mirror of
https://github.com/janishutz/eth-summaries.git
synced 2026-07-27 21:29:09 +02:00
16 lines
853 B
TeX
16 lines
853 B
TeX
\subsubsection{Index Matching}
|
|
The predicates in the queries can contain comparison operators, as well as \texttt{AND} and \texttt{OR}, allowing conjuncts and disjuncts.
|
|
|
|
Index Matching is the process of choosing the proper index for the task.
|
|
For conjuncts only, we can use:
|
|
\begin{itemize}
|
|
\item \bi{Hash Indexes}. Constraints: Only equality operations and predicate has to contain all index attributes
|
|
\item \bi{B+-Tree}. Constraints: The attributes in the predicates need to be prefixes of the search key
|
|
\end{itemize}
|
|
|
|
Here, the indexes need to match \bi{every} predicate in the disjunction.
|
|
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|.
|
|
In that case, we can either file scan or use both indexes (we fetch the RIDs and take the union)
|
|
|
|
However, index matching is a hard problem.
|