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i am trying to dump a mongodb collection to file, and then use that to restore to another mongodb instance.

dumping - 

mongodump --host 127.0.0.1 --port 27017 --username vespauser --password <passwd> --collection vespastats --db vespa --out /archive/vespa-archive/vespa-db-backup_001

    connected to: 127.0.0.1:27017
    2015-04-21T16:24:07.070-0400 DATABASE: vespa      to     /archive/vespa-archive/vespa-db-backup_testing01/vespa
    2015-04-21T16:24:07.141-0400    vespa.system.indexes to /archive/vespa-archive/vespa-db-backup_testing01/vespa/system.indexes.bson
    2015-04-21T16:24:07.148-0400             4 documents
    2015-04-21T16:24:07.149-0400    vespa.vespastats to /archive/vespa-archive/vespa-db-backup_testing01/vespa/vespastats.bson
    2015-04-21T16:24:07.316-0400             59724 documents
    2015-04-21T16:24:08.118-0400    Metadata for vespa.vespastats to /archive/vespa-archive/vespa-db-backup_testing01/vespa/vespastats.metadata.json

restoring - 

mongorestore -v --drop --host 127.0.0.1 --port 27017 --username admin --password <passwd> /archive/vespa-archive/vespa-db-backup_001

2015-04-21T16:31:11.962-0400 creating new connection to:127.0.0.1:27017
2015-04-21T16:31:11.963-0400 [ConnectBG] BackgroundJob starting: ConnectBG
2015-04-21T16:31:11.963-0400 connected to server 127.0.0.1:27017 (127.0.0.1)
2015-04-21T16:31:11.963-0400 connected connection!
connected to: 127.0.0.1:27017
2015-04-21T16:31:11.966-0400 /home/amurty/vespa-db/vespa-db-backup_testing01/vespa/vespastats.bson
2015-04-21T16:31:11.966-0400    going into namespace [vespa.vespastats]
2015-04-21T16:31:11.966-0400     dropping
         file size: 88808161
59724 objects found
2015-04-21T16:31:13.730-0400    Creating index: { key: { _id: 1 }, name: "_id_", ns: "vespa.vespastats" }
2015-04-21T16:31:13.848-0400    Creating index: { key: { url: 1 }, name: "url_1", ns: "vespa.vespastats", background: true }
2015-04-21T16:31:13.858-0400    Creating index: { key: { r_tstpm: 1 }, name: "r_tstpm_1", ns: "vespa.vespastats", background: true }
2015-04-21T16:31:13.859-0400    Creating index: { key: { url: 1, r_tstpm: 1 }, name: "url_1_r_tstpm_1", ns: "vespa.vespastats", background: true }

from /var/log/mongodb/mongod.log - 

2015-04-21T16:31:11.963-0400 [initandlisten] connection accepted from 127.0.0.1:58444 #23 (1 connection now open)
2015-04-21T16:31:11.964-0400 [conn23]  authenticate db: admin { authenticate: 1, nonce: "xxx", user: "admin", key: "xxx" }
2015-04-21T16:31:11.968-0400 [conn23] CMD: drop vespa.vespastats
2015-04-21T16:31:13.757-0400 [conn23] allocating new ns file /var/lib/mongo/vespa.ns, filling with zeroes...
2015-04-21T16:31:13.838-0400 [FileAllocator] allocating new datafile /var/lib/mongo/vespa.0, filling with zeroes...
2015-04-21T16:31:13.846-0400 [FileAllocator] done allocating datafile /var/lib/mongo/vespa.0, size: 64MB,  took 0.007 secs
2015-04-21T16:31:13.847-0400 [conn23] build index on: vespa.vespastats properties: { v: 1, key: { _id: 1 }, name: "_id_", ns: "vespa.vespastats" }
2015-04-21T16:31:13.848-0400 [conn23]    added index to empty collection
2015-04-21T16:31:13.857-0400 [conn23] build index on: vespa.vespastats properties: { v: 1, key: { url: 1 }, name: "url_1", ns: "vespa.vespastats", background: true }
2015-04-21T16:31:13.857-0400 [conn23]    added index to empty collection
2015-04-21T16:31:13.858-0400 [conn23] build index on: vespa.vespastats properties: { v: 1, key: { r_tstpm: 1 }, name: "r_tstpm_1", ns: "vespa.vespastats", background: true }
2015-04-21T16:31:13.859-0400 [conn23]    added index to empty collection
2015-04-21T16:31:13.860-0400 [conn23] build index on: vespa.vespastats properties: { v: 1, key: { url: 1, r_tstpm: 1 }, name: "url_1_r_tstpm_1", ns: "vespa.vespastats", background: true }
2015-04-21T16:31:13.860-0400 [conn23]    added index to empty collection
2015-04-21T16:31:13.862-0400 [conn23] end connection 127.0.0.1:58444 (0 connections now open)

now when i login to my new mongodb instance and check collection size, i get a big 0 - 

# mongo
MongoDB shell version: 2.6.9
connecting to: test
> use vespa
switched to db vespa
> db.auth('vespauser', '<paswd>')
1
> db.vespastats.find()
> db.vespastats.count()
0
>
Quest Monger
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  • Everything looks fine except the lack of docs...what's the count in the original collection (not gotten through the logs)? – wdberkeley Apr 29 '15 at 14:55
  • more data was added to the original DB since i ran that, so the count now stands at - 60841. i obtained that count using db.collectionname.count() – Quest Monger Apr 29 '15 at 19:43

1 Answers1

0

Collection may or may not exist in the used database but the query is not returning an error, just 0.

db.vespastats.find().count()

The issue should be because it is added to database test. (doc mentions it should be automatic but I was able to reproduce this behaviour).

Therefore

use test
db.vespastats.find().count()

would have returned the actual documents in the collection vespastats. The issue is caused by not specifying db name when using mongo binary command mongorestore. doc for mongorestore mongorestore --nsInclude=vesta.vestastats should be the updated version (even if -d still works).

To know where the collection would land, I would run 2 times the restore dump and check show dbs in mongo shell 3 times (before and after) > the db size is changing (not immediately though as it may show 8kb right after the restoration).

Alsushi
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