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Parallel Databases - Coggle Diagram

- - - - A transaction locks the page in
        shared or exclusive mode before any read or write
      - Before a transaction releases an exclusive lock on a page, it flushes the page to the shared disk
- - - - Tuples of a relation are divided among many disks, so that each tuple resides on one disk.
  - - - best suited for point queries based on
        the partitioning attribute
    - - well suited for point and range queries on
        the partitioning attribute
    - - suited for applications that wish to read
        the entire relation sequentially for each query
  - - - Some values appear in the partitioning attributes of many tuples
    - - refers to the fact that there may be load imbalance in the partitioning
- - - - We can speed up processing of a query by parallelizing the execution of each individual operation, like sort, select, project, and join.
    - - We can speed up processing of a query by executing in parallel the different operations in a query expression.
- - - - Can be performed as tuples are read in from disk in parallel
    - - Can be parallelize by partitioning the relation on the grouping attributes, and then computing the aggregate values locally at each processor
    - - Can be eliminated by sorting; either of the parallel sort techniques can be used, optimized to eliminate duplicates as soon as they appear during sorting
  - - - first range partitioning the relation, then sorting each partition separately
    - - Each processor Pi locally sorts the data on disk Di, then the system merges the sorted runs on each processor to get the final sorted output