Directory Server Replication

Directory Server lets you replicate directory data for availability and load balancing between the servers in your deployment. Directory Server allows you to have multiple read-write (master) replicas deployed together.

Internally, the server makes this possible by keeping track of changes to directory data. When the same data are modified on more than one read-write replica Directory Server can resolve the changes correctly on all replicas. The data to track these changes, must be retained until they are no longer needed for replication. Changes are retained for a period of time specified by the purge delay whose default value is seven days. If your directory data undergoes much modification, especially of large multi-valued attributes, this data can grow quite large.

Because the level of growth is dependent on several factors, there is no catch-all formula to calculate potential data growth. The best approach is to test typical modifications and measure the growth. The following factors have an effect on data growth as a result of entry modification:

• The type of entries and the types of attributes that are modified.

  Multi-valued attributes cause larger growth. If the attribute values are small, the growth is more visible.

• The workload applied to the entry.

  Adding and deleting entries causes larger growth. Adding an attribute value causes larger growth than replacing an attribute value.

• The number of entries that are modified, and the number of attributes that are modified in each entry.

• The size of the database page.

  After numerous modifications, certain entries can become larger than the database page size.

Note that the replication metadata remains in the entry until the purge delay has passed and the entry is modified again.

For a detailed discussion of Directory Server replication, read Chapter 7, Directory Server Replication, in Sun Directory Server Enterprise Edition 7.0 Reference.