By default the mongod process sends all output to stdout. You can also specify the daemon to log to file which is necessary for any production implementation. For example:

$ mongod --logpath=`pwd`/mongo.log  &
all output going to: /home/rbradfor/projects/mongo/mongo.log
^C

As you can see there is still a message to stdout, that should be cleaned up for a GA release. The output you will see for a clean startup/shutdown is:

Fri Jun 11 14:05:29 Mongo DB : starting : pid = 7990 port = 27017 dbpath = /home/rbradfor/projects/mongo/data/cu
rrent master = 0 slave = 0  64-bit
Fri Jun 11 14:05:29 db version v1.4.3, pdfile version 4.5
Fri Jun 11 14:05:29 git version: 47ffbdfd53f46edeb6ff54bbb734783db7abc8ca
Fri Jun 11 14:05:29 sys info: Linux domU-12-31-39-06-79-A1 2.6.21.7-2.ec2.v1.2.fc8xen #1 SMP Fri Nov 20 17:48:28
 EST 2009 x86_64 BOOST_LIB_VERSION=1_41
Fri Jun 11 14:05:29 waiting for connections on port 27017
Fri Jun 11 14:05:29 web admin interface listening on port 28017
Fri Jun 11 14:05:31 got kill or ctrl c signal 2 (Interrupt), will terminate after current cmd ends
Fri Jun 11 14:05:31 now exiting
Fri Jun 11 14:05:31  dbexit:
Fri Jun 11 14:05:31 	 shutdown: going to close listening sockets...
Fri Jun 11 14:05:31 	 going to close listening socket: 5
Fri Jun 11 14:05:31 	 going to close listening socket: 6
Fri Jun 11 14:05:31 	 shutdown: going to flush oplog...
Fri Jun 11 14:05:31 	 shutdown: going to close sockets...
Fri Jun 11 14:05:31 	 shutdown: waiting for fs preallocator...
Fri Jun 11 14:05:31 	 shutdown: closing all files...
Fri Jun 11 14:05:31      closeAllFiles() finished
Fri Jun 11 14:05:31 	 shutdown: removing fs lock...
Fri Jun 11 14:05:31  dbexit: really exiting now

MongoDB logging does not give an option to format the date/time appropriately. The format does not match the syslog of Ubuntu/CentOS

Jun  9 10:05:46 barney kernel: [1025968.983209] SGI XFS with ACLs, security attributes, realtime, large block/in
ode numbers, no debug enabled
Jun  9 10:05:46 barney kernel: [1025968.984518] SGI XFS Quota Management subsystem
Jun  9 10:05:46 barney kernel: [1025968.990183] JFS: nTxBlock = 8192, nTxLock = 65536
Jun  9 10:05:46 barney kernel: [1025969.007624] NTFS driver 2.1.29 [Flags: R/O MODULE].
Jun  9 10:05:46 barney kernel: [1025969.020995] QNX4 filesystem 0.2.3 registered.
Jun  9 10:05:46 barney kernel: [1025969.039264] Btrfs loaded

Jun  8 00:00:00 dc1 nagios: CURRENT HOST STATE: localhost;UP;HARD;1;PING OK - Packet loss = 0%, RTA = 0.01 ms
Jun  8 00:00:00 dc1 nagios: CURRENT SERVICE STATE: localhost;Current Load;OK;HARD;1;OK - load average: 0.00, 0.00, 0.00
Jun  8 00:00:00 dc1 nagios: CURRENT SERVICE STATE: localhost;Current Users;OK;HARD;1;USERS OK - 2 users currently logged in
Jun  8 00:00:00 dc1 nagios: CURRENT SERVICE STATE: localhost;HTTP;CRITICAL;HARD;4;Connection refused
Jun  8 00:00:00 dc1 nagios: CURRENT SERVICE STATE: localhost;PING;OK;HARD;1;PING OK - Packet loss = 0%, RTA = 0.01 ms
Jun  8 00:00:00 dc1 nagios: CURRENT SERVICE STATE: localhost;Root Partition;OK;HARD;1;DISK OK - free space: / 107259 MB (49% inode=98%):
Jun  8 00:00:00 dc1 nagios: CURRENT SERVICE STATE: localhost;SSH;OK;HARD;1;SSH OK - OpenSSH_4.3 (protocol 2.0)

And for reference here is the mysql format, which is also not configurable.

