Progress Fathom Replication
User’s Guide

> ## Schema lock

> Whenever the schema is changed on the source database, a schema lock is required. The Fathom Replication server communicates a schema lock request to the Fathom Replication agent causing a schema lock on the target database as well. The Fathom Replication agent will write a message to the target database log indicating that there is a schema lock requested.

> By default, this lock will be held until the schema changes are completed on both the source and target database. If a user in read-only mode on the target database is accessing tables, the schema lock cannot occur until the user releases the tables. The user process requesting the schema lock will block until it gets the schema lock. The DBA must ensure that users on the read-only target database do not prevent a client on the source database from making a schema change.

> Alternatively, you can set the Schema-Lock-Action server property to Force. The agent will attempt to acquire the exclusive schema lock five times. If the fifth attempt fails, the agent disconnects all users from the target and makes another attempt. If the last attempt fails, the server and all agents terminate. This allows the source database to resume normal activity. When schema update activity completes, the server and target can be restarted.

> For more information, see the "Fathom Replication properties" section.

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