分区对以下查询“从表名中选择*”有什么影响？

Question

I have implemented database partitioning on my database. The partitioning is done by DBMS_REDEFINITION. The question in my mind is when we execute the select * statement from the table does the partitioning affect the performance.

Tip: We are selecting entire data of a table

What is the difference between select * from Non_Partitioned_table and select * from Partitioned_table ?

Answer 1

Partitioning is unlikely to have any affect on a query like select * from table_name;

It won't help performance.

A common misconception about partitioning is that simply dividing the table into chunks improves performance. Unless you are taking advantage of a specific partitioning feature, such as partition pruning or partition-wise joins, it's much better to let Oracle decide how to divide the work. For example, with parallel processing, Oracle can just as easily divide up the work into block range granules instead of partition granules.

It probably won't hurt performance.

There's a little extra overhead with parsing; more metadata to gather and analyze, more optimizer decisions to evaluate. In practice I've never noticed a significant difference just from partitioning. I've definitely seen some unusual behavior with complex partition pruning decisions, but that's not relevant to this simple statement.

There's a little extra data to read; more segments may mean more wasted space. In practice, with defaults and a normal number of partitions, this extra overhead is not a big deal. Especially with deferred segment creation , where an empty partition takes up 0 bytes. Although that feature only works with partitions starting with 11.2.0.2.

But things can go very poorly in some extreme examples. For example, if you set a large and uniform extent size, or disable deferred segment creation, or create a table with thousands of partitions each with only a single row. In that case, a simple select statement could takes minutes instead of a fraction of a second.