How collisions occur and how to avoid them

A collision is an update that has a newer local update.

The platform detects collisions by comparing the values in the Name and Updated fields of the Customer Update record from each update set. If the name matches but there are different update date values, then there is a collision.

When a customer update is moved from one instance to another, it may be re-written to match the target instance. The re-write can involve changing the update name of the customer update and one or more sys_ids within the update. The re-writes are done when the record or the reference field is for a table that uses a coalesce strategy. This ensures that the customer update will be applied to the correct record. For example, if the sys_dictionary record for tablename.fieldname has sys_id 123456789 on instance A and sys_id 987654321 on instance B, when a customer update that refers to that record is retrieved from instance A and recorded in the sys_update_xml table on instance B, references to 123456789 are updated to read 987654321.

Coalesce Strategies

Update sets can detect collisions between identical records that you independently create on separate instances. To detect such collisions, the record must have a coalesce strategy based on coalescing columns. Because collision detection depends on uniqueness of tables, the tables must be unique when the coalescing columns are combined. Records that are not listed here will not collide if the same record is created separately on different instances.

Type Coalescing Columns
sys_db_object name
sys_dictionary name, element
sys_choice_set name, element, language
sys_documentation name, element, language
sys_properties name
sys_report_chart_color name, element, value
sys_ui_form name, view, sys_domain
sys_ui_message documentkey, language
sys_ui_list name, view, sys_domain, element, relationship, parent
sys_ui_section name, view, caption, sys_domain
sys_ui_related_list name, view, related_list, sys_domain
sys_ui_view name
sys_user_role name
sys_wizard name

How Customer Update record names affect collisions

To understand coalescing, it helps to understand how records that do not coalesce work:

For most record types, when a Customer Update is moved to a new instance, the system does not detect collisions for the following reason:

When you create a record, it receives a unique Sys ID. For most record types, the Sys ID becomes part of the Customer Update record name. For example:

sysevent_email_template_9e1998c078b71100a92ecacd80df1d39

Creating an identical record in the same table on another instance produces a Customer Update record name with a different Sys ID, for example:

sysevent_email_template_10b958c8653311005840134572f8e020

As a result, even though the records might be otherwise identical, the records have different names so the system does not detect the collision.

Coalescing records, in contrast, use the following approach to naming records and determining collisions: The following Customer Update record types use some or all of their coalescing columns instead of the Sys ID in their names. The resulting identical record name in each instance helps the system to identify collisions even if the records have different Sys IDs.

sys_dictionary

sys_documentation

sys_choice_set

sys_ui_list

sys_ui_related_list

To prevent creating duplicate records with update sets:

  • Transfer data with update sets rather than recreating it on separate instances to ensure the records have the same Sys ID.
  • Export and import records as XML files to ensure the records have the same Sys ID. See Export and import XML files.
  • Enable a unique index for the table from the system dictionary. See Table administration.
Note: The default records included in the baseline system will always have the same Sys ID because the instance imports the records as XML files during instance provisioning.