IPA replication failed with errors "Unable to acquire replica: error: replica busy locked"

Issue

• IPA replication not working properly.

Errors seen in /var/log/dirsrv/slapd-example/errors

[03/Oct/2012:02:37:17 +1300] NSMMReplicationPlugin - conn=1147 op=155581 replica="dc=example,dc=com": Unable to acquire replica: error: replica busy locked by conn=838 id=11 for incremental update

This can also be seen in the output of ipa-replica-manage list -v command (in IDM environment):

idm.example.com: replica
  last init status: 0 Total update succeeded
  last init ended: 2018-06-08 03:01:25+00:00
  last update status: Error (1) Can't acquire busy replica
  last update ended: 1970-01-01 00:00:00+00:00

Note: in newer versions, this message could be slightly different:

last update status: Error (18) Replication error acquiring replica: Incremental update transient error.  Backing off, will retry update later. (transient error)