Starting slapd service failed with "backend_startup_one: bi_db_open failed! (12)" error

Issue

• Starting slapd service throws following error

  # service ldap start 
  Checking configuration files for slapd:  bdb_db_open: DB_CONFIG for suffix dc=compass,dc=cnsonline,dc=net has changed. 
  Performing database recovery to activate new settings. 
  bdb_db_open: Recovery skipped in read-only mode. Run manual recovery if errors are encountered. 
  bdb(dc=compass,dc=cnsonline,dc=net): Lock table is out of available locker entries 
  bdb_db_open: db_open(/var/lib/ldap/id2entry.bdb) failed: Cannot allocate memory (12) 
  bdb(dc=compass,dc=cnsonline,dc=net): Unknown locker ID: 18bb 
  bdb(dc=compass,dc=cnsonline,dc=net): Unknown locker ID: 0 
  backend_startup_one: bi_db_open failed! (12) 
  slap_startup failed (test would succeed using the -u switch) 
                                                             [FAILED] 
  stale lock files may be present in /var/lib/ldap           [WARNING]