Blog Post

Marking FK Constraints NOT FOR REPLICATION

,

When administering Merge Replication, sometimes we need to mark foreign

key constraints NOT FOR REPLICATION.  In some cases, we might require

replication agent activity to be treated differently from user activity

since we cannot guarantee the order of changes that are replicated.  To

be more specific, sometimes parent and child records are sent in

different batches, with the children getting sent first, resulting in

constraint violations and conflicts.

There are a few scenarios that cause this behavior to occur and some of the details are covered in the following links.

By marking foreign key constraints NOT FOR REPLICATION, we can alleviate constraint violations from occurring when changes are made by replication agents.  With that said, it takes a fair amount of faith to trust that Merge will in fact deliver the parent records in the next batch of changes.  That's why it's wise to take a closer look when this happens and verify that after dropping and adding the constraints NOT FOR REPLICATION, that the parent records do arrive.

Dropping and adding foreign key constraints NOT FOR REPLICATION can be time consuming if there are a large number of them.  To speed this process up, I've been using variations of the following SELECT to generate my ALTER statements:

USE AdventureWorks;
GO
SELECT
  Drop_FK = 'ALTER TABLE [' + FK.FKTableSchema +
    '].[' + FK.FKTableName + '] DROP CONSTRAINT [' + FK.FKName + ']; ',
  Add_FK_NFR = 'ALTER TABLE [' + FK.FKTableSchema +
    '].[' + FK.FKTableName +
    '] WITH CHECK ADD CONSTRAINT [' + FK.FKName +
    '] FOREIGN KEY([' + FK.FKTableColumn +
    ']) REFERENCES [' + schema_name(sys.objects.schema_id) +
    '].[' + sys.objects.[name] + ']([' + sys.columns.[name] +
    ']) NOT FOR REPLICATION; '
FROM sys.objects
INNER JOIN sys.columns
  ON (sys.columns.[object_id] = sys.objects.[object_id])
INNER JOIN (
  SELECT
    sys.foreign_keys.[name] AS FKName,
    schema_name(sys.objects.schema_id) AS FKTableSchema,
    sys.objects.[name] AS FKTableName,
    sys.columns.[name] AS FKTableColumn,
    sys.foreign_keys.referenced_object_id AS referenced_object_id,
    sys.foreign_key_columns.referenced_column_id AS referenced_column_id
  FROM sys.foreign_keys
  INNER JOIN sys.foreign_key_columns
    ON (sys.foreign_key_columns.constraint_object_id = sys.foreign_keys.[object_id])
  INNER JOIN sys.objects
    ON (sys.objects.[object_id] = sys.foreign_keys.parent_object_id)
  INNER JOIN sys.columns
    ON (sys.columns.[object_id] = sys.objects.[object_id])
      AND (sys.columns.column_id = sys.foreign_key_columns.parent_column_id)
) FK
  ON (FK.referenced_object_id = sys.objects.[object_id])
    AND (FK.referenced_column_id = sys.columns.column_id)
WHERE (sys.objects.[type] = 'U')
  AND (sys.objects.is_ms_shipped = 0)
  AND (sys.objects.[name] NOT IN ('sysdiagrams'))

 

This has been tested on SQL Server 2008 R2 against the AdventureWorks database.  It does not handle composite foreign keys, among other things, but should provide a good starting point.  If you have any questions, feel free to get in touch.


Rate

★ ★ ★ ★ ★ ★ ★ ★ ★ ★

You rated this post out of 5. Change rating

Share

Share

Rate

★ ★ ★ ★ ★ ★ ★ ★ ★ ★

You rated this post out of 5. Change rating

Related content

Technical Article

Database Mirroring FAQ: Can a 2008 SQL instance be used as the witness for a 2005 database mirroring setup?

Question: Can a 2008 SQL instance be used as the witness for a 2005 database mirroring setup? This question was sent to me via email. My reply follows. Can a 2008 SQL instance be used as the witness for a 2005 database mirroring setup? Databases to be mirrored are currently running on 2005 SQL instances but will be upgraded to 2008 SQL in the near future.

★ ★ ★ ★ ★ ★ ★ ★ ★ ★

You rated this post out of 5. Change rating

2009-02-23

1,567 reads

Technical Article

Networking - Part 4

You may want to read Part 1 , Part 2 , and Part 3 before continuing. This time around I'd like to talk about social networking. We'll start with social networking. Facebook, MySpace, and Twitter are all good examples of using technology to let...

★ ★ ★ ★ ★ ★ ★ ★ ★ ★

You rated this post out of 5. Change rating

2009-02-17

1,530 reads

Technical Article

Speaking at Community Events - More Thoughts

Last week I posted Speaking at Community Events - Time to Raise the Bar?, a first cut at talking about to what degree we should require experience for speakers at events like SQLSaturday as well as when it might be appropriate to add additional focus/limitations on the presentations that are accepted. I've got a few more thoughts on the topic this week, and I look forward to your comments.

★ ★ ★ ★ ★ ★ ★ ★ ★ ★

You rated this post out of 5. Change rating

2009-02-13

360 reads