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AdministeringIn addition to administering the database server, you can tune performance, replicate data, and archive data.
System administrationThese topics contain concepts, procedures, and reference information for database and database server administrators to use for managing and tuning HCL OneDB™ database servers.
Performance GuideThe HCL OneDB™ Performance Guide describes how to configure and operate your HCL OneDB™ database server to improve overall system throughput and to improve the performance of SQL queries.
Queries and the query optimizerThese topics describe query plans, explain how the database server manages query optimization, and discuss factors that you can use to influence the query plan. These topics also describe performance considerations for SPL routines, the UDR cache, and triggers.
The query planThe query optimizer evaluates the different ways in which a query might be performed and determines the best way to select the requested data. During this evaluation, the optimizer formulates a query plan to fetch the data rows that are required to process a query.
The join planWhen a query contains more than one table, OneDB joins the tables using filters in the query. The way that the optimizer chooses to join the tables is the join plan.

The join plan

When a query contains more than one table, OneDB joins the tables using filters in the query. The way that the optimizer chooses to join the tables is the join plan.

In the following query, the customer and orders table are joined by the customer.customer_num = orders.customer_num filter:

SELECT * from customer, orders
WHERE customer.customer_num = orders.customer_num
AND customer.lname = "Higgins";

The join method can be a nested-loop join or a hash join.

Because of the nature of hash joins, an application with isolation level set to Repeatable Read might temporarily lock all the records in tables that are involved in the join, including records that fail to qualify the join. This situation leads to decreased concurrency among connections. Conversely, nested-loop joins lock fewer records but provide reduced performance when a large number of rows are accessed. Thus, each join method has advantages and disadvantages.