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mongodbshardingdatabase-backupsdatabase-administration
Lucia Pasarin
Lucia Pasarin

Reputation: 2308

MongoDB. Keep information about sharded collections when restoring

I am using mongodump and mongorestore in a replicated shard cluster in MongoDB 2.2. to get a backup and restore it.

First, I use mongodump for creating the dump of all the system, then I drop a concrete collection and restore it using mongorestore with the output of mongodump. After that, the collection is correct (the data it contains is correct and also the indexes), but the information about if this collection is sharded is lost. Before dropping it, the collection was sharded. After the restore, however, the collection was not sharded anymore.

I was wondering then if a way of keeping this information in backups exist. I was thinking that maybe sharded information for collection is kept in the admin database, but in the dump, admin folder is empty, and using show collections for this database I get nothing. Then I thought it could be kept in the metadata, but this would be strange, because I know that, in the metadata, the information about indexes is stored and indexes are correctly restored.

Then, I would like to know if it could be possible to keep this information using instead of mongodump + mongorestore, filesystem snapshots; or maybe still using mongodump and mongorestore but stopping the system or locking writing. I don't thing this last option could be the reason, because I am not performing writing operations while restoring even not being locking it, but just to give ideas.

I also would like to know if anyone is completely sure about if it is the case that this feature is still not available in the current version.

Any ideas?

Upvotes: 0

Views: 1098

Answers (1)

Asya Kamsky
Asya Kamsky

Reputation: 42352

If you are using mongodump to back up your sharded collection, are you sure it really needs to be sharded? Usually sharded collections are very large and mongodump would take too long to back it up.

What you can do to back up a large sharded collection is described here.

The key piece is to back up your config server as well as each shard - and do it as close to "simultaneously" as possible after having stopped balancing. Config DB is small so you should probably back it up very frequently anyway. Best way to back up large shards is via file snapshots.

Upvotes: 1

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