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Excluding a Replica from a Replica Set

You can temporarily exclude a replica from its replica set when the clearinghouse in which the replica is stored unexpectedly becomes unavailable. This makes it possible for CDS to complete skulks of the directory during the time the excluded replica is unavailable.

To exclude a replica from a replica set, you use the dcecp directory modify command with the exclude argument to rebuild a directory's replica set, excluding the replica that you specify. Remember that you must account for all existing replicas in the command.

In the following example, the replica set of the /.:/eng directory consists of three replicas: the master replica, which is stored in clearinghouse /.:/Chicago1_CH, and the read-only replicas that are stored in clearinghouses /.:/NY1_CH and /.:/NY2_CH.

In this case, the /.:/NY1_CH clearinghouse is cut off from the network because of accidental damage to the network transmission lines. Connectivity to the clearinghouse will not be restored for several days. During this period, skulks of the /.:/eng directory will fail unless you temporarily exclude the read-only replica that is stored in clearinghouse /.:/NY1_CH.

To make it possible for skulks of the /.:/eng directory to succeed during the repair period, enter the following command to overwrite the current values of the /.:/eng directory's CDS_Replicas attribute with new values that include only the replicas that are stored in the /.:/NY2_CH and /.:/Chicago1_CH clearinghouses:

dcecp> directory modify/.:/eng -master /.:/Chicago1_CH \
> -readonly /.:/NY2_CH exclude /.:/NY1_CH
dcecp>

The following figure shows the result of the preceding command.


Example Replica Set After Replica Exclusion

When connectivity with the /.:/NY1_CH clearinghouse is reestablished, enter the following command to reintroduce the read-only replica that is stored in clearinghouse /.:/NY1_CH to the replica set:

dcecp> directory modify/.:/eng -master /.:/Chicago1_CH \ > -readonly {/.:/NY1_CH /.:/NY2_CH}
dcecp>

Note: Always reintroduce excluded replicas to their replica sets as soon as possible after the clearinghouse in which they reside again becomes available.