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Symptoms


Altering/creating tables extended from CMDB is updating millions of rows for all records on all CMDB-extended tables.

Release


Jakarta+

 

Cause


  1. The CMDB table uses an extension model called table-per-partition (TPP).
  2. TPP stores all extended tables on a flat set of database tables called partitions.
  3. Since all tables are stored as one single-flattened partition, changing one column on one extended table has to alter all rows at the database level.
  4. This process is performed via an "online alter".
    • This allows the alter to take place on a temporary table to avoid locking the entire CMDB hierarchy during the process.
    • Although the CMDB table is not entirely locked, this process is still very time consuming.

Resolution


  • This is expected platform behavior.
  • Although this is allowed, it is important to understand the extension models used by ServiceNow before performing database schema changes.

 

Additional Information


Documentation topic: Table flattening

Article Information

Last Updated:2018-06-04 07:12:06
Published:2018-06-04