Importing data into a MongoDB database using Kettle from a csv file

In a previous post we saw how to import data into a MongoDB database from a cvs file using mongoimport. In this post we will import data into the MongoDB database from a cvs file using Kettle.

This youtube video show how to import data from a text file into MongoDB
http://www.youtube.com/watch?v=Tgyrd1UiQhE

The screen below shows the configuration of the CSV input

The screen below show the configuration of the MogoDB output

The below screen shows the transformation between the CVS file input ->  MongoDB output was created, and run.

Next we will connect to MongoDB, to see if the data has been indeed imported. Connect to the mongo shell

> use mydbdemo switched to db mydbdemo > db.projects.find().toArray() [         {                 "_id" : ObjectId("527d4e5e73ca0be1b2bc2504"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "SVC",                 "Project" : "SVC Chubby nodes and Oracle",                 "Owner" : "Mayur"         },         {                 "_id" : ObjectId("527d4e5e73ca0be1b2bc2505"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "IBM Tape",                 "Project" : "Oracle backup",                 "Owner" : "Shashank"         },         {                 "_id" : ObjectId("527d4e5e73ca0be1b2bc2506"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "V7000",                 "Project" : "Oracle 12c on V7000",                 "Owner" : "Mayur"         },         {                 "_id" : ObjectId("527d4e5e73ca0be1b2bc2507"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "DS8870",                 "Project" : "Easy Tier 5 for Oracle",                 "Owner" : "Mayur"         } ]

We can also import data directly from a Microsoft Excel spreadsheet into MongoDB using Kettle.

Importing data into a MongoDB database using mongoimport from a csv file

I want to import some data from a xml spreadsheet, and load it into a MongoDB database. To do that, the first step is to convert the xml data into a csv file, and then load that data into a MongoDB database using mongoimport.

Below I tried to import a simple csv file into a mongodb database using mongoimport.

Here is my sample csv file:

[root@isvx7 mongodb_new]# cat projects.csv ISV Name,Storage Brand,Project,Owner Oracle,SVC,SVC Chubby nodes and Oracle,Mayur Oracle,IBM Tape,Oracle backup,Shashank Oracle,V7000,Oracle 12c on V7000,Mayur Oracle,DS8870,Easy Tier 5 for Oracle,Mayur

The version of MongoDB that I'm currently running

[root@isvx7 mongodb_new]# mongod -version db version v2.4.8 Tue Nov  5 16:30:37.367 git version: a350fc38922fbda2cec8d5dd842237b904eafc14

Executing the mongoimport command on the same host running the mongodb server.

[root@isvx7 mongodb_new]# mongoimport --db mydb --collection projects --type csv --file ./projects.csv --headerline connected to: 127.0.0.1 Tue Nov  5 15:47:08.606 imported 4 objects

As seen on the mongo shell

> show dbs mydb    0.203125GB > use mydb switched to db mydb > db.projects.find().toArray() [         {                 "_id" : ObjectId("5279756a601c0948fdb32f70"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "SVC",                 "Project" : "SVC Chubby nodes and Oracle",                 "Owner" : "Mayur"         },         {                 "_id" : ObjectId("5279756c601c0948fdb32f71"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "IBM Tape",                 "Project" : "Oracle backup",                 "Owner" : "Shashank"         },         {                 "_id" : ObjectId("5279756c601c0948fdb32f72"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "V7000",                 "Project" : "Oracle 12c on V7000",                 "Owner" : "Mayur"         },         {                 "_id" : ObjectId("5279756c601c0948fdb32f73"),                 "ISV Name" : "Oracle",                 "Storage Brand" : "DS8870",                 "Project" : "Easy Tier 5 for Oracle",                 "Owner" : "Mayur"         } ] >

Configuring MongoDB Replication on RedHat Linux nodes

In this post I’ll look at configuring replication in MongoDB. In my setup I have 2 x RedHat Linux nodes that will act as the Primary and Secondary for my MongoDB replication set.

I began by downloading MongoDB on both the nodes of the replication set.

[root@isvx7 ~]# cd mongodb [root@isvx7 ~]# wget ftp://ftp.muug.mb.ca/mirror/fedora/epel/5/x86_64/ganglia-3.0.7-1.el5.x86_64.rpm [root@isvx7 mongodb]# ls mongodb-linux-x86_64-2.2.0      mongodb-linux-x86_64-2.2.0.tar [root@isvx7 mongodb]#

My MongoDB replication set will be called liverpool, and “anfield1” and “anfield2” will be the two dbpaths on each of the nodes respectively.

