OpenIDM Integrator's Guide
10.9. Reconciliation Optimization

To optimize a reconciliation operation, the reconciliation process does not attempt to correlate source objects to target objects if the set of target objects is empty when the correlation is started. This considerably speeds up the process the first time the reconciliation is run. You can change this behavior for a specific mapping by adding the correlateEmptyTargetSet property to the mapping definition and setting it to true. For example:

{
    "mappings": [
        {
            "name"                     : "systemMyLDAPAccounts_managedUser",
            "source"                   : "system/MyLDAP/account",
            "target"                   : "managed/user",
            "correlateEmptyTargetSet"  : true
        },
    ]
}

Be aware that this setting will have a performance impact on the reconciliation process.