Responsibility of Transparency
- Transparency is desirable but there is a compromise between level of Transparency and difficulty/cost
- The language/Compiler: to provide uniform method of manipulating data. Avoid connectivity details.
- Operating System: already provides in form of Device Drivers
- Can also provide network Trns. However not all provide complete.
- Third layer is DBMS. Uses features of Operating System in particular for network transparency.
- Practically, we get combination of all three.
Layers of Transparency
Reliability in DDBS
- Reliability through Distributed Transactions: Avoids simple point of failure
- Concurrency Issues: Transaction involving multiple records
- Failure Recovery: Involving multiple sites
Performance Improvement
- Through Data Localization
- Each site handles a portion of data, so contention of CPU or I/O is relatively less
- Reduces remote access delays; no matter how fast networks are latency delays are there and may be unacceptable in certain case
- Inter-query and Intra-query parallelism
Complicating Factors
- In case of Replication:
- Choose the appropriate copy
- Update impact reflected on all replicas
- Failure Recovery
- Complexity
- Cost: hardware and also the duplication of manpower
- Distribution of Control may cause problems if not used cautiously
The Problem Areas
- Database Design
- Query Processing
- Concurrency Control
- OS Support
- Heterogeneity
- Relationship among them
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