Table rotation

Table rotation preserves instance performance and averts risk associated with querying growing data sets by using the External Communication Channel (ECC) Queue and the sys_created_on field to separate data sets into multiple tables based on date.

Functionality
The administrator specifies the time parameter (duration) of the process and the number of tables (rotations) within. After the rotation writes the last table in a rotation, the rotation overwrites the first table in the rotation. Please contact ServiceNow Technical Support before applying table rotation to a custom table.
Examples:
  • The query Records created between 2015/12/10 08:49 and 2015/12/09 07/34 where topic=SystemCommand is translated to a SQL query on a single table, because the clause on sys_created_on targets a single shard.
  • The query Records updated between 2015/12/10 08:49 and 2015/12/09 07/34 where topic=SystemCommand, or without a date range, needs to target all shards and therefore is translated as a union query on all shards.
Advantages
  • Allows deletion of old data without affecting current data (for example, to drop or truncate a table).
  • Ensures tables only grow to a reasonable size.
  • Reduces working set of data when date is known for query.
Disadvantages
Queries that do not use the table rotation date (for example, by using the sys_created_on field), force an inefficient union query to query time ranges that span multiple tables and can be extremely slow if the number of sub-tables is large.

To improve performance, it is recommended that the query includes a window of created dates.

You can use table rotation for sequentially-written tables or for insert-only tables. You cannot use table rotation for sys_import tables or tables that extend the Task [task] table.