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16 lines
853 B
TeX
16 lines
853 B
TeX
\subsubsection{Index Matching}
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The predicates in the queries can contain comparison operators, as well as \texttt{AND} and \texttt{OR}, allowing conjuncts and disjuncts.
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Index Matching is the process of choosing the proper index for the task.
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For conjuncts only, we can use:
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\begin{itemize}
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\item \bi{Hash Indexes}. Constraints: Only equality operations and predicate has to contain all index attributes
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\item \bi{B+-Tree}. Constraints: The attributes in the predicates need to be prefixes of the search key
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\end{itemize}
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Here, the indexes need to match \bi{every} predicate in the disjunction.
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For instance, if we have a hash index on $A$ and a B+ tree on $B$, and the query is \verb|A = 7 OR B > 5|.
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In that case, we can either file scan or use both indexes (we fetch the RIDs and take the union)
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However, index matching is a hard problem.
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