Oracle 12c-对于具有分区和子分区的表，应使用哪个索引

Question

I have a table of 500M records in Oracle 12c. Table is partitioned per 1 varchar column and sub-partitioned per other varchar column.

What indexes should be used with queries that use these 2 columns in Where clause?

I am assuming local partitioned indexes are the best choice but wanted to get more insight on when is this a case and how is the best to create them?

Answer 1

Oracle is capable of partition pruning , meaning that if your query has the partition key column(s) in the where clause, Oracle is smart enough to only query those partitions that are relevant. In such case a local partitioned index is more beneficial because it is "local to the partition", ie the index is also partitioned the same way and Oracle will only read the relevant index entries for those partition that are relevant.

If however you have a query that doesn't have the partition key column(s) in the where clause Oracle can't apply partition pruning and will have no other choice but to scan all local partitioned indexes or, worst case, the entire table for the data. This is where a global partitioned index will come in handy on those columns that are in the where clause. In that case Oracle creates an index over those columns across partitions and knows exactly which records to read from which partitions that qualify for the where clause of the statement.