100605 16:43:38 mysqld_safe Starting mysqld daemon with databases from /opt/mysql51/data
100605 16:43:38 [Warning] '--log_slow_queries' is deprecated and will be removed in a future release. Please use ''--slow_query_log'/'--slow_query_log_fi
le'' instead.
100605 16:43:38 [Warning] '--log' is deprecated and will be removed in a future release. Please use ''--general_log'/'--general_log_file'' instead.
100605 16:43:38 [Warning] No argument was provided to --log-bin, and --log-bin-index was not used; so replication may break when this MySQL server acts a
s a master and has his hostname changed!! Please use '--log-bin=dc1-bin' to avoid this problem.
/opt/mysql51/bin/mysqld: File './dc1-bin.index' not found (Errcode: 13)
100605 16:43:38 [ERROR] Aborting

However unlike other products including MySQL the next execution of the mongod process overwrites the log file. This will catch some administrators out. You need to remember to also add –logappend. Personally I’d prefer to see this is the default

$ mongod --logpath=`pwd`/mongo.log --logappend

I did observe some confusion on messaging. Using the mongo shell you get a jumble of logging messages during a shutdown.

$ mongo
MongoDB shell version: 1.4.3
url: test
connecting to: test
type "help" for help
> use admin
switched to db admin
> db.shutdownServer();
Fri Jun 11 13:54:08 query failed : admin.$cmd { shutdown: 1.0 } to: 127.0.0.1
server should be down...
Fri Jun 11 13:54:08 trying reconnect to 127.0.0.1
Fri Jun 11 13:54:08 reconnect 127.0.0.1 ok
Fri Jun 11 13:54:08 query failed : admin.$cmd { getlasterror: 1.0 } to: 127.0.0.1
Fri Jun 11 13:54:08 JS Error: Error: error doing query: failed (anon):1284
> exit
bye

This also results in an unformatted message in the log file for some reason.

$ tail mongo.log
Fri Jun 11 13:54:08 	 shutdown: removing fs lock...
Fri Jun 11 13:54:08  dbexit: really exiting now
Fri Jun 11 13:54:08 got request after shutdown()
ERROR: Client::~Client _context should be NULL: conn

Nothing of any critical nature however all important for system administrators that have monitoring scripts or using monitoring products.

MongoDB is categorized as a schema-less, schema-free or a document orientated data store. Another category of NoSQL product is the key/value store. It had not dawned on me until a discussion with some of the 10gen employees that MongoDB is also a key/value store, this is just a subset of features.

How would you consider the design of a key/value store? Using the memached model, there are 4 primary attributes to consider:

• The Key to store/retrieve
• The Value for the given key
• An auto expiry of the cached data
• A key scope enabling multiple namespaces

There are three primary functions:

• Put a given Key/Value pair
• Get a given Key
• Delete a given Key

Let’s explore the options. The first is to create a new collection for each key. That way there is only one row per key,

> use keystore
> var d = new Date();
> var id = "key1";
> var kv = { key: id,val: "Hello World",expires: d}
> db.key1.save(kv);
> db.key1.find();
{ "_id" : ObjectId("4c126095c68fcaf3b0e07a2b"), "key" : "key1", "val" : "Hello World", "expires" : "Fri Jun 11 2010 12:09:51 GMT-0400 (EDT)" }

However when we start loading we run into a problem.

> db.key99999.save({key: "key99999", val: "Hello World", expires: new Date()})
too many namespaces/collections
> show collections;
Fri Jun 11 12:49:02 JS Error: uncaught exception: error: {
	"$err" : "too much key data for sort() with no index.  add an index or specify a smaller limit"
}
> db.stats()
{
	"collections" : 13661,
	"objects" : 26118,
	"dataSize" : 2479352,
	"storageSize" : 93138688,
	"numExtents" : 13665,
	"indexes" : 13053,
	"indexSize" : 106930176,
	"ok" : 1
}

I did read there was a limit on the number of collections at Using a Large Number of Collections.
Also for reference, I look at the underlying data files shows the ^2 increment of data files.

$ ls -lh data/current
total 2.2G
-rw------- 1 rbradfor rbradfor  64M 2010-06-11 12:45 keystore.0
-rw------- 1 rbradfor rbradfor 128M 2010-06-11 12:45 keystore.1
-rw------- 1 rbradfor rbradfor 256M 2010-06-11 12:46 keystore.2
-rw------- 1 rbradfor rbradfor 512M 2010-06-11 12:48 keystore.3
-rw------- 1 rbradfor rbradfor 1.0G 2010-06-11 12:48 keystore.4
-rw------- 1 rbradfor rbradfor  16M 2010-06-11 12:48 keystore.ns

> db.dropDatabase();
{ "dropped" : "keystore.$cmd", "ok" : 1 }

In my next test I’ll repeat by adding the key as a row or document for just one collection.