[root@isvx7 ~]# mkdir anfield1 [root@isvx3 ~]# mkdir anfield2

Next I started the mongod server passing it the replication set name, and the dbpath. I also use port 27001 and limited the oplogSize to 50

[root@isvx7 ~]# mongod --replSet liverpool --dbpath anfield1 --port 27001 --oplogSize 50 <some related configuration messages> Fri Nov 30 16:13:36 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG) Fri Nov 30 16:13:46 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)

Next I went and did the same thing on the other node ie. isvx3

[root@isvx3 ~]# mongod --replSet liverpool --dbpath anfield2 --port 27001 --oplogSize 50 <some related configuration messages> Fri Nov 30 15:17:17 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG) Fri Nov 30 15:17:27 [rsStart] replSet can't get local.system.replset config from self or any seed (EMPTYCONFIG)

Right now both these nodes know that they are part of the “liverpool” replication set, but that is about it. They don’t know who else is part of the same replication set.

So when I connect to the mongod server on isvx7, it tells me that is not the master or the secondary.

[root@isvx7 ~]# mongo --port 27001 MongoDB shell version: 2.2.0 connecting to: 127.0.0.1:27001/test > db.isMaster() {         "ismaster" : false,         "secondary" : false,         "info" : "can't get local.system.replset config from self or any seed (EMPTYCONFIG)",         "isreplicaset" : true,         "maxBsonObjectSize" : 16777216,         "localTime" : ISODate("2012-11-30T23:22:44.236Z"),         "ok" : 1 } >

This means that I would need to run replSetInitiate to initiate the replication set on the nodes, but before that we need to create the config file on node isvx7.

> cfg = { _id : "liverpool", members : [ { _id:0, host:"isvx7:27001" }, { _id:1, host:"isvx3:27001" } ] } {         "_id" : "liverpool",         "members" : [                 {                         "_id" : 0,                         "host" : "isvx7:27001"                 },                 {                         "_id" : 1,                         "host" : "isvx3:27001"                 }         ] } >

Now we will initiate the replica set on node isvx7 with the config file that we created.

> rs.initiate(cfg) {         "info" : "Config now saved locally.  Should come online in about a minute.",         "ok" : 1 } >

When we now do the db.isMaster() on isvx7, we see that it is the master/primary.

> db.isMaster() {         "setName" : "liverpool",         "ismaster" : true,         "secondary" : false,         "hosts" : [                 "isvx7:27001",                 "isvx3:27001"         ],         "primary" : "isvx7:27001",         "me" : "isvx7:27001",         "maxBsonObjectSize" : 16777216,         "localTime" : ISODate("2012-11-30T23:51:11.561Z"),         "ok" : 1 } liverpool:PRIMARY>

Here is what I see when I try to start the shell from the secondary node.

[root@isvx3 ~]#  mongo --port 27001 MongoDB shell version: 2.2.0 connecting to: 127.0.0.1:27001/test Welcome to the MongoDB shell. For interactive help, type "help". For more comprehensive documentation, see         http://docs.mongodb.org/ Questions? Try the support group         http://groups.google.com/group/mongodb-user liverpool:SECONDARY> liverpool:SECONDARY> db.isMaster() {         "setName" : "liverpool",         "ismaster" : false,         "secondary" : true,         "hosts" : [                 "isvx3:27001",                 "isvx7:27001"         ],         "primary" : "isvx7:27001",         "me" : "isvx3:27001",         "maxBsonObjectSize" : 16777216,         "localTime" : ISODate("2012-12-01T00:03:49.245Z"),         "ok" : 1 } liverpool:SECONDARY>

Install and configure MongoDB on Linux

I decided to play around with MongoDB a bit, so I downloaded it from http://www.mongodb.org/downloads as follows

