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Sort of Weekly Purging
Data retention policies can be confusing to understand. To make matters even worse, introducing weekly time periods to retention logic creates an unavoidable perception conflict. The way that purge schedule programming deals with this conflict is a somewhat subjective matter. Here is how “weekly” purge time periods are dealt with and represented within BitLeap®’s purge schedules.
The Problem
In order to understand how the actual weekly time period works and why it is appropriate to be setup this way, it is first important to grasp the problem that arises from using weekly time periods.
Weeks are a mess in a programming sense. While days always fit neatly into months and months always fit neatly into years, weeks can span across both the end of months and years. There is even disagreement across cultures on what specific day represents the start of a new week.
We will consider for the purposes of this demonstration a calendar week to always constitute beginning on Sunday at midnight and ending on Saturday night at 11:59:59 PM. Let us also assume that you want to purge out all but the latest file revision for each week during a part of your purge schedule. You then want to purge all but the latest file revision of each month for the next time period. When using a calendar week, your actual latest file revision of the month will be purged by your weekly purge settings for any month that does not end nice and neatly on a Saturday. When your monthly retention schedule kicks in, it will no longer have the latest revision of the month available to keep since it was purged by the preceding weekly schedule. Instead the latest revision in the month available will be last Saturday in the month.
Since weeks often span the calendar year boundary of December 31st, the same problem would occur if a weekly retention setting were applied before a yearly retention setting in the purge schedule. Being able to keep the actual latest revision of months and years is important functionality of a good data retention system. Therefore, BitLeap has introduced the following concept of weekly purging in order not to break the more important monthly and yearly schedules.
The Solution
Instead of Sunday through Saturday, weeks are considered periods of 7 days in a row beginning on the first of each month. According to the purge schedule the last “week” of the month may be 3, 2, 1 or actually 7 days long depending on the number of days (31, 30, 29, or 28 respectively) in the month.
Therefore, under a weekly retention setting, the purge schedule will keep the latest revision of the file for the greatest day in the week. For the first four 7 day periods, it will always keep the file revision from the 7th, 14th, 21st, and 28th day of the month. For months longer than 28 days, it will end up keeping the last day of the remaining week, which will always be the last day of the month. That way, when the potentially subsequent monthly or yearly retention schedule is applied, it will always have the latest revision of the month or year available for retention.
Questions about BitLeap’s purge scheduling should be directed to support@bitleap.com.