The best way to learn any new product is to a) read the manual, and b) start using the product.

I created a simple sample application so I could understand the various functions including adding data, searching as well as management functions etc. As with any good sample application using a source of data that already exists always makes life easier. For this example I’m going to use the Operating System output so I will have an ever increasing amount of output for no additional work.

I will be starting with a database called ‘stats’. For this database my first collection is going to be called ‘system’ and this is going to record the most basic of information including date/time, host and cpu (user,sys,idle) stats. I have a simple shell script that creates an appropriate JSON string and I use mongoimport to load the data. Here is my Version 0.1 architectural structure.

mongo> use stats;
mongo> db.system.findOne();
{
	"_id" : ObjectId("4c11183580399ad2db4f503b"),
	"host" : "barney",
	"epoch" : 1276188725,
	"date" : "Thu Jun 10 12:52:05 EDT 2010",
	"cpu" : {
		"user" : 2,
		"sys" : 2,
		"idle" : 95
	},
	"raw" : " 11435699 1379565 9072198 423130352 2024835 238766 2938641 0 0"
}

I made some initial design decisions before I understand the full strengths/limitation of MongoDB as well as what my actual access paths to data will be.
While I’m using a seconds since epoch for simple range searching, I’m adding a presentation date for user readability. I’ve created a different sub element for cpu, because it a) this element has a number of individual attributes I will want to report and search on, and b) this collection should be extended to include other information like load average, running processes, memory etc.

If my shell script runs in debug mode, I also record the raw data used to determine the end result. This makes debugging easier.

Here is my first query.

Find all statistics between two dates. It took a bit of getting the correct construct syntax correct, $le and $ge didn’t work so RTFM highlighted the correct syntax. I also first included elements for epoch, which resulted in a OR condition, I see you can add multiple comparison operators to a single element to get an AND operation.

mongo> db.system.find({epoch: { $gte: 1276188725, $lte: 1276188754}});
{ "_id" : ObjectId("4c11183580399ad2db4f503b"), "host" : "barney", "epoch" : 1276188725, "date" : "Thu Jun 10 12:52:05 EDT 2010", "cpu" : { "user" : 2, "sys" : 2, "idle" : 95 }, "raw" : " 11435699 1379565 9072198 423130352 2024835 238766 2938641 0 0" }
{ "_id" : ObjectId("4c11184c80399ad2db4f503c"), "host" : "barney", "epoch" : 1276188748, "date" : "Thu Jun 10 12:52:28 EDT 2010", "cpu" : { "user" : 2, "sys" : 2, "idle" : 95 }, "raw" : " 11436605 1379565 9072320 423138450 2024862 238770 2938641 0 0" }
{ "_id" : ObjectId("4c11185080399ad2db4f503d"), "host" : "barney", "epoch" : 1276188752, "date" : "Thu Jun 10 12:52:32 EDT 2010", "cpu" : { "user" : 2, "sys" : 2, "idle" : 95 }, "raw" : " 11437005 1379565 9072330 423139527 2024862 238770 2938641 0 0" }
{ "_id" : ObjectId("4c11185180399ad2db4f503e"), "host" : "barney", "epoch" : 1276188753, "date" : "Thu Jun 10 12:52:33 EDT 2010", "cpu" : { "user" : 2, "sys" : 2, "idle" : 95 }, "raw" : " 11437130 1379565 9072334 423139862 2024862 238770 2938641 0 0" }
{ "_id" : ObjectId("4c11185280399ad2db4f503f"), "host" : "barney", "epoch" : 1276188754, "date" : "Thu Jun 10 12:52:34 EDT 2010", "cpu" : { "user" : 2, "sys" : 2, "idle" : 95 }, "raw" : " 11437316 1379565 9072338 423140325 2024910 238770 2938641 0 0" }

Assuming I’m going to have stats from more then one server in my data, we should always filter by hostname, and then for given period.

mongo> db.system.find({host: "barney", epoch: { $gte: 1276188725, $lte: 1276188754}});

If I only want to see the Date/Time and CPU stats, I can show a subset of the elements found.

mongo> db.system.find({epoch: { $gte: 1276188725, $lte: 1276188754}}, {date:1,cpu:1});
{ "_id" : ObjectId("4c11183580399ad2db4f503b"), "date" : "Thu Jun 10 12:52:05 EDT 2010", "cpu" : { "user" : 2, "sys" : 2, "idle" : 95 } }
{ "_id" : ObjectId("4c11184c80399ad2db4f503c"), "date" : "Thu Jun 10 12:52:28 EDT 2010", "cpu" : { "user" : 2, "sys" : 2, "idle" : 95 } }
...

