MongoDB Replica Set Oplog Resize Helper Script

resize-mongodb-oplog.sh

#!/bin/sh

function usage() {
  echo
  echo "Resizing the local MongoDB RS Oplog"
  echo
  echo "Usage:"
  echo "mongodb_resize_oplog <mongodb local port> <mongodb data path> <new oplog size in gb> <user:group for data dir>"
  echo
  echo "Example:"
  echo "resize-mongodb-oplog.sh 27017 /mongodb/data 8 mongodb:users"
}

ask() {
	echo "Continue? (y/n)"
	read i
	if [ "$i" != "y" ]
	then
		echo "Aborting, remember to clean up the steps we already did."		
		exit 1
	fi
}

resizeOplog() {
	MONGO_INSTANCE_PORT=$1
	MONGO_DATA_PATH=$2
	MONGO_OPLOG_SIZE=$3
	MONGO_USER_GROUP=$4

	echo "1. Step down node"
	ask
	echo "rs.stepDown()" | mongo localhost:${MONGO_INSTANCE_PORT}

	echo "2. Shutdown down node"
	ask
	echo "use admin
db.shutdownServer()" | mongo localhost:${MONGO_INSTANCE_PORT}
	sleep 2

	echo "3. Restart in local mode"
	ask
	mongod --port 37017 --dbpath ${MONGO_DATA_PATH} --directoryperdb --fork --logpath /tmp/mongo.log

	echo "4. Dump oplog.rs"
	ask
	mongodump --db local --collection 'oplog.rs' --port 37017

	echo "5. Save last seed of oplog.rs in temp"
	ask
	echo "use local
db = db.getSiblingDB('local')
db.temp.drop()
db.temp.save( db.oplog.rs.find( { }, { ts: 1, h: 1 } ).sort( {\$natural : -1} ).limit(1).next() )
db.temp.find()" | mongo localhost:37017

	echo "6. Drop current oplog.rs"
	ask
	echo "use local
db = db.getSiblingDB('local')
db.oplog.rs.drop()" | mongo localhost:37017

	echo "6. Create new empty oplog.rs with ${MONGO_OPLOG_SIZE} GB"
	ask
	echo "use local
db = db.getSiblingDB('local')
db.runCommand( { create: 'oplog.rs', capped: true, size: (${MONGO_OPLOG_SIZE} * 1024 * 1024 * 1024) } )" | mongo localhost:37017

	echo "7. Restore saved seed in new oplog.rs"
	ask
	echo "use local
db = db.getSiblingDB('local')
db.oplog.rs.save( db.temp.findOne() )
db.temp.drop()
db.oplog.rs.find()" | mongo localhost:37017

	echo "8. Shutdown local mode"
	ask
	echo "use admin
db.shutdownServer()" | mongo localhost:37017
	sleep 2
	
	chown -R ${MONGO_USER_GROUP} /mongoDB/node/data

	echo "9. Start in normal RS mode"
	ask
	/etc/init.d/mongod start

	echo "Finished resize of oplog.rs, please verify and remove logfile /tmp/mongo.log and dumps of old oplog.rs in working directory"
}

if [ "$#" == 4 ]; then
  resizeOplog $1 $2 $3 $4
else 
  usage
  exit 1
fi