Key Considerations for Snapshots
Ensure that you make a note of the following considerations when using snapshots for historical item retrievals.
Storage Requirements
The snapshots feature requires additional database storage capacity for storing snapshots in the table. The storage requirements depend on the frequency of snapshot generation, the number of fields in the system, and the data type of the fields. For example, if there are significant number of text fields in the system and if the snapshots are generated frequently, the storage requirement is high. If the snapshot generation frequency is low, the storage requirement is low.
Hence, ensure that there is enough space available in the database before you begin using the snapshot feature.
Enable snapshot generation when there are no snapshots generated in the system
If an administrator enables snapshot generation when the number of edits for an item exceed the snapshot generation frequency value, the system generates the snapshots at the very next edit that matches the frequency along with the previous missing snapshots.
For example, consider an item having 4900 edits. If the snapshot generation frequency is set to 1000, then at the 5000th edit, the system generate a total of 5 snapshots. The first at the 1000th edit, the second at the 2000th, the third at the 3000th edit, the fourth at the 4000th edit, and the fifth at the 5000th edit.
Change the snapshot generation frequency
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Before changing the frequency of snapshot generation ensure that you have tested snapshot generation with the required frequency on a test setup. Once you are satisfied with the results on the test setup, use the same frequency for generating snapshots on a production machine.
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When you change the frequency of snapshot generation, it affects the snapshot generation that occurs after this change. Any snapshots that are created prior to the frequency change are not affected. If there are pre-existing snapshots prior to frequency change, the system does not generate the missing snapshots matching the new frequency.
For example, consider an item with 5400 edits where 5 snapshots were created using a frequency of 1000. Note the generation of snapshots in the following cases:
• Case 1: Frequency changed to 1500
If the administrator changes the frequency to 1500, the next snapshot is generated at the 6000th edit as 6000 is a multiple of 1500. The snapshot that follows is generated at 7500th edit which is the next multiple of the 1500.
• Case 2: Frequency changed to 500
If the administrator changes the frequency to 500, the next snapshot is generated at the 5500th edit as it is the next multiple of 500. The snapshot that follows is generated at the 6000th edit as it is the next multiple of 500.
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Changing the snapshot generation frequency does not delete existing snapshots.
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Generate snapshots forcefully
You can use diagnostic commands to generate the snapshot at the edit nearest to a specific date, or regenerate the snapshots for an item.
The command usage is as follows:
diag --diag=generatesnapshot --param=itemid=<itemid> [--param=regenerate] [--param=date=<edit-date>]
For example:
• To generate all snapshots with the frequency set in the property, the command is:
diag --diag=generatesnapshot --param=itemid=<itemid> --param=regenerate
• To generate snapshots at the edit closest to a date, the command is:
diag --diag=generatesnapshot --param=date='<edit-date>