Filtering on a sub-element is also possible however I found that the representation of strings and numbers does not do an implied conversion. In the following example “2” does not match any results, while 2 does.

mongo> db.system.findOne({host: "barney", "cpu.user": "2"})
null


mongo> db.system.findOne({host: "barney", "cpu.user": 2})
{
	"_id" : ObjectId("4c11161680399ad2db4f5033"),
	"host" : "barney",
	"epoch" : 1276188182,
	"date" : "Thu Jun 10 12:43:02 EDT 2010",
	"cpu" : {
		"user" : 2,
		"sys" : 2,
		"idle" : 95
	}
}

Given the collection and load process works, data is being recorded and I can perform some searching I now have the basis for adding additional rich data elements, learning about the internal DBA operations possible after I fix the bug with all my values being 2/2/95.

In my earlier tests I bulk loaded data with the following command.

mongoimport -d olympics -c olympic_event -type tsv --headerline -f name,id,sport,demonstration_competitions,olympic_games_contested,competitions,contested_as_demonstration_event --drop olympic_event.tsv
connected to: 127.0.0.1
dropping: olympics.olympic_event
imported 775 objects

As you can see I imported 775 objects, however when I went to review them via the mongo interactive shell I found no data.

> use olympics;
switched to db olympics
> db.olypics.olympic_event.find();
# No results?

I was able to confirm these objects were in the namespace.

> db.system.namespaces.find();
{ "name" : "olympics.system.indexes" }
{ "name" : "olympics.demonstration_event_athlete_relationship" }
{ "name" : "olympics.demonstration_event_athlete_relationship.$_id_" }
{ "name" : "olympics.olympic_athlete" }
{ "name" : "olympics.olympic_athlete.$_id_" }
{ "name" : "olympics.olympic_athlete_affiliation" }
{ "name" : "olympics.olympic_athlete_affiliation.$_id_" }
{ "name" : "olympics.olympic_bidding_city" }
{ "name" : "olympics.olympic_bidding_city.$_id_" }
{ "name" : "olympics.olympic_city_bid" }
{ "name" : "olympics.olympic_city_bid.$_id_" }
{ "name" : "olympics.olympic_demonstration_competition" }
{ "name" : "olympics.olympic_demonstration_competition.$_id_" }
{ "name" : "olympics.olympic_demonstration_medal_honor" }
{ "name" : "olympics.olympic_demonstration_medal_honor.$_id_" }
{ "name" : "olympics.olympic_event" }
{ "name" : "olympics.olympic_event.$_id_" }
{ "name" : "olympics.olympic_event_competition" }
{ "name" : "olympics.olympic_event_competition.$_id_" }
{ "name" : "olympics.olympic_games" }
has more
> it
{ "name" : "olympics.olympic_games.$_id_" }
{ "name" : "olympics.olympic_host_city" }
{ "name" : "olympics.olympic_host_city.$_id_" }
{ "name" : "olympics.olympic_mascot" }
{ "name" : "olympics.olympic_mascot.$_id_" }
{ "name" : "olympics.olympic_medal" }
{ "name" : "olympics.olympic_medal.$_id_" }
{ "name" : "olympics.olympic_medal_demonstration" }
{ "name" : "olympics.olympic_medal_demonstration.$_id_" }
{ "name" : "olympics.olympic_medal_honor" }
{ "name" : "olympics.olympic_medal_honor.$_id_" }
{ "name" : "olympics.olympic_participating_country" }
{ "name" : "olympics.olympic_participating_country.$_id_" }
{ "name" : "olympics.olympic_sport" }
{ "name" : "olympics.olympic_sport.$_id_" }
{ "name" : "olympics.olympic_venue" }
{ "name" : "olympics.olympic_venue.$_id_" }

The problem is I was using the namespace object with db.find(), not the collection object. I am already in the database scope with the use command.

Knowing this I get what I expected with the correct collection name.

