I as an ILM expert would say it is very important to have clear understanding on the ILM time definitions based on which further configurations are made in the system.
When you are configuring or using ILM scenarios, you will come across terms like residence period, retention period, expiration date, mandatory destruction date, etc. Here are some explanations on each of this and how they impact the ILM processes.
The relevant ILM terms are:
- Residence Period
- Retention Period
- Expiration Date
- Mandatory Destruction Date
- Time Reference
- Time Unit
- Time Offset
- Residence Period:
This is the time frame up to which you want to keep the data in DB. The time until the data should reside in DB and
NOT be archived. If this is defined, archiving of data will be done when this period is over. If a set of data does not complete this period, it will not be archived. This is defined by the ILM Residence Rules.
- Retention Period:
This is the time frame up to which the set of data has to be retained wherever that would be viz in DB or in archive file at ILM Store. This would define the validity of the data. A minimum value and a maximum value can be maintained in ILM rules.
With a reference date value and retention periods(min and max), expiration date and mandatory destruction date are determined. This is defined by ILM Retention Rules.
- Expiration Date
This is a date determined from the minimum retention period maintained in the ILM rule. This is set as property on the archive file when stored.
The data in DB or in archive file will
NOT be destroyed (permanent deletion) till we cross this date.
If an archive file has expiration date, then the file can only be destroyed when the expiration date is passed.
During calculation, if the expiration date is determined to be in the past, the expiration date of the archive file when storing would be set to today’s date. In this case archive file can be destroyed tomorrow.
Once the expiration date is set on archive file, it cannot be shortened. It can only be extended.
When multiple rules are valid for a set of data, then maximum value of the result set is set as expiration date.
- Mandatory Destruction Date
This is a date determined from maximum retention period maintained in ILM rule. This date would mean that the data
MUST be destroyed after this date.
When multiple rules are valid for a set of data, then minimum value of the result set is set.
- Time Reference
This value is to be maintained in ILM Rules. This would be the reference value used for residence and retention calculations in ILM. This would always be referencing to a date field.
- Time Unit
This value is to be maintained in ILM Rules. This is unit defined for the calculations. The values are Day/Month/Year.
- Time Offset
This value can be maintained in ILM rule. This would define if the resultant expiration date and mandatory destruction date should be adjusted for e.g. End of year.
If End of year is set, then the date would be changed to 31.12.YYYY with YYYY being the year determined via the ILM rule calculation.
With the above understanding, ILM rules can be easily maintained for the business and compliance requirements.
