Database over 2GB in MongoDB

Question

We've got a file-based program we want to convert to use a document database, specifically MongoDB. Problem is, MongoDB is limited to 2GB on 32-bit machines (according to http://www.mongodb.org/display/DOCS/FAQ#FAQ-Whatarethe32bitlimitations%3F), and a lot of our users will have over 2GB of data. Is there a way to have MongoDB use more than one file somehow?

I thought perhaps I could implement sharding on a single machine, meaning I'd run more than one mongod on the same machine and they'd somehow communicate. Could that work?

Answer 1

The best way is managing the virtual storage of MongoDB documents.

The MongoDB's storage limit on different operating systems are tabulated below as per the MongoDB 3.0 MMAPv1 storage engine limits.

The MMAPv1 storage engine limits each database to no more than 16000 data files. This means that a single MMAPv1 database has a maximum size of 32TB. Setting the storage.mmapv1.smallFiles option reduces this limit to 8TB.

Using the MMAPv1 storage engine, a single mongod instance cannot manage a data set that exceeds maximum virtual memory address space provided by the underlying operating system.

                            Virtual Memory Limitations

Operating System           Journaled                Not Journaled

   Linux                 64 terabytes               128 terabytes

Windows Server 2012 R2
and Windows 8.1          64 terabytes               128 terabytes

Windows (otherwise)       4 terabytes                8 terabytes

Reference: MongoDB Database Limit.

Note:The WiredTiger storage engine is not subject to this limitation.

Hope This helps.

Answer 2

The only way to have more than 2GB on a single node is to run multiple mongod processes. So sharding is one option (like you said) or doing some manual partitioning across processes.

Answer 3

You could configure sharding because 2Gb limit only applies to individual mongodb processes. Pls refer the documentation sharded-clusters,and I also found Python Script to set-up sharded environment on a single machine.

#!/usr/bin/python2

import os
import sys
import shutil
import pymongo
import atexit

from socket import error, socket, AF_INET, SOCK_STREAM
from select import select
from subprocess import Popen, PIPE, STDOUT
from threading import Thread
from time import sleep

try:
    # new pymongo
    from bson.son import SON
except ImportError:
    # old pymongo
    from pymongo.son import SON

# BEGIN CONFIGURATION

# some settings can also be set on command line. start with --help to see options

BASE_DATA_PATH='/data/db/sharding/' #warning: gets wiped every time you run this
MONGO_PATH=os.getenv( "MONGO_HOME" , os.path.expanduser('~/10gen/mongo/') )
N_SHARDS=3
N_CONFIG=1 # must be either 1 or 3
N_MONGOS=1
CHUNK_SIZE=64 # in MB (make small to test splitting)
MONGOS_PORT=27017 if N_MONGOS == 1 else 10000 # start at 10001 when multi
USE_SSL=False # set to True if running with SSL enabled

CONFIG_ARGS=[]
MONGOS_ARGS=[]
MONGOD_ARGS=[]

# Note this reports a lot of false positives.
USE_VALGRIND=False
VALGRIND_ARGS=["valgrind", "--log-file=/tmp/mongos-%p.valgrind", "--leak-check=yes", 
               ("--suppressions="+MONGO_PATH+"valgrind.suppressions"), "--"]

# see http://pueblo.sourceforge.net/doc/manual/ansi_color_codes.html
CONFIG_COLOR=31 #red
MONGOS_COLOR=32 #green
MONGOD_COLOR=36 #cyan
BOLD=True

# defaults -- can change on command line
COLLECTION_KEYS = {'foo' : '_id', 'bar': 'key', 'foo2' : 'a,b' }

def AFTER_SETUP():
    # feel free to change any of this
    # admin and conn are both defined globaly
    admin.command('enablesharding', 'test')

    for (collection, keystr) in COLLECTION_KEYS.iteritems():
        key=SON((k,1) for k in keystr.split(','))
        admin.command('shardcollection', 'test.'+collection, key=key)

    admin.command('shardcollection', 'test.fs.files', key={'_id':1})
    admin.command('shardcollection', 'test.fs.chunks', key={'files_id':1})


# END CONFIGURATION

for x in sys.argv[1:]:
    opt = x.split("=", 1)
    if opt[0] != '--help' and len(opt) != 2:
        raise Exception("bad arg: " + x )

    if opt[0].startswith('--'):
        opt[0] = opt[0][2:].lower()
        if opt[0] == 'help':
            print sys.argv[0], '[--help] [--chunksize=200] [--port=27017] [--path=/where/is/mongod] [collection=key]'
            sys.exit()
        elif opt[0] == 'chunksize':
            CHUNK_SIZE = int(opt[1])
        elif opt[0] == 'port':
            MONGOS_PORT = int(opt[1])
        elif opt[0] == 'path':
            MONGO_PATH = opt[1]
        elif opt[0] == 'usevalgrind': #intentionally not in --help
            USE_VALGRIND = int(opt[1])
        else:
            raise( Exception("unknown option: " + opt[0] ) )
    else:
        COLLECTION_KEYS[opt[0]] = opt[1]

if MONGO_PATH[-1] != '/':
    MONGO_PATH = MONGO_PATH+'/'

print( "MONGO_PATH: " + MONGO_PATH )

if not USE_VALGRIND:
    VALGRIND_ARGS = []