[root@isvx7 ~]# mkdir mongodb [root@isvx7 ~]# cd mongodb [root@isvx7 mongodb]# wget http://fastdl.mongodb.org/linux/mongodb-linux-x86_64-2.2.0.tgz --2012-10-26 11:15:58--  http://fastdl.mongodb.org/linux/mongodb-linux-x86_64-2.2.0.tgz Resolving fastdl.mongodb.org... 54.240.190.202, 54.240.190.201, 54.240.190.172, ... Connecting to fastdl.mongodb.org|54.240.190.202|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 56286069 (54M) [application/x-tar] Saving to: `mongodb-linux-x86_64-2.2.0.tgz' 100%[======================================>] 56,286,069  5.97M/s   in 9.3s 2012-10-26 11:16:07 (5.75 MB/s) - `mongodb-linux-x86_64-2.2.0.tgz' saved [56286069/56286069] [root@isvx7 mongodb]# [root@isvx7 mongodb]# gunzip mongodb-linux-x86_64-2.2.0.tgz [root@isvx7 mongodb]# ls mongodb-linux-x86_64-2.2.0.tar [root@isvx7 mongodb]# tar -xvf mongodb-linux-x86_64-2.2.0.tar mongodb-linux-x86_64-2.2.0/GNU-AGPL-3.0 mongodb-linux-x86_64-2.2.0/README mongodb-linux-x86_64-2.2.0/THIRD-PARTY-NOTICES mongodb-linux-x86_64-2.2.0/bin/mongodump mongodb-linux-x86_64-2.2.0/bin/mongorestore mongodb-linux-x86_64-2.2.0/bin/mongoexport mongodb-linux-x86_64-2.2.0/bin/mongoimport mongodb-linux-x86_64-2.2.0/bin/mongostat mongodb-linux-x86_64-2.2.0/bin/mongotop mongodb-linux-x86_64-2.2.0/bin/mongooplog mongodb-linux-x86_64-2.2.0/bin/mongofiles mongodb-linux-x86_64-2.2.0/bin/bsondump mongodb-linux-x86_64-2.2.0/bin/mongoperf mongodb-linux-x86_64-2.2.0/bin/mongosniff mongodb-linux-x86_64-2.2.0/bin/mongod mongodb-linux-x86_64-2.2.0/bin/mongos mongodb-linux-x86_64-2.2.0/bin/mongo [root@isvx7 mongodb]# ls mongodb-linux-x86_64-2.2.0  mongodb-linux-x86_64-2.2.0.tar [root@isvx7 mongodb]# cd mongodb-linux-x86_64-2.2.0 [root@isvx7 mongodb-linux-x86_64-2.2.0]# ls bin  GNU-AGPL-3.0  README  THIRD-PARTY-NOTICES [root@isvx7 mongodb-linux-x86_64-2.2.0]# ls -l total 56 drwxr-xr-x 2 root  root   4096 Oct 26 11:17 bin -rw------- 1 admin admin 34520 Aug 13 10:38 GNU-AGPL-3.0 -rw------- 1 admin admin  1359 Aug 13 10:38 README -rw------- 1 admin admin 11527 Aug 21 06:34 THIRD-PARTY-NOTICES [root@isvx7 mongodb-linux-x86_64-2.2.0]# cd bin [root@isvx7 bin]# ls bsondump  mongodump    mongoimport  mongorestore  mongostat mongo     mongoexport  mongooplog   mongos        mongotop mongod    mongofiles   mongoperf    mongosniff [root@isvx7 bin]#

By default mongodb uses /data/db for its datafiles. Below I check to see if I have enough space on / to create /data/db and have some files in it.

[root@isvx7 ~]# df -h / Filesystem            Size  Used Avail Use% Mounted on /dev/sda3             255G   76G  166G  32% / [root@isvx7 ~]# mkdir -p /data/db [root@isvx7 ~]#

Next, I start the server mongod, and strace it.

