10_Vertical_Partitioning

10_Vertical_Partitioning - Distributed Database Systems...

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Distributed Database Systems Vertical Partitioning 605.741 David Silberberg
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D. Silberberg Distributed Database Systems Vertical Partitioning 2 Vertical Fragmentation • Remember that R is broken into fragments R 1 , R 2 , … • Each contains attributes of R, plus the primary key (or an alternate identifier) to enable relation reconstruction • Vertical Fragmentation explored in single databases – Make queries more efficient – Fewer pages brought into memory – Most active fragments can be placed into faster, but more expensive, memory • RAM provides faster, but expensive, memory access • Disk provides slower, but cheaper, memory access
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D. Silberberg Distributed Database Systems Vertical Partitioning 3 Distributed Vertical Partitioning • Horizontal partitioning – If number of predicates = n, number of fragments can be 2 n minterm predicates – This occurs when each fragment is constrained by each minterm – However, some of these fragments are usually eliminated because they contradict some of the implications • Vertical partitioning is more complex – If number of non-key columns = m, the number of possible fragments is the m th Bell number B(m) m m for large m – This is a big number
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D. Silberberg Distributed Database Systems Vertical Partitioning 4 Example With two columns, the following potential fragmentation exists: – Therefore, B(2) = 2 With three columns, the following potential fragmentation exists: – Therefore, B(3) = 5 BA B A B A C C CB A CA B CBA C, B(2) CB, A | CA, B CBA BA | B, A
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D. Silberberg Distributed Database Systems Vertical Partitioning 5 Example - 4 Columns With four columns, the following potential fragmentation exists: BA B A C C CB A CA B DCBA D D D D D, B(3) B A DC DC, B(2) C A DB DB, B(2)
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D. Silberberg Distributed Database Systems Vertical Partitioning 6 Example - 4 Columns (cont.) – Therefore, B(4) = 15 CB C B DA DA, B(2) DCB A DCA B DCB,A | DCA,B DBA C DCBA DBA,C | DCBA
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D. Silberberg Distributed Database Systems Vertical Partitioning 7 Fragments With 5 Columns Frag(2) = B, A | BA – B(2) = 2 Frag(3) = C, Frag(2) | CB, A | CA, B | CBA – B(3) = 5 Frag(4) = D, Frag(3) | DC, Frag(2) | DB, Frag(2) | DA, Frag(2) | DCB, A | DCA, B | DBA, D | DCBA – B(4) = 15 Frag(5) = E, Frag(4) | ED, Frag(3) | EC, Frag(3) | EB, Frag(3) | EA, Frag(3) | EDC, Frag(2) | EDB, Frag(2) | EDA, Frag(2) | ECB, Frag(2) | ECA, Frag(2) | EBA, Frag(2) | EDCB, A | EDCA, B | EDBA, C | ECBA, D | EDCBA – B(5) = 52
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D. Silberberg Distributed Database Systems Vertical Partitioning 8 Fragmenting Many Columns How do we deal with the explosion of possibilities? We need heuristics – Heuristics do not explore every possibility so that we can find the optimal solution – They examine some possibilities that will likely lead to a good solution Two major classes of fragmentation heuristics – Grouping • Each attribute starts with its own fragment • Group them together when some criteria is met – Splitting • Start with a complete relation • Decide how to partition it after observing access patterns – Does not preclude a 3 rd way
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D. Silberberg Distributed Database Systems
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10_Vertical_Partitioning - Distributed Database Systems...

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