I started a mongo dump and my database is with 95% of storage filled, and I am downloading to my local machine the bson file.
But it is very slow and I am afraid to stop mongo dump to increase server storage size, and one observation I am downloading a database to change to mongo atlas because I think it is easier to administrate.
Is there any command to stop mongodump safely?
mongodump is a process that dump the data from your DB, it is not supposed to be stopped after performing some operations rather than others, but even stopping it not safely (e.g. sending an interrupt signal):
Your DB will just release the read lock for mongodump
The worst that could happen on your machine is having a malformed BSON
Related
Is it safe to run mongodump against running server with many writes per second? Is it possible to get corrupted dump doing in this way?
From here:
Use --oplog to capture incoming write operations during the mongodump operation to ensure that the backups reflect a consistent data state.
Does it mean that no matter how many writes in database dump will be consistent?
If I ran mongodump --oplog at 1AM and it finished at 2AM then I run mongorestore --oplogReplay what state will I get?
From here:
However, the use of mongodump and mongorestore as a backup strategy can be problematic for sharded clusters and replica sets.
but why? I had replica set of 1 primary and 2 secondary. What the problem to run mongodump against one of secondary? It should same as primary (except replication lag difference).
The docs are quite clear about it:
--oplog
Creates a file named oplog.bson as part of the mongodump output. The oplog.bson file, located in the top level of the output directory, contains oplog entries that occur during the mongodump operation. This file provides an effective point-in-time snapshot of the state of a mongod instance. To restore to a specific point-in-time backup, use the output created with this option in conjunction with mongorestore --oplogReplay.
Without --oplog, if there are write operations during the dump operation, the dump will not reflect a single moment in time. Changes made to the database during the update process can affect the output of the backup.
--oplog has no effect when running mongodump against a mongos instance to dump the entire contents of a sharded cluster. However, you can use --oplog to dump individual shards.
Without --oplog you still get a valid dump, just a bit inconsistent - some of the writes done between 1 AM and 2 AM will be missing.
With --oplog you have the oplog file captured at 2 AM. The dump remains inconsistent, and replaying the oplog on restore fixes this issue.
The problems dumping the sharded clusters deserve a dedicated page in the docs. Essentially because of complexity to synchronise backups of all nodes:
To create backups of a sharded cluster, you will stop the cluster balancer, take a backup of the config database, and then take backups of each shard in the cluster using mongodump to capture the backup data. To capture a more exact moment-in-time snapshot of the system, you will need to stop all application writes before taking the filesystem snapshots; otherwise the snapshot will only approximate a moment in time.
There are no problems to dump replica set.
I have a fairly small MongoDB instance (15GB) running on my local machine, but I need to push it to a remote server in order for my partner to work on it. The problem is twofold,
The server only has 30GB of free space
My local internet connection is very unstable
I tried copyDatabase to transfer it directly, but it would take approximately 2 straight days to finish, in which the connection is almost guaranteed to fail at some point. I have also tried both mongoexport and mongodump but both produce files that are ~40GB, which won't fit on the server, and that's ignoring the difficulties of transferring 40GB in the first place.
Is there another, more stable method that I am unaware of?
Since your mongodump output is much larger than your data, I'm assuming you are using MongoDB 3.0+ with the WiredTiger storage engine and your data is compressed but your mongodump output is not.
As at MongoDB 3.2, the mongodump and mongorestore tools now have support for compression (see: Archiving and Compression in MongoDB Tools). Compression is not used by default.
For your use case as described I'd suggest:
Use mongodump --gzip to create a dump directory with compressed backups of all of your collections.
Use rsync --partial SRC .... DEST or similar for a (resumable) file transfer over your unstable internet connection.
NOTE: There may be some directories you can tell rsync to ignore with --exclude; for example the local and test databases can probably be skipped. Alternatively, you may want to specify a database to backup with mongodump --gzip --db dbname.
Your partner can use a similar rsync commandline to transfer to their environment, and a command line like mongorestore --gzip /path/to/backup to populate their local MongoDB instance.
If you are going to transfer dumps on an ongoing basis, you will probably find rsync's --checksum option useful to include. Normally rsync transfers "updated" files based on a quick comparison of file size and modification time. A checksum involves more computation but would allow skipping collections that have identical data to previous backups (aside from the modification time).
If you need to sync data changes on ongoing basis, you also may be better moving your database to a cloud service (eg. a Database-as-a-Service provider like MongoDB Atlas or your own MongoDB instance).
We have a three-server replicaset running MongoDB 2.2 on Ubuntu 10.04, and recently had to upgrade the hard drive for each server where one particular database resides. This database contains log information for web service requests, where they write to collections in hourly buckets using the current timestamp to determine the name, e.g. log_yyyymmddhh.
I performed this process:
backup the database on the primary server with mongodump --db log_db
take a secondary server offline, replace the disk
bring the secondary server up in standalone mode (i.e. comment out the replSet entry
in /etc/mongodb.conf before starting the service)
restore the database on the secondary server with mongorestore --drop --db log_db
add the secondary server back into the replicaset and bring it online,
letting replication catch up the hourly buckets that were updated/created
while it had been offline
Everything seemed to go as expected, except that the collection which was the current bucket at the time of the backup was not brought up to date by replication. I had to manually copy that collection over by hand to get it up to date. Note that collections which were created after the backup were synched just fine.
