Logger tables: TTL

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Hi All,

Within the DM docs regarding logger tables (Implementing logger tables | DataMiner Docs), it is first stated that a column with ColumnDefinition DATETIME should be added in order to define the TTL via the Partition tag.

My first questions are:

  • If within a logger table, we have only one column with such Partition option, the TTL will apply to all columns of the logger table, right?
  • Is it allowed to have the Partition tag on multiple columns of the same Logger table? (I would guess not as I don't quite see what would be the use of it but would like to be sure so we can make the DM Docs more explicit about it). If it is allowed, what will then be used for columns which don't have any TTL defined?

Then, later on in the doc, we have the following:

  • Does this mean that we don't need any DATETIME column anymore at all and can simply use any of the column in order to define the TTL for the whole logger table?
  • Or does it mean that, on top of the DATETIME column, we can add Partition tags to other columns in order to have a different TTL for different columns?
Simon Vandamme [SLC] [DevOps Advocate] Selected answer as best 12th January 2023
Alex Silva [DevOps Member] commented

My interpretataion of the docs points towards your second option “on top of the DATETIME column, we can add Partition tags to other columns in order to have a different TTL”.
Waiting forward to see the experts answer.

1 Answer

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Hi all,

I was now able to find answers to my above questions:

  • defining TTL (via the Partition tag) on more than one column for the same logger table will not work and we (Skyliners) are currently not aware of any use-case that would require this.
  • when defining the TTL (via the Partition tag) on a column, the TTL setting applies to all columns of the given logger table.
  • only for MySql (soon to be obsolete) logger tables, the TTL should be defined on a DATETIME column.
  • for Cassandra & Elastic logger tables, a DATETIME column is not required at all and the TTL can be defined on any randomly chosen column of the logger table (we would then typically add it to the Primary Key column)

I will follow up on making sure the DM Docs get updated to make all of this more explicit & clear.

Simon Vandamme [SLC] [DevOps Advocate] Edited answer 12th January 2023