A protected read-only target is used to receive information from a full peer source. The term protected means that this target contains sufficient information to detect collisions against the source copy of the data. Users must not make changes to the data in a protected read-only target, although Ingres Replicator does not prevent this. The ability to detect and resolve collisions provides a protection against any change that is made to a replicated table from another source. Note that collisions resulting from updating data directly at the protected read-only target are generally not detectable.

A protected mode is important because more than one source can be transmitting to a single protected read-only target. If the target is not protected, transactions can arrive out of order. A protected read-only target maintains a shadow table for each replicated table but does not maintain archive tables or input and distribution queues. This allows the target to only accept replicated rows in order, thus ensuring that consistent data is available to users. Other sources replicate data to this target by database procedures; so although this target does not send data, all replicated tables in the protected read-only target must be registered with Ingres Replicator, and most Ingres Replicator support objects must be present.