Structure Query Language (SQL): Chapter 3 – Data Discard and DB Limits.

There is an important tool in Elipse E3 to help monitor a database, called data discard (available when setting up Historics, Storages, and Alarm Tables). This option enables data discard in the main table. Therefore, the data’s age is determined by what is set up in Keep recorded data from the last option. This field corresponds to EnableDiscard property.

The Discarded data must be stored option allows storing discarded data in the secondary table (backup table). This field corresponds to EnableBackupTable property.

Figure 1 – Data discard

You choice of database will depend directly on its purposes; however, we strongly recommend using at least a SLQ or Oracle Express (Free) database. Microsoft Access database is used only for smaller applications.

Database size limits

• SQL EXPRESS 2012 SP1: supports 1 CPU, 1GB RAM, and can store up to 10 GB per DB.
• ORACLE EXPRESS EDITION 11g Release 2 (XE): supports 1 CPU, 1GB RAM, and can store up to 10 GB per DB.
• ACCESS: can store no more than 2 GB, and its security system is not 100% reliable (can be sort of unstable over 100 MB).

The SQL Express and Oracle XE databases, with less storage space, can have their use also monitored, nonetheless. The article Checking the space being used by an SQL database demonstrates how to check the size in an SLQ Server database.

In a company, there are usually a great number of Microsoft Access databases in all levels, many of which will become critical mission. It is crucial that these databases be protected against data losses and changes, and that their performance not be below what is expected.

To reach a satisfactory level of service, these applications must be hosted centrally in a robust server platform, such as  Microsoft SQL Server or Oracle.

The main reasons to upgrade from Microsoft Access to a more robust database are: more reliability, more scalability, more security, better performance, easier maintenance, and better manageability.