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外汇市场交易最主要的8种货币

Simple Sidebar

The starting state of the menu will appear collapsed on smaller screens, and will appear non-collapsed on larger screens. When toggled using the button below, the menu will change.

Make sure to keep all page content within the #page-content-wrapper . The top navbar is optional, and just for demonstration. Just create an element with the #sidebarToggle ID which will toggle the menu when clicked.

Up-to-date cache with EclipseLink and Oracle

Up-to-date cache with EclipseLink and Oracle

One of the most useful feature provided by ORM libraries is a second-level cache, usually called L2. L2 object cache reduces database access for entities and their relationships. It is enabled by default in the most popular JPA implementations like Hibernate or EclipseLink. That won’t be a problem, unless a table inside a database is not modified directly by third-party applications, or by the other instance of the same application in a clustered environment. One of the available solutions to this problem is in-memory data grid, which stores all data in a memory, and is distributed across many nodes inside a cluster. Such a tools like Hazelcast or Apache Ignite has been described several times in my blog. If you are interested in one of that tools I recommend you read one of my previous article bout it: Hazelcast Hot Cache with Striim.

However, we won’t discuss about it in this article. Today, I would like to talk about Continuous Query Notification feature provided by Oracle Database. It solves a problem with updating or invalidating a cache when the data changes in the database. Oracle JDBC drivers provide support 外汇市场交易最主要的8种货币 for it since 11g Release 1. This functionality is based on receiving invalidation events from the JDBC drivers. Fortunately, EclipseLink extends that feature in their solution called EclipseLink Database Change Notification. In this article I’m going to show you how to implement it using Spring Data JPA together with EclipseLink library.

How it works

The most useful functionality provided by the Oracle Database Continuous Query Notification is an ability to raise database events when rows in a table were modified. It enables client applications to register queries with the database and receive notifications in response to DML or DDL changes on the objects associated with the queries. To detect modifications, EclipseLink DCN uses Oracle ROWID to intercept changes in the table. ROWID is included to all queries for a DCN-enabled class. EclipseLink also retrieves ROWID of saved entity after an insert operation, and maintains a cache index on that ROWID. It also selects the database transaction ID once for each transaction to avoid invalidating the cache during the processing of transaction.

When a database sends a notification it usually contains the followoing information:

  • Names of the modifying objects, for example a name of changed table
  • Type of change. The 外汇市场交易最主要的8种货币 possible values are INSERT, UPDATE,DELETE, ALTER TABLE, or DROP TABLE
  • Oracle’s ROWID of changed record

Running Oracle database locally

Before starting working on our sample application we need to have Oracle database installed. Fortunately, there are some Docker images with 外汇市场交易最主要的8种货币 Oracle Standard Edition 12c. The command visible below starts Oracle XE version and exposes it on default 1521 port. It is also possible to use web 外汇市场交易最主要的8种货币 console available under port 9080.

Simple Sidebar

The starting state of the menu will appear collapsed on smaller screens, and will appear non-collapsed on larger screens. When toggled using the button below, the menu will change.

Make sure to keep all page content within the #page-content-wrapper . The top navbar is optional, and just for demonstration. Just create an element with the #sidebarToggle ID which will toggle the menu when clicked.

Simple Sidebar

The starting state of the menu will appear collapsed on 外汇市场交易最主要的8种货币 smaller screens, and will appear non-collapsed on larger screens. When toggled using the button below, the menu will change.

Make sure to keep all page content within the #page-content-wrapper . The top navbar is optional, and just for demonstration. Just create an element with the #sidebarToggle ID 外汇市场交易最主要的8种货币 which will toggle the menu when clicked.