Table Characteristics

The Database Logger tables have the following characteristics:

Column Definitions

The following columns are defined for each type of log file:

Data logging tables contain a timestamp and Point ID column, plus an additional column for each table and point attribute you have selected. The number of columns is independent of the number of points in the table. For example, if you have a table that logs the point value and previous value for all points configured for data logging, the table will have four columns.

Alarm, Event, and Application logging tables have columns that are specific to that table, plus an additional column for each table attribute you have selected. All table rows include a timestamp column and an auto-increment sequence number that ensures that each row is unique.

Group logging tables contain a timestamp column, plus an additional column for each table and point attribute you have selected. For example, if you have a table logging the value and alarm state of five points, the table will have eleven columns.

image\Note.gif Note: Points with Engineering Units conversion are stored in floating point format

Key Definitions

The following keys are defined for each type of log file:

Group logging tables have a unique primary key index on the timestamp column. If you have selected the project name table attribute, the primary key index also includes the project name column.

Data logging tables have a primary key index on the joined timestamp and Point ID columns, and a secondary index on the timestamp alone. If you have selected the project name table attribute, the primary key index also includes the project name column.

Alarm, Event, and Application logging tables have a primary key index on the joined timestamp and sequence number columns, and a secondary index on the timestamp alone. If you have selected the project name table attribute, the primary key index also includes the project name column.

image\Important.gif Important: Since the Microsoft Access format and Oracle do not support sub-second timestamp data, you cannot log points to a Data or Group table at sub-second rates. Attempting to do so will cause the duplicate-keyed records to be dropped from the database.

More information

Create tables.

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About Database Logging management.