Mongo

Commands

  • mongo ${DB} - connect to db
  • show dbs - show databases
  • show tables|collections - show tables or collections
  • use ${DB} - connect to ${DB}
  • db.collections.findOne({"A":"B"}) or db.collections.find({"A":"B"}).pretty() - find one record from collections
  • rs.slaveOk() - allow queries from SECONDARY node
  • mongodump --host IPADDRESS --port PORT --db DB --collection=COLLECTION --out=/var/backup/ - backup COLLECTION from DB
  • db.collection.creaateIndex( keys, { background: true } ); - create indexes in background to avoid mongo to lock all other operations

Administration

Promote new primary in replica set

Restrict 3rd box to become primary and set priority to 0 to avoid elections on it.After cfg update promote specific slave to become new master.

# on primary
cfg = rs.conf()
cfg.members[2].priority = 0
rs.reconfig(cfg)
rs.stepDown()

Later, on new master set revert priority to its default value.

# on new primary
cfg = rs.conf()
cfg.members[2].priority = 1
rs.reconfig(cfg)