Systems use a Global Conceptual Schema (GCS) that maps logical tables to physical fragments. Solutions often involve "Transparent Mapping," where the query optimizer automatically decomposes a global query into sub-queries targeted at specific nodes. This ensures that the user's SQL remains identical regardless of where the data resides. Data Fragmentation and Allocation
The Two-Phase Commit (2PC) protocol is blocking. If the coordinator crashes while participants are in the READY state, those participants must block and wait until the coordinator recovers to resolve the transaction.
Suppose we have a distributed database system with two nodes, each storing a different fragment of a large database. We want to execute a transaction that updates the customer address on Node 1 and also updates the corresponding order information on Node 2.
What happens if the coordinator fails after the voting phase? Solution: This is the "blocking problem" of 2PC. Participants may be left in an uncertain state, holding locks indefinitely until the coordinator recovers. This is why modern systems often look toward Three-Phase Commit (3PC) or Paxos/Raft consensus algorithms. 5. Parallelism and Data Replication Systems use a Global Conceptual Schema (GCS) that
Derive the fragmentation for ASG such that the assignments are stored at the same site as the project they belong to.
VF partitions a relation by its attributes based on attribute affinity. Given an Attribute Affinity matrix ( AAcap A cap A
We can fragment the database into three fragments: Data Fragmentation and Allocation The Two-Phase Commit (2PC)
Distributed concurrency control ensures transaction atomicity and isolation across multiple sites.
The distributed query can be written as:
Replication is the process of maintaining multiple copies of data at different sites to improve availability and performance. We want to execute a transaction that updates
provides structured summaries of the principles discussed in the text. 3. Alternative Practice Resources
Reliability exercises often focus on what happens when a site or a link fails during a transaction. The 2PC Protocol Steps:
The tuple with SAL = 30000 is excluded, violating the completeness rule. The correct predicates are SAL ≥ 30000 and SAL < 30000 (or SAL > 30000 and SAL ≤ 30000 ) to include the borderline case.
Strict 2PL (all locks held until commit/abort) avoids this because T1 doesn’t release X lock before committing, so T2 can’t read X until T1 commits → no cycle.
Design a fragmentation strategy to ensure that London projects are only in London and New York projects are only in New York.