> db.olympic_event.find();
{ "_id" : ObjectId("4c0fb666a5cd86585be7c0fd"), "name" : "Men's Boxing, Super Heavyweight +91kg", "id" : "/guid/9202a8c04000641f8000000008d88df9", "sport" : "Boxing", "demonstration_competitions" : "", "olympic_games_contested" : "2008 Summer Olympics,1984 Summer Olympics,2000 Summer Olympics,2004 Summer Olympics,1988 Summer Olympics,1996 Summer Olympics,1992 Summer Olympics", "competitions" : "Boxing at the 1984 Summer Olympics - Super Heavyweight ,Boxing at the 2000 Summer Olympics - Super Heavyweight,Boxing at the 1988 Summer Olympics - Super Heavyweight ,Boxing at the 2004 Summer Olympics - Super Heavyweight,Boxing at the 1992 Summer Olympics - Super Heavyweight ,Boxing at the 2008 Summer Olympics - Super heavyweight,Boxing at the 1996 Summer Olympics - Super Heavyweight" }
{ "_id" : ObjectId("4c0fb666a5cd86585be7c0fe"), "name" : "Men's Judo, 60 - 66kg (half-lightweight)", "id" : "/guid/9202a8c04000641f8000000008d88d0e", "sport" : "Judo", "demonstration_competitions" : "", "olympic_games_contested" : "2004 Summer Olympics,2000 Summer Olympics,2008 Summer Olympics", "competitions" : "Judo at the 2008 Summer Olympics – Men's Half Lightweight (66 kg),Judo at the 2000 Summer Olympics - Men's Half Lightweight (66 kg),Judo at the 2004 Summer Olympics - Men's Half Lightweight (66 kg)" }
{ "_id" : ObjectId("4c0fb666a5cd86585be7c0ff"), "name" : "Men's Tennis, Indoor Singles", "id" : "/guid/9202a8c04000641f8000000010be70e8", "sport" : "Tennis", "demonstration_competitions" : "", "olympic_games_contested" : "1912 Summer Olympics,1908 Summer Olympics", "competitions" : "Tennis at the 1908 Summer Olympics - Men's Indoor Singles,Tennis at the 1912 Summer Olympics - Men's Indoor Singles" }
...

It’s interesting that a collection name can contain a fullstop ‘.’ which is the delimiter in the command syntax. In my earlier observation I was not getting an error, only an empty response. For example you can do this.

> use test;
switched to db test
> db.foo.x.save({a: 1});
> db.foo.x.find();
{ "_id" : ObjectId("4c0fc1784ff83a6831364d57"), "a" : 1 }

You can very easily find out the running threads in the database (e.g. like a MySQL SHOW PROCESSLIST) with db.currentOp.

> db.currentOp();
{ "inprog" : [ ] }

No much happening, however under some load you can see

> db.currentOp();
{
	"inprog" : [
		{
			"opid" : 27980,
			"active" : true,
			"lockType" : "write",
			"waitingForLock" : false,
			"secs_running" : 0,
			"op" : "insert",
			"ns" : "olympics.olympic_athlete",
			"client" : "127.0.0.1:63652",
			"desc" : "conn"
		}
	]
}
> db.currentOp();
{
	"inprog" : [
		{
			"opid" : 57465,
			"active" : true,
			"lockType" : "write",
			"waitingForLock" : false,
			"secs_running" : 0,
			"op" : "insert",
			"ns" : "olympics.olympic_athlete_affiliation",
			"client" : "127.0.0.1:63653",
			"desc" : "conn"
		}
	]
}

I was able to see these when I was Bulk Loading Data

The HTTPConsole at http://localhost:28017/ (for default installation) also shows you all client connections as well as more information per thread, database uptime, replication status and a DBTOP for recent namespaces. For example:

mongodb mactazosx.local:27017

db version v1.4.3, pdfile version 4.5
git hash: 47ffbdfd53f46edeb6ff54bbb734783db7abc8ca
sys info: Darwin broadway.local 9.8.0 Darwin Kernel Version 9.8.0: Wed Jul 15 16:55:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_I386 i386 BOOST_LIB_VERSION=1_40

dbwritelocked:  0 (initial)
uptime:    2851 seconds

assertions:

replInfo:

Clients:
Thread	OpId	Active	LockType	Waiting	SecsRunning	Op	NameSpace	Query	client	msg	progress
initandlisten	0		1			2004	test	{ name: /^local.temp./ }	0.0.0.0:0
snapshotthread	0		0			0			0.0.0.0:0
websvr	18		-1			2004	test._defaultCollection	{}	0.0.0.0:0
conn	83741		-1			2004	olympics.olympic_host_city	{}	127.0.0.1:63268
conn	83739		0			2004	?	{ getlasterror: 1.0 }	127.0.0.1:63756

time to get dblock: 0ms
# databases: 3
Cursors byLoc.size(): 0

replication
master: 0
slave:  0
initialSyncCompleted: 1

DBTOP  (occurences|percent of elapsed)
NS	total	Reads	Writes	Queries	GetMores	Inserts	Updates	Removes
GLOBAL	1	0.00%	1	0.00%	0	0.00%	1	0.00%	0	0.00%	0	0.00%	0	0.00%	0	0.00%
olympics.olympic_host_city	1	0.00%	1	0.00%	0	0.00%	1	0.00%	0	0.00%	0	0.00%	0	0.00%	0	0.00%

