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Buffer Pool (cont)

How scans are performed with Buffer Pool: 

Buffer buf;
int N = numberOfBlocks(Rel);
for (i = 0; i < N; i++) {
   pageID = makePageID(db,Rel,i);
   bufID = request_page(pageID);
   buf = frames[bufID]
   for (j = 0; j < nTuples(buf); j++)
      process(buf, j)
   release_page(pageID);
}

Requires N page reads on the first pass.

If we read it again, 0 ≤ page reads ≤ N