# fixed "colors"
RESET = 0
INVERSE = 7

if os.path.exists(BASE_DATA_PATH):
    print( "removing tree: %s" % BASE_DATA_PATH )
    shutil.rmtree(BASE_DATA_PATH)

mongod = MONGO_PATH + 'mongod'
mongos = MONGO_PATH + 'mongos'

devnull = open('/dev/null', 'w+')

fds = {}
procs = []

def killAllSubs():
    for proc in procs:
        try:
            proc.terminate()
        except OSError:
            pass #already dead
atexit.register(killAllSubs)

def mkcolor(colorcode): 
    base = '\x1b[%sm'
    if BOLD:
        return (base*2) % (1, colorcode)
    else:
        return base % colorcode

def ascolor(color, text):
    return mkcolor(color) + text + mkcolor(RESET)

def waitfor(proc, port):
    trys = 0
    while proc.poll() is None and trys < 40: # ~10 seconds
        trys += 1
        s = socket(AF_INET, SOCK_STREAM)
        try:
            try:
                s.connect(('localhost', port))
                return
            except (IOError, error):
                sleep(0.25)
        finally:
            s.close()

    #extra prints to make line stand out
    print
    print proc.prefix, ascolor(INVERSE, 'failed to start')
    print

    sleep(1)
    killAllSubs()
    sys.exit(1)


def printer():
    while not fds: sleep(0.01) # wait until there is at least one fd to watch

    while fds:
        (files, _ , errors) = select(fds.keys(), [], fds.keys(), 1)
        for file in set(files + errors):
            # try to print related lines together
            while select([file], [], [], 0)[0]:
                line = file.readline().rstrip()
                if line:
                    print fds[file].prefix, line
                else:
                    if fds[file].poll() is not None:
                        print fds[file].prefix, ascolor(INVERSE, 'EXITED'), fds[file].returncode
                        del fds[file]
                        break
                break

printer_thread = Thread(target=printer)
printer_thread.start()


configs = []
for i in range(1, N_CONFIG+1):
    path = BASE_DATA_PATH +'config_' + str(i)
    os.makedirs(path)
    config = Popen([mongod, '--port', str(20000 + i), '--configsvr', '--dbpath', path] + CONFIG_ARGS, 
                   stdin=devnull, stdout=PIPE, stderr=STDOUT)
    config.prefix = ascolor(CONFIG_COLOR, 'C' + str(i)) + ':'
    fds[config.stdout] = config
    procs.append(config)
    waitfor(config, 20000 + i)
    configs.append('localhost:' + str(20000 + i))


for i in range(1, N_SHARDS+1):
    path = BASE_DATA_PATH +'shard_' + str(i)
    os.makedirs(path)
    shard = Popen([mongod, '--port', str(30000 + i), '--shardsvr', '--dbpath', path] + MONGOD_ARGS,
                  stdin=devnull, stdout=PIPE, stderr=STDOUT)
    shard.prefix = ascolor(MONGOD_COLOR, 'M' + str(i)) + ':'
    fds[shard.stdout] = shard
    procs.append(shard)
    waitfor(shard, 30000 + i)


#this must be done before starting mongos
for config_str in configs:
    host, port = config_str.split(':')
    config = pymongo.Connection(host, int(port), ssl=USE_SSL).config
    config.settings.save({'_id':'chunksize', 'value':CHUNK_SIZE}, safe=True)
del config #don't leave around connection directly to config server

if N_MONGOS == 1:
    MONGOS_PORT -= 1 # added back in loop

for i in range(1, N_MONGOS+1):
    router = Popen(VALGRIND_ARGS + [mongos, '--port', str(MONGOS_PORT+i), '--configdb' , ','.join(configs)] + MONGOS_ARGS,
                   stdin=devnull, stdout=PIPE, stderr=STDOUT)
    router.prefix = ascolor(MONGOS_COLOR, 'S' + str(i)) + ':'
    fds[router.stdout] = router
    procs.append(router)

    waitfor(router, MONGOS_PORT + i)

conn = pymongo.Connection('localhost', MONGOS_PORT + 1, ssl=USE_SSL)
admin = conn.admin

for i in range(1, N_SHARDS+1):
    admin.command('addshard', 'localhost:3000'+str(i), allowLocal=True)

AFTER_SETUP()

# just to be safe
sleep(2)

print '*** READY ***'
print 
print 

try:
    printer_thread.join()
except KeyboardInterrupt:
    pass