It was interesting to see a whatsmyuri command. Will need to investigate that further.

mongoDB has a mongoimport command. The docs only shows the usage but not any examples. here are my first examples.

data1.csv

1
2
3
4
5
6
7
8
9
0

You need to specify your database (-d) and collection (-c) for importing. In my example, I also specified the collection fields with (-f)

The –file is actually optional, specifying the filename as the large argument also works.

mongoimport -d test -c foo -f a -type csv data
connected to: 127.0.0.1
imported 10 objects

NOTE: The default type is JSON, so you can get some nasty errors if you forget the csv type.

Wed Jun  9 11:18:26 Assertion: 10340:Failure parsing JSON string near: 1
0x68262 0x23968 0x250563 0x251c7b 0x24cb00 0x250280 0x1af6
 0   mongoimport                         0x00068262 _ZN5mongo11msgassertedEiPKc + 514
 1   mongoimport                         0x00023968 _ZN5mongo8fromjsonEPKc + 520
 2   mongoimport                         0x00250563 _ZN6Import9parseLineEPc + 131
 3   mongoimport                         0x00251c7b _ZN6Import3runEv + 2635
 4   mongoimport                         0x0024cb00 _ZN5mongo4Tool4mainEiPPc + 2880
 5   mongoimport                         0x00250280 main + 496
 6   mongoimport                         0x00001af6 start + 54
exception:Failure parsing JSON string near: 1

In my second example I’m adding multiple fields. This time my data file also has a headers which you can ignore with (–headerline)

data2.csv

name, age
Mickey Mouse,65
Minnie Mouse,64
Donald Duck,
Taz Devil,22
Marvin the Martian,45

$ mongoimport -d test -c foo -f name,age -type csv --headerline data2.csv
connected to: 127.0.0.1
imported 6 objects

> db.foo.find();
...
{ "_id" : ObjectId("4c0fb0dfa5cd86585be6ca63"), "a" : 0 }
{ "_id" : ObjectId("4c0fb2bea5cd86585be6ca64"), "name" : "Mickey Mouse", "age" : 65 }
{ "_id" : ObjectId("4c0fb2bea5cd86585be6ca65"), "name" : "Minnie Mouse", "age" : 64 }
{ "_id" : ObjectId("4c0fb2bea5cd86585be6ca66"), "name" : "Donald Duck" }
{ "_id" : ObjectId("4c0fb2bea5cd86585be6ca67"), "name" : "Taz Devil", "age" : 22 }
{ "_id" : ObjectId("4c0fb2bea5cd86585be6ca68"), "name" : "Marvin the Martian", "age" : 45 }

You can also use the –drop argument to truncate your collection before loading.

Real Data

I’m going to use the Freebase Olympics data to perform a more robust test.

wget http://download.freebase.com/datadumps/2010-04-15/browse/olympics.tar.bz2
bunzip2 olympics.tar.bz2
tar xvf olympics.tar
cd olympics

Loading this data via the following convenience script gave me some more meaningful data.

> db.olympic_host_city.find();
{ "_id" : ObjectId("4c0fb666a5cd86585be7d9b6"), "name" : "Vancouver", "id" : "/guid/9202a8c04000641f80000000000401e2", "olympics_hosted" : "2010 Winter Olympics" }
{ "_id" : ObjectId("4c0fb666a5cd86585be7d9b7"), "name" : "Moscow", "id" : "/guid/9202a8c04000641f800000000002636c", "olympics_hosted" : "1980 Summer Olympics" }
{ "_id" : ObjectId("4c0fb666a5cd86585be7d9b8"), "name" : "St. Moritz", "id" : "/guid/9202a8c04000641f80000000001c33e8", "olympics_hosted" : "1948 Winter Olympics,1928 Winter Olympics" }
...

Here is the simple load script I used.

