For development reasons, I need to backup a production replica set mongodb and restore it on a stand alone, different machine test instance.
Some docs are talking about the opposite ( standalone 2 replica-set ), but I cannot find his downgrade/rollback way.
What's the way to go, in this case ?
No matter how many nodes you have in a replica set, each of them holds the same data.
So getting the data is easy - just use mongodump (preferably against the secondary, for performance reasons) and then mongorestore into a new mongod for your development stand-alone system.
mongodump does not pick up any replication related collections (they live in database called local). If you end up taking a file system snapshot of a replica node rather than using mongodump, be sure to drop the local database when you restore the snapshot into your production stand-alone server and then restart mongod so that it will properly detect that it is not part of a replica set.
Related
We are using mongodb cluster with set of 3 members , and all consumers are able to read/write data.
Use mongo.conf file to create cluster && configure replica set, which are executed in ansible script as part of system restart.
Our system does heavy writes/read operation on mongo clusters ,and sometime replica get broken.
Then it is no longer feasible to restore replica without deleting data from one of the corrupted server.
Here are my queries:
what is better way to notify when replica is broken using script/some code?We can not use Mongo atlas
etc.
What is efficient way to restore data on corrupted member.
What is better way to notify when replica is broken using script/some code?
Use the replSetGetStatus database command.
You can run this command from any driver or the shell. Among other things, it returns the state (primary/secondary/startup/recovery/unreachable) and last applied operation time for each member.
What is efficient way to restore data on corrupted member.
Check out the docs for a few options: https://docs.mongodb.com/manual/tutorial/resync-replica-set-member/#resync-a-member-of-a-replica-set
Postgres and the default location for its storage is at my C-drive. I would like to restore a backup to another database but to access it via the same Postgres server instance - the issue is that the size of the DB is too big to be restore on the same c-drive ...would it be possible to tell Postgres that the second database should be restore and placed on another location/drive (while still remaining the first one)? Like database1 at my C-drive and database2 at my D-drive?
Otherwise the second best solution would be to install 2 separate Postgres instances - but that also seems a bit overkill?
That should be entirely achievable, if you've used the postgres pg_dump command.
The pg_dump command does not create the database, so you create it yourself first. Use CREATE TABLESPACE to specify the location.
CREATE TABLESPACE secondspace LOCATION 'D:\postgresdata';
CREATE DATABASE seconddb TABLESPACE secondspace;
This creates an empty database on the D: drive.
Then the standard restore from a pg_dump should work:
psql seconddb < dumpfile
Replication
Sounds like you need database replication.
There are several ways to do this with Postgres, one built-in, and other approaches using add-on libraries.
Built-in replication feature
The built-in replication feature is likely to suit your needs. See the manual. In this approach, you have an instance of Postgres running on your primary server, doing reads and writes of your data. On a second server, an entirely separate computer, you run another instance of Postgres known as the replica. You first set up the replica by doing a full backup of your database on the first server, and restore to the second server.
Next you configure the replication feature. The replica needs to know it is playing the role of a replica rather than a regular database server. And the primary server needs to know the replica exists, so that every database change, every insert, modification, and deletion, can be communicated.
WAL
This communication happens via WAL files.
The Write-Ahead Log (WAL) feature in Postgres is where the database writes all changes first to the WAL, and only after that is complete, then writes to the actual database. In case of crash, power outage, or other failure, the database upon restarting can detect a transaction left incomplete. If incomplete, the transaction is rolled back, and the database server can try again by seeing the "To-Do" list of work listed in the WAL.
Every so often the current WAL is closed, with a new WAL file created to take over the work. With replication enabled, the closed WAL file is copied to the replica. The replica then incorporates that WAL file, to follow the same "To-Do" list of changes as written in that WAL file. So all changes are made to the replica database exactly as they were made to the primary database. Your replica is an exact match to the primary, except for a slight lag in time. The replica is always just one WAL file behind the progress of the primary.
In times of trouble, the replica serves as a warm stand-by. You can shutdown the primary, then tell the replica that it is now the primary. You can even configure the replica to be a hot stand-by, meaning it will automatically take-over when the primary seems to have failed. There are pros and cons to hot stand-by.
Offload read-only queries
As a bonus feature, the replica can be used for read-only queries. If your database is heavily used, you can offload some of the work burden from your primary to the replica. Any queries that do not require the absolute latest information can be shifted by connecting to the replica rather than the original. For example, a quarterly sales report likely does not need the latest data stored in the active WAL file that has not yet arrived on the replica.
Physical replication means all databases are copied
Caveat: This built-in replication feature is physical replication. This means all the changes to the entire Postgres installation (formally known as a cluster, not to be confused with a hardware cluster) is copied to the replica. If you use one Postgres server to server multiple databases, all those databases must be replicated – you cannot pick and choose which get copied over. There may be alternative replication features in the future related to logical replication.
More to learn
I am being brief here. The topics of replication, high-availability, and disaster-recovery are broad and complex, too much for an Answer on Stack Overflow.
Tip: This kind of Question might have been better asked on the sister site, DBA.StackExchange.com.
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.
There is a Replica set (primary, secondary, arbiter) with 300GB data. i want to make daily backup without lock. The Replica is placedWe use Windows 2008R2, so seems not possible to use lvm tools.
If i want to make folder copy on secondary, it needed to shut down mongod first (because its not possible copy mongod.lock while mongod is running).
What is the best solution to make fastest daily backup
I don't know if it is feasible for you, but you can add another member to replica set. This member would be hidden, so it would not be used for queries or writing operations. You can stop this server every day for make your database backups.
because it is a replicate cluster i use mongodump with the --oplog option. runs pretty quick on linux. and i think it may have some advantages in a multi tenant server over over tar or snap. disadvange is that the indexes are built when you do the mongorestore
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.