Query Processing and Optimization
Query Processing and Optimization
Query Processing and Optimization
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External or Disk-based Sorting, Cont.<br />
• Runs are now repeatedly merged<br />
• One memory buffer used to collect output<br />
r 1<br />
r 2<br />
•••<br />
Main Memory<br />
Buffer (N blocks)<br />
Output<br />
when merged<br />
m 1<br />
m 2<br />
•••<br />
Main Memory<br />
Buffer (N blocks)<br />
r N -1<br />
m last - 1<br />
•••<br />
r M div N<br />
output<br />
m last<br />
output<br />
r last<br />
sorted runs<br />
(N blocks each)<br />
Merged runs<br />
((M div N) div N-1) runs each of<br />
size N*N-1 blocks, <strong>and</strong> maybe one<br />
last run of < N*N-1 leftover blocks)<br />
17
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