Prior to Oracle Database 10g, if youchanged the location referenced by a synonym,
you would have to recompile any PL/SQL procedures that accessed the synonym.
Clusters
A cluster is a data structure that improves retrieval performance. A cluster, like an
index, does not affect the logical view of the table.
A cluster is a way of storing related data values together on disk. Oracle reads data a
block at a time, so storing related values together reduces the number of I/O operations
needed to retrieve related values, since a single data block will contain only
related rows.
A cluster is composed of one or more tables. The cluster includes a cluster index,
which stores all the values for the corresponding cluster key. Each value in the cluster
index points to a data block that contains only rows with the same value for the
cluster key.
If a cluster contains multiple tables, the tables should be joined together and the
cluster index should contain the values that form the basis of the join. Because the
value of the cluster key controls the placement of the rows that relate to the key,
changing a value in that key can cause Oracle to change the location of rows associated
with that key value.
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