What did I miss in this process that caused MongoDB not to get things back in synch for that one collection? I assume something got out of whack with regard to the oplog?
Edit 1:
The oplog on the primary showed that its earliest timestamp went back a couple of days, so there should have been plenty of space to maintain transactions for a few hours (which was the time the secondary was offline).
Edit 2:
Our MongoDB installation uses two disk partitions: /dev/sda1 and /dev/sdb1. The primary MongoDB directory /var/lib/mongodb/ is on /dev/sda1, and holds several databases, while the log database resides by itself on /dev/sdb1. There's a sym link /var/lib/mongodb/log_db which points to a directory on /dev/sdb1. Since the log db was getting full, we needed to upgrade the disk for /dev/sdb1.
You should be using mongodump with the --oplog option. Running a full database backup with mongodump on a replicaset that is updating collections at the same time may not leave you with a consistent backup. This becomes worse with larger databases, more collections and more frequent updates/inserts/deletes.
From the documentation for your version (2.2) of MongoDB (it's the same for 2.6 but just to be as accurate as possible):
--oplog
Use this option to ensure that mongodump creates a dump of the
database that includes an oplog, to create a point-in-time snapshot of
the state of a mongod instance. To restore to a specific point-in-time
backup, use the output created with this option in conjunction with
mongorestore --oplogReplay.
Without --oplog, if there are write operations during the dump
operation, the dump will not reflect a single moment in time. Changes
made to the database during the update process can affect the output
of the backup.
http://docs.mongodb.org/v2.2/reference/mongodump/
This is not covered well in most MongoDB tutorials around backups and restores. Generally you are better off if you can perform a live snapshot of the storage volume your database resides on (assuming your storage solution has a live snapshot ability compatible with MongoDB). Failing that, your next best bet is taking a secondary offline and then performing a snapshot or backup of the database files. Mongodump on a live database is increasingly a less optimal solution for larger databases due to performance issues.
I'd definitely take a look at the MongoDB overview of backup options: http://docs.mongodb.org/manual/core/backups/
I would guess this has to do with the oplog not being long enough, although it seems like you checked that and it looked reasonably big.
Still, when adding new members to a replica set you shouldn't be snapshotting and restoring them. It's better to simply add a new member and let replication happen by itself. This is described in the Mongo docs and is the process I've always followed.
I'm looking for the right way to do a Mongodb backup on a replica set (non-sharded).
By reading the Mongodb documentation, I understand that a "mongodump --oplog" should be enough, even on a replica (slave) server.
From the mongodb / mongodump documentation :
--oplog
Use this option to ensure that mongodump creates a dump of the database that includes an oplog, to create a point-in-time snapshot of the state of a mongod instance. To restore to a specific point-in-time backup, use the output created with this option in conjunction with mongorestore --oplogReplay.
Without --oplog, if there are write operations during the dump operation, the dump will not reflect a single moment in time. Changes made to the database during the update process can affect the output of the backup
I'm still having a very hard time to understand how Mongodb can backup and keep writing on the database and make a consistent backup, even with --oplog.
Should I lock my collections first or is it safe to run "mongodump --oplog ?
Is there anything else I should know about?
Thanks.
The following document explains how mongodump with –oplog option works to create a point in time backup.
http://docs.mongodb.org/manual/tutorial/backup-databases-with-binary-database-dumps/
However, using mongodump and mongorestore to back up and restore MongodDB can be slow. If file system snapshot is an option, you may want to consider using snapshot for MongoDB backup. Information from the following link details two snapshot options for performing hot backup of MongoDB.
http://docs.mongodb.org/manual/tutorial/backup-databases-with-filesystem-snapshots/
You can also look into MongoDB backup service.
http://www.10gen.com/products/mongodb-backup-service
I'm in the middle of setting up a backup strategy for mongo, was just curious to know if mongodump locks the database before performing the database dump?
I found this on mongo's google group:
Mongodump does a simple query on the live system and does not require
a shutdown. Like all queries it requires a read lock while running but
doesn't not block any more than normal queries.
If you have a replica set you will probably want to use the --oplog
flag to do your backups.
See the docs for more information
http://docs.mongodb.org/manual/administration/backups/
Additionally I found this previously asked question
MongoDB: mongodump/restore vs. backup up files directly
Excerpt from above question
Locking and copying files is only an option when you don't have heavy
write load.
mongodump can be run against live server. It will create some
additional load, so don't do it on peak hours. Also, it is advised to
do it on a secondary node (if you don't use replica sets, you should).
There are some complications when you have a DB so large that no
single machine can hold it. See this document.
Also, if you have replica set, you take down one of secondaries and copy its files directly. See http://www.mongodb.org/display/DOCS/Backups:
Mongdump does not lock the db. It means other read and write operations will continue normally.
Actually, both mongodump and mongorestore are non-blocking. So if you want to mongodump mongorestore a db then its your responsibility to make sure that it is really a desired snapshot backup/restore. To do this, you must stop all other write operations while taking/restoring backups with mongodump/mongorestore. If you are running a sharded environment then its recommended you stop the balancer also.