ΜΕΛΕΤΗ ΤΗΣ ΑΠΟΔΟΣΗΣ ΕΛΕΓΧΟΥ ΣΥΓΧΡΟΝΙΣΜΟΥ ΣΕ ΚΑΤΑΝΕΜΗΜΕΝΕΣ ΒΑΣΕΙΣ ΔΕΔΟΜΕΝΩΝ ΜΕ ΧΡΟΝΟΓΡΑΜΜΑΤΟΣΗΜΑ: ΤΕΛΕΙΑ ΚΑΙ ΜΗ ΤΕΛΕΙΑ ΡΟΛΟΓΙΑ

Abstract

THIS THESIS PRESENTS A MODEL OF A DISTRIBUTED DATABASE SYSTEM WHICH PROVIDES THE FRAMEWORK TO STUDY THE PERFORMANCE OF TIMESTAMP ORDERING CONCURRENCY CONTROL. LOCKING AND TIMESTAMPING ARE TWO POPULAR APPROACHES TO CONCURRENCY CONTROL IN DATABASES SYSTEMS. TIMESTAMP-BASED ALGORITHMS HAVE BEEN PROPOSED TO PROTECT DISTRIBUTED DATABASE FROM INCONSISTENCIES DURING CONCURRENT ACCESS. IN SUCH ALGORITHMS, TRANSACTIONS MAY REACH A PARTICULAR SITE OUT OF THE ORDEROF THEIR TIMESTAMPS, DUE TO UNEXPECTED NETWORK DELAYS. THIS CAUSES CONFLICTS WHICH THE DISTRIBUTED CONCURRENCY CONTROL MECHANISM HAS TO COPE WITH. WE EXHIBIT AN ANALYTICAL SOLUTION, WHICH HAS BEEN TESTED WITH EXTENSIVE SIMULATION. THE ACCURACY SEEMS TO BE VERY HIGH. WE ASSUME PERFECT AND ALSO IMPERFECT CLOCKS FOR SYNCHRONIZATION AND QUANTIFY THE WAY IN WHICH LOCAL CLOCK INACCURACIES AFFECT THE PHENOMENON OF TRANSACTION CONFLICTS. IN PARTICULAR, WE DERIVE A LOT OF INTERESTING PERFORMANCE MEASURES SUCH AS PROBABILITY OF ABORT, MEAN WAITING TIME, THROUGHPUT, MEAN QUEUE LENGTH AND OTHERS.