Data Logging File Management - AutoDelete

Data logging sessions can produce a large number of data files and, if not managed, these files can use up all available space in the logging file system. The functions grouped under the name AutoDelete are designed to help control the space used by the files so as to minimize the chances of losing critical data files.

Either or both of these systems can be activated based on the needs of your particular installation.


Reserved Space AutoDelete

The Reserved Space AutoDelete system allows you to define a minimum amount of file system space which must be kept in reserve. When the available space drops below the given threshold, the oldest files in the file system will be deleted until the sufficient reserved space becomes available. The controls for Reserved Space AutoDeleting are available on the Data Logging - AutoDelete page. You can enable this form of Auto Deleting and set the threshold in Megabytes. When enabled, the system will check the available space at approximate one minute intervals.

The Reserved Space system removes files strictly based on their last-modification-times and regardless of whether the files are also managed in the Session Pool system. If both forms of file management are enabled at the same time, it is recommended that the Reserved Space system be treated as a backup to the Session Pool system.


Session Pool File Management

Session Pools are collections of files that can be managed independently from each other. The Pools are defined based on the Session Identifier character ('a' to 'z') selected when the Session was defined. This character is embedded as part of the name of every logged data file. You can define a Session Pool for any or all of the possible Sesssion Identifier characters. So, for example, there can be an a-pool, a b-pool, an x-pool, etc. A Default Pool is also available to manage all files which aren't contained in the other defined pools.

Each Session Pool is given a maximum size. When the file system space used by the files in a Pool exceeds the Pool's size, the Pool is said to have overflowed. When a Pool overflows, one of two things will happen:

The choice of which action to take on Pool Overflow is made by enabling or disabling AutoDelete for the Pool. If AutoDelete is disabled, then Session logging into an overflowing Pool will stop until some other action is taken that deletes files in the Pool. For example, the user could download files using FTP and then delete the files. When Pool overflow is no longer detected, the pending sessions will automatically restart.

Controls for Session Pools are available on the Data Logging - AutoDelete page. In the Session Pools section, you can

Pools that aren't explicitly defined do not exist. For example, if files are logged using the 'm' Session Identifier, and no m-pool is defined, then the Session Pool system will not manage those files. However, if the Default-pool is defined, it will manage the collection of all files that aren't contained in any other explicitly defined Pools.

Session Pool Managment is activated when one or more Pools are defined. When active, the entire logging file system is scanned approximately every minute to determine the current size of each pool. Any overflows are then acted upon by either deleting files or shutting down sessions. The status of all Pools can be viewed on the Data Logging Status page which shows, for each pool, the number of files, the current size, the maximum size, and the AutoDelete control setting. Pools that have overflowed are indicated with a blinking FULL indicator. Sessions that have been halted due to Pool overflows will show a status of Pending. Note that the Pool status information will not respond quickly to actions like manual file deletions, since the file system is only scanned every minute.

Pool membership is determined completely by the Session Identifier character embedded in each file's name. For example, in a file named "SN123777_200401052219m.BNX", the Session Identifier is 'm'. It is possible to have multiple Sessions defined that create files with the same Session Identifier. For example, you might want to collect data for one-hour, every day at 00:00, 08:00 and 16:00, that is, every eight hours. This would require creating three separate Daily Sessions. They could all be given an identical Session Identifier 'd'. There would be no conflict in doing so, since none of the three Sessions would ever be running at the same time. Giving them all a 'd' Session Identifer would allow all of these files to be managed in a single Session Pool.


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