A snapshot differential refresh algorithm

ABSTRACT

This article presents an algorithm to refresh the contents of database snapshots. A database snapshot is a read-only table whose contents are extracted from other tables in the database. The snapshot contents can be periodically refreshed to reflect the current state of the database. Snapshots are useful in many applications as a cost effective substitute for replicated data in a distributed database system. When the snapshot contents are a simple restriction and projection of a single base table, differential refresh techniques can reduce the message and update costs of the snapshot refresh operation. The algorithm presented annotates the base table to detect the changes which must be applied to the snapshot table during snapshot refresh. The cost of maintaining the base table annotations is minimal and the amount of data transmitted during snapshot refresh is close to optimal in most circumstances.

REFERENCES

• ADIBA 80: M E Achba and B G Lmdsay, Database Snapshots, Proceedings 6th International Conference on Very large Data Bases, Montreal, Canada (October 1980) pp 86-91
• HAAS 82: L M Haas, Pl Sehnger, E Bertmo, D Darnels, B Lmdsay, G Lohman, Y Masunaga, C Mohan, P Ng, P Wdms, and R Yost, R* A Research ProJect on Dtstnbuted Relatwnal DBMS, IEEE Database Engineering, Vol 5, No 4 (also available as IBM Research Report RJ3653, October 1982) (December 1982) pp 28-32
• LOHMAN 85: G Lohman, C Mohan, L Haas, D Danlels, B Lmdsay, P Selmger, and P Wdms, Query Processing m R *, m Query Processing m Database Systems, W Ktm, D Remer, and D Batory (Eds), Sprmger-Verlag, 1985 (also avadable as IBM Research Report RJ4272, Aprd 1984)

INDEX TERMS

Classification:
  E. Data
  E.1 DATA STRUCTURES
      Subjects: Tables**

  H. Information Systems
  H.2 DATABASE MANAGEMENT
      H.2.4 Systems
          Subjects: Query processing

General Terms:
Algorithms, Management