#!/bin/sh

load_file() {
  local INPUT_FILE=$1
  [ -z "${INPUT_FILE}" ] && echo "ERROR: File not specified" && return 1

  echo "Loading file ${INPUT_FILE}"

  COLLECTION=`echo ${INPUT_FILE} | cut -d. -f1`

  FIELDS=`head -1 ${INPUT_FILE} | sed -e "s/	/,/g;s/ /_/g"`
  echo "mongoimport -d olympics -c ${COLLECTION} -type tsv --headerline -f $FIELDS --drop ${INPUT_FILE}"
  time mongoimport -d olympics -c ${COLLECTION} -type tsv --headerline -f $FIELDS --drop ${INPUT_FILE}
  return 0
}

process_dir() {

  echo "Processing" `pwd`
  for FILE in `ls *.tsv`
  do
    load_file ${FILE}
  done

  return 0
}

main() {
  process_dir
}

main $*
exit 0

Following the initial Quickstart docs you will find a lot of online documentation. The following are good places to start.

• Tutorial
• The Interactive Shell
• Manual
• Admin Zone
  • Starting and Stopping
  • Monitoring and Diagnostics
  • Backups

There is also a Getting Started however I found this a duplication of the Quickstart. I have not found an offline version of the manual, or a single HTML page version. This makes it a little difficult for reading without internet connectivity.

You can find information at the Official Blog. While I found no Blog Roll, one developer Kyle Banker has a blog.

There are several Mailing Lists available however It seems your best help may be via IRC at irc://irc.freenode.net/#mongodb I found over 200 members on the channel.

There are currently no books on MongoDB however there seems to be 4 books in the making.

Getting started with MongoDB is relatively straight forward, following the instructions from the Quickstart guide has you operational in a few minutes.

I like projects that provide a latest version link for software. There is no need to update any documentation or blog posts over time. The current instructions require some additional steps when creating the initial data directory, due to normal permissions of the root directory. This is the only pre-requisite to using the software out of the box. There is no additional configuration required for a default installation.

$ sudo mkdir /data/db
$ sudo chown `id -u` /data/db

I ran a few boundary tests to verify the error handling of the initial startup process.

The following occurs when the data directory does not exist.

$ ./mongodb-osx-i386-1.4.3/bin/mongod
./mongodb-osx-i386-1.4.3/bin/mongod --help for help and startup options
Tue Jun  8 15:59:52 Mongo DB : starting : pid = 78161 port = 27017 dbpath = /data/db/ master = 0 slave = 0  32-bit

** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data
**       see http://blog.mongodb.org/post/137788967/32-bit-limitations for more

Tue Jun  8 15:59:52 Assertion: 10296:dbpath (/data/db/) does not exist
0x68572 0x247814 0x24821a 0x24a855 0x1e06
 0   mongod                              0x00068572 _ZN5mongo11msgassertedEiPKc + 514
 1   mongod                              0x00247814 _ZN5mongo14_initAndListenEiPKc + 548
 2   mongod                              0x0024821a _ZN5mongo13initAndListenEiPKc + 42
 3   mongod                              0x0024a855 main + 4917
 4   mongod                              0x00001e06 start + 54
Tue Jun  8 15:59:52   exception in initAndListen std::exception: dbpath (/data/db/) does not exist, terminating
Tue Jun  8 15:59:52  dbexit:
Tue Jun  8 15:59:52 	 shutdown: going to close listening sockets...
Tue Jun  8 15:59:52 	 shutdown: going to flush oplog...
Tue Jun  8 15:59:52 	 shutdown: going to close sockets...
Tue Jun  8 15:59:52 	 shutdown: waiting for fs preallocator...
Tue Jun  8 15:59:52 	 shutdown: closing all files...
Tue Jun  8 15:59:52      closeAllFiles() finished
Tue Jun  8 15:59:52  dbexit: really exiting now

The following error occurs when the user has insufficient permissions for the directory.

$ sudo mkdir /data/db
$ ./mongodb-osx-i386-1.4.3/bin/mongod
./mongodb-osx-i386-1.4.3/bin/mongod --help for help and startup options
Tue Jun  8 16:01:52 Mongo DB : starting : pid = 78178 port = 27017 dbpath = /data/db/ master = 0 slave = 0  32-bit

** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data
**       see http://blog.mongodb.org/post/137788967/32-bit-limitations for more

