Parallel Sort


Parallel Sort
Range-Partitioning Sort
􀂄 Choose processors P0, ..., Pm, where m ≤ n -1 to do sorting.
􀂄 Create range-partition vector with m entries, on the sorting attributes
􀂄 Redistribute the relation using range partitioning
􀃌 all tuples that lie in the ith range are sent to processor Pi
􀃌 Pi stores the tuples it received temporarily on disk Di.
􀃌 This step requires I/O and communication overhead.
􀂄 Each processor Pi sorts its partition of the relation locally.
􀂄 Each processors executes same operation (sort) in parallel with other
processors, without any interaction with the others (data parallelism).
􀂄 Final merge operation is trivial: range-partitioning ensures that, for 1 j
m, the key values in processor Pi are all less than the key values in Pj.

Parallel Sort (Cont.)
Parallel External Sort-Merge
􀂄 Assume the relation has already been partitioned among disks
D0, ..., Dn-1 (in whatever manner).
􀂄 Each processor Pi locally sorts the data on disk Di.
􀂄 The sorted runs on each processor are then merged to get the
final sorted output.
􀂄 Parallelize the merging of sorted runs as follows:
􀃌 The sorted partitions at each processor Pi are range-partitioned
across the processors P0, ..., Pm-1.
􀃌 Each processor Pi performs a merge on the streams as they are
received, to get a single sorted run.
􀃌 The sorted runs on processors P0,..., Pm-1 are concatenated to get
the final result.

Comments

Post a Comment

Popular posts from this blog

Handling of Skew

Handling of Skew 􀂄 The distribution of tuples to disks may be skewed — that is, some disks have many tuples, while others may have fewer tuples. 􀂄 Types of skew: 􀃌 Attribute-value skew. 􀂾 Some values appear in the partitioning attributes of many tuples; all the tuples with the same value for the partitioning attribute end up in the same partition. 􀂾 Can occur with range-partitioning and hash-partitioning. 􀃌 Partition skew. 􀂾 With range-partitioning, badly chosen partition vector may assign too many tuples to some partitions and too few to others. 􀂾 Less likely with hash-partitioning if a good hash-function is chosen. Handling Skew in Range-Partitioning 􀂄 To create a balanced partitioning vector (assuming partitioning attribute forms a key of the relation): 􀃌 Sort the relation on the partitioning attribute. 􀃌 Construct the partition vector by scanning the relation in sorted order as follows. 􀂾 After every 1/nth of the relation has been read, the value...
Read more

Fragment-and-Replicate Join

Fragment-and-Replicate Join 􀂄 Partitioning not possible for some join conditions 􀃌 e.g., non-equijoin conditions, such as r.A > s.B. 􀂄 For joins were partitioning is not applicable, parallelization can be accomplished by fragment and replicate technique 􀃌 Depicted on next slide 􀂄 Special case – asymmetric fragment-and-replicate: 􀃌 One of the relations, say r, is partitioned; any partitioning technique can be used. 􀃌 The other relation, s, is replicated across all the processors. 􀃌 Processor Pi then locally computes the join of ri with all of s using any join technique. 􀂄 General case: reduces the sizes of the relations at each processor. 􀃌 r is partitioned into n partitions,r0, r1, ..., r n-1;s is partitioned into m partitions, s0, s1, ..., sm-1. 􀃌 Any partitioning technique may be used. 􀃌 There must be at least m * n processors. 􀃌 Label the processors as 􀃌 P0,0, P0,1, ..., P0,m-1, P1,0, ..., Pn-1m-1. 􀃌 Pi,j computes the join of ri with sj. In ...
Read more

USER INTERFACE DESIGN FOR ANNA UNIVERSITY SYLLABUS

Unit – I Introduction Objective To Understand the definition and importance of User Interface Design To know about the concept, advantages and applications of GUI and Web interface User Interface Design Definition • User interface design is a subset of a field of study called human-computer interaction (HCI). Human-computer interaction is the study, planning, and design of how people and computers work together so that a person’s needs are satisfied in the most effective way. • The user interface is the part of a computer and its software that people can see, hear, touch, talk to, or otherwise understand or direct. The user interface has essentially two components: input and output. • Input is how people communicate his needs to the system using keyboard or any pointing device and output is how the system returns processing result to user through screen or sound. • The best interface is one which has proper design with combination of effective input and output mechanisms. Importance of...
Read more