afforded a consistent "stable state" of the database during the life of the query. Updating transactions requiring locks can proceed without waiting for the termination of long queries. At least two database versions are necessary, although availability of more versions permits long read-only queries to phase-out over time without forcing new queries to use aged "stable-state" data and without roll-back. Read-only queries can be terminated and converted to locking transactions to permit an update of the "stable state" database version before the queries would normally terminate. A novel record key structure having a plurality of substructures corresponding to the several database versions is used to access database records.

Abstract: A fast method for sorting data in a distributed data processing system is disclosed. Each processor P.sub.1 12i locally sorts its data into a local sorted file S.sub.i 34i, simultaneously producing an index to the sorted data and a file of key data records R' 32 each comprising a key value paired with the processor's identifier. Each processor produces a distribution table DT.sub.i 28i of its key values using the index, and sends the table to acoordinator processor 18 which merges the processors' tables into a global distribution table GST 30. The global distribution table assigns subranges of key values to the processors, and is broadcast back to them. Each processor then sends each paired key value and processor identifier to the processor assigned by the global distribution table to handle the subrange containing that key value. The processors receive and merge the incoming key data records simultaneously as they send such pairs to other processors. An output stream V.sub.

Abstract: Weak synchronization and scheduling of each processor among concurrent asynchronous processors is governed by either task execution invoked by an external response indicating its low bid among the well-ordered set of most recently bid signals, task deferred until such indication is received from subsequent bid evaluations, or task aborted as by transfer to another task upon indication that an instantaneous bid was not the minimum.

Abstract: Flow graph related program segments having cyclic paths therethrough are efficiently processed on a SIMD machine by priority ordering the segments, selectively inserting ELSE/JOIN instructions as steps prior to enforcing the ordering when the network of program segments is executed on a SIMD machine.