US 7,548,919 B2Granted

Computer program product for conducting a lock free read

AssigneeInternational Business Machines Corporation

InventorsMonish Gupta, Scott David Lashley

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Abstract

The present invention expounds upon the ANSI “read committed” isolation level by allowing readers to read committed data without waiting for a concurrent writer to the data to finish. The method returns a last committed version of the data as it existed prior to changes made by the concurrent writer. Only two versions of any data record are required to be stored in the record data store, the last committed version and the current version. The last committed version may be generated from an undo log record. Locating the appropriate undo log record may be accomplished by storing a log sequence number in a lock data structure associated with the requested data record. A transaction flag may also stored in the lock data structure to facilitate generating the last committed version. The method may also utilize one or more locks to detect a concurrent writer to the requested data.

Claims7

Dependent claims

A computer program product comprising a computer readable storage medium having computer usable program code programmed and executed by a processor for conducting a lock free read, the operations of the computer program product comprising:

receiving a write transaction request on a record, the received write transaction request comprising at least a first operation on the record and a second operation on the record;
conducting a two-phase exclusive-lock locking procedure for the received write transaction request on the record using a lock data structure, wherein the lock data structure includes a last committed log sequence number and a transaction flag for the record, the transaction flag indicating whether the transaction corresponding to the last committed log sequence number is an insert operation, an update operation, or a delete operation, and wherein the last committed log sequence number points to data corresponding to a last committed version of the record;
performing the first operation of the transaction on the record, and committing a corresponding change to the record;
updating the last committed log sequence number and the transaction flag, wherein the updated last committed log sequence number points to the committed corresponding change to the record and the updated transaction flag indicates whether the performed first operation is an insert operation, an update operation, or a delete operation;
receiving a read transaction request for the record;
generating an updated last committed version of the record based on the updated last committed log sequence number and the updated transaction flag in response to receiving the read transaction request, the updated last committed version of the record that is generated comprising the committed corresponding change to the record;
returning the updated last committed version of the record that is generated in response to the read transaction request, and
performing the second operation on the record and releasing the two-phase exclusive-lock locking procedure.

5 more elements

receiving a write transaction request on a record, the received write transaction request comprising at least a first operation on the record and a second operation on the record;
conducting a two-phase exclusive-lock locking procedure for the received write transaction request on the record using a lock data structure, wherein the lock data structure includes a last committed log sequence number and a transaction flag for the record, the transaction flag indicating whether the transaction corresponding to the last committed log sequence number is an insert operation, an update operation, or a delete operations, and wherein the last committed log sequence number points to data corresponding to a last committed version of the record;
performing the first operation of the transaction on the record, and committing a corresponding change to the record;
updating the last committed log sequence number and the transaction flag, wherein the updated last committed log sequence number points to the committed corresponding change to the record and the updated transaction flag indicates whether the performed first operation is an insert operation, an update operation, or a delete operation;
receiving a read transaction request for the record;
generating an updated last committed version of the record based on the updated last committed log sequence number and the updated transaction flag in response to receiving the read transaction request, the updated last committed version of the record that is generated comprising the committed corresponding change to the record in response to the updated transaction flag indicating an update transaction or a delete transaction;
returning the updated last committed version of the record that is generated in response to the read transaction request;
and
performing the second operation on the record and releasing the two-phase exclusive-lock locking procedure.

6 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/534,564Filed 22 Sep 2006
Published: US 2008/0077591 A127 Mar 2008
Granted: 16 Jun 2009
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

G06F 9/466
Multiprogramming arrangements: transaction processing
G06F 16/2343
Pessimistic concurrency control approaches, e.g. locking or multiple versions without time stamps: locking methods, e.g. distributed locking or…
Y10S 707/99938
Database or file accessing: concurrency, e.g. lock management in shared database
G06F
Computing and data processing