Tue Jun  8 16:01:52 User Exception 10309:Unable to create / open lock file for dbpath: /data/db/mongod.lock
Tue Jun  8 16:01:52   exception in initAndListen std::exception: Unable to create / open lock file for dbpath: /data/db/mongod.lock, terminating
Tue Jun  8 16:01:52  dbexit:
Tue Jun  8 16:01:52 	 shutdown: going to close listening sockets...
Tue Jun  8 16:01:52 	 shutdown: going to flush oplog...
Tue Jun  8 16:01:52 	 shutdown: going to close sockets...
Tue Jun  8 16:01:52 	 shutdown: waiting for fs preallocator...
Tue Jun  8 16:01:52 	 shutdown: closing all files...
Tue Jun  8 16:01:52      closeAllFiles() finished
Tue Jun  8 16:01:52 	 shutdown: removing fs lock...
Tue Jun  8 16:01:52 	 couldn't remove fs lock errno:9 Bad file descriptor
Tue Jun  8 16:01:52  dbexit: really exiting now

A missing step from the existing documentation is to set appropriate permissions to the data directory so that mongod run as your normal user can write to the directory.

$ sudo chown `id -u` /data/db
$ ./mongodb-osx-i386-1.4.3/bin/mongod

Tue Jun  8 16:06:37 Mongo DB : starting : pid = 78284 port = 27017 dbpath = /data/db/ master = 0 slave = 0  32-bit

** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data
**       see http://blog.mongodb.org/post/137788967/32-bit-limitations for more

Tue Jun  8 16:06:37 db version v1.4.3, pdfile version 4.5
Tue Jun  8 16:06:37 git version: 47ffbdfd53f46edeb6ff54bbb734783db7abc8ca
Tue Jun  8 16:06:37 sys info: Darwin broadway.local 9.8.0 Darwin Kernel Version 9.8.0: Wed Jul 15 16:55:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_I386 i386 BOOST_LIB_VERSION=1_40
Tue Jun  8 16:06:37 waiting for connections on port 27017
Tue Jun  8 16:06:37 web admin interface listening on port 28017

You are then ready to rock and roll. Use the exit command to exit the mongo interactive shell.

$ ./mongodb-osx-i386-1.4.3/bin/mongo
> db.foo.save ({a:2});
> db.foo.find();
{ "_id" : ObjectId("4c0ea308f5ea2f7148a33b9f"), "a" : 2 }
> exit
bye

The mongod output of the first save of data into the “foo” collection shows a little of how mongodb operations. There is a lazy instantiation of “test” database when first required. There is no need to first create this, or use this as with MySQL.

Tue Jun  8 16:07:36 allocating new datafile /data/db/test.ns, filling with zeroes...
Tue Jun  8 16:07:36 done allocating datafile /data/db/test.ns, size: 16MB, took 0.05 secs
Tue Jun  8 16:07:37 allocating new datafile /data/db/test.0, filling with zeroes...
Tue Jun  8 16:07:38 done allocating datafile /data/db/test.0, size: 64MB, took 1.282 secs
Tue Jun  8 16:07:40 building new index on { _id: 1 } for test.foo
Tue Jun  8 16:07:40 Buildindex test.foo idxNo:0 { name: "_id_", ns: "test.foo", key: { _id: 1 } }
Tue Jun  8 16:07:40 done for 0 records 0.018secs
Tue Jun  8 16:07:40 insert test.foo 3181ms

$ ls -l /data/db
total 163848
drwxr-xr-x  2 rbradfor  admin        68 Jun  8 16:07 _tmp
-rwxr-xr-x  1 rbradfor  admin         6 Jun  8 16:06 mongod.lock
-rw-------  1 rbradfor  admin  67108864 Jun  8 16:07 test.0
-rw-------  1 rbradfor  admin  16777216 Jun  8 16:07 test.ns

One observation is the output of the mongod is more a trace output. I have yet to see any information about a more appropriately formatted error log.

My first exposure to MongoDB was in July 2008 when I was a panelist on “A Panel on Cloud Computing” at the Entrepreneurs Round Table in New York. The panel included a representative from 10gen the company behind the open source database product and at the time Mongo was described as a full stack solution with the database being only one future component.

While I mentioned Mongo again in a blog in Nov 2008, it was not until Oct 6 2009 at the NoSQL event in New York where I saw a more stable product and a revised focus of development just on the database component.

As the moderator for the closing keynote “SQL v NOSQL” panel at Open SQL Camp 2009 in Portland, Oregon I had the chance to discuss MongoDB with the other products in the NoSQL space. Watch Video

In just the past few weeks, 3 people independently have mentioned MongoDB and asked for my input. I was disappointed to just miss the MongoNYC 2010 event.

While I have evaluated various new products in the key/value store and the schemaless space, my curiosity has been initially more with Cassandra and CouchDB.

Follow my journey as I explore in more detail the usage of mongoDB {name: “mongo”, type:”db”} via the mongodb tag on my blog.