Mongorestore hangs restoring a MongoDB 2.6 dump to a PS for MongoDB 3.0.8 wiredTiger

Hi all,

We are trying to migrate our MongoDB databases but we’re stuck with this issue that seems to occur randomly; some times it hits in an early stage of the restore process, some other times it hits well beyond half of the restore process.

I found someone else posting a similar issue on stackoverflow:…orestore-hangs

OS: CentOS 7 KVM-guest
My mongod.conf file is as follows:
# cat /etc/mongod.conf

# mongod.conf, Percona Server for MongoDB
# for documentation of all options, see:

# Where and how to store data.
dbPath: /var/lib/mongo
enabled: true
# engine: mmapv1
# engine: PerconaFT
# engine: rocksdb
engine: wiredTiger

# Storage engine various options
# mmapv1:
cacheSizeGB: 1

# where to write logging data.
destination: file
logAppend: true
path: /var/log/mongo/mongod.log

fork: true
pidFilePath: /var/run/

# network interfaces
port: 27017





## Enterprise-Only Options:



As you see the cache is reduced to 1Gb as previously Mongo was crashing back to OS, presumably after getting out of memory.

Finally: they say that sometimes a picture is worth a thousand words so

Hi all,

I finally could get along with the restore by enlarging the wiredTiger cacheSizeGB to 2gb.
I’m not sure though that it was strictly an out-of-memory issue because I had a tail -f on the Mongo log file and there was nothing there that could lead me think the cache was getting out of space, so I will keep a close eye on this issue and see how it behaves.

In any case I hope this post can help all of those that may happen to stumble with the same issue.