Figure
14 shows the schema of a node X with availability-related replica from another
node Y. Notice that some relations are already replicated by placement (S and C).
Node X can now replace node Y in case of unavailability of Y by simply including
Y partitions in the processing.
The simplest replica placement strategy involves replicating each node??™s data into
at least one other node??”full replicas (FRs). In case of failure of one node, a node
containing the replica resumes the operation of the failed node. A simple placement
algorithm considering R replicas is:
Number nodes linearly;
For each node i
For (replica =1 to R) data for node i is also placed in node (i+R) MOD N;
G1 G2 G3 G4
Partitioned Partitioned + Medium
Replicated Partitioned + Large Replicated Partitioned + Large Replicated +
Medium Replicated
Q1, Q6, Q15 Q11,Q14,Q19 Q3, Q5, Q7, Q9, Q10, Q12, Q16 Q4, Q8, Q13, Q22
Figure 12. Size and layout of relations involved in parallel join over PRS
Figure 13. Grouped speedup results for PRS and WBP over 25 nodes
0
0
20
0
40
G :Part t oned G2:Part t oned +
Medium
Replicated
G :Part t oned +
Large Replicated
G :Part t oned +
Large Replicated
+ Medium
Replicated
Speedup / 25
PRS WBP
Efficient and Robust Node-Partitioned Data Warehouses 22
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