[root@isvx7 bin]# strace -o /root/output.txt ./mongod ./mongod --help for help and startup options Fri Oct 26 15:07:52 [initandlisten] MongoDB starting : pid=31518 port=27017 dbpath=/data/db/ 64-bit host=isvx7.storage.tucson.ibm.com Fri Oct 26 15:07:52 [initandlisten] Fri Oct 26 15:07:52 [initandlisten] ** WARNING: You are running on a NUMA machine. Fri Oct 26 15:07:52 [initandlisten] **          We suggest launching mongod like this to avoid performance problems: Fri Oct 26 15:07:52 [initandlisten] **              numactl --interleave=all mongod [other options] Fri Oct 26 15:07:52 [initandlisten] Fri Oct 26 15:07:52 [initandlisten] ** WARNING: /proc/sys/vm/zone_reclaim_mode is 1 Fri Oct 26 15:07:52 [initandlisten] **          We suggest setting it to 0 Fri Oct 26 15:07:52 [initandlisten] **          http://www.kernel.org/doc/Documentation/sysctl/vm.txt Fri Oct 26 15:07:52 [initandlisten] Fri Oct 26 15:07:52 [initandlisten] db version v2.2.0, pdfile version 4.5 Fri Oct 26 15:07:52 [initandlisten] git version: f5e83eae9cfbec7fb7a071321928f00d1b0c5207 Fri Oct 26 15:07:52 [initandlisten] build info: Linux ip-10-2-29-40 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_49 Fri Oct 26 15:07:52 [initandlisten] options: {} Fri Oct 26 15:07:52 [initandlisten] journal dir=/data/db/journal Fri Oct 26 15:07:52 [initandlisten] recover : no journal files present, no recovery needed Fri Oct 26 15:07:54 [initandlisten] preallocateIsFaster=true 28.32 Fri Oct 26 15:07:56 [initandlisten] preallocateIsFaster=true 27.74 Fri Oct 26 15:07:59 [initandlisten] preallocateIsFaster=true 30.82 Fri Oct 26 15:07:59 [initandlisten] preallocateIsFaster check took 7.423 secs Fri Oct 26 15:07:59 [initandlisten] preallocating a journal file /data/db/journal/prealloc.0 Fri Oct 26 15:08:11 [initandlisten] preallocating a journal file /data/db/journal/prealloc.1 Fri Oct 26 15:08:23 [initandlisten] preallocating a journal file /data/db/journal/prealloc.2 Fri Oct 26 15:08:36 [websvr] admin web console waiting for connections on port 28017 Fri Oct 26 15:08:36 [initandlisten] waiting for connections on port 27017

Here is what got created under /data/db

[root@isvx7 ~]# cd /data/db [root@isvx7 db]# ls journal  mongod.lock [root@isvx7 db]# ls -l total 8 drwxr-xr-x 2 root root 4096 Oct 26 15:08 journal -rwxr-xr-x 1 root root    6 Oct 26 15:07 mongod.lock [root@isvx7 db]# cd journal/ [root@isvx7 journal]# ls j._0  prealloc.1  prealloc.2 [root@isvx7 journal]# ls -lh total 3.1G -rw------- 1 root root 1.0G Oct 26 15:08 j._0 -rw------- 1 root root 1.0G Oct 26 15:08 prealloc.1 -rw------- 1 root root 1.0G Oct 26 15:08 prealloc.2 [root@isvx7 journal]#

Let us look into the output.txt to see the what happens when mongod is run.

• Here we see that it checks to see if /data/db directory is present, and then goes onto check if mongod.lock file is present. It see that it is not there, so it goes onto create a mongod.lock file and writes 31518 into it which is the process id of mongod ie. "root     31518 31517  0 15:07 pts/2    00:00:04 ./mongod"

write(1, "Fri Oct 26 15:07:52 [initandlist"..., 48) = 48 stat("/data/db/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 stat("/data/db/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 stat("/data/db/mongod.lock", 0x7fffc6e703b0) = -1 ENOENT (No such file or directory) open("/data/db/mongod.lock", O_RDWR|O_CREAT, 0777) = 4 flock(4, LOCK_EX|LOCK_NB)               = 0 ftruncate(4, 0)                         = 0 write(4, "31518\n", 6)                  = 6 fsync(4)                                = 0

• Here you see that it checks to see if /data/db/journal is present, and then goes onto check i

write(1, "Fri Oct 26 15:07:52 [initandlist"..., 65) = 65 stat("/data/db/journal", 0x7fffc6e704d0) = -1 ENOENT (No such file or directory) mkdir("/data/db/journal", 0777)         = 0 stat("/data/db/journal", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 open("/data/db/journal", O_RDONLY|O_NONBLOCK|O_DIRECTORY) = 5 fcntl(5, F_SETFD, FD_CLOEXEC)           = 0 getdents(5, /* 2 entries */, 32768)     = 48 getdents(5, /* 0 entries */, 32768)     = 0 close(5)                                = 0

• Here we see it checks to see if files prealloc.0, prealloc.1, and prealloc.2 are present.

stat("/data/db/journal/prealloc.0", 0x7fffc6e703f0) = -1 ENOENT (No such file or directory) stat("/data/db/journal/prealloc.1", 0x7fffc6e703f0) = -1 ENOENT (No such file or directory) stat("/data/db/journal/prealloc.2", 0x7fffc6e703f0) = -1 ENOENT (No such file or directory) stat("/data/db/journal/prealloc.0", 0x7fffc6e704f0) = -1 ENOENT (No such file or directory) stat("/data/db/journal/prealloc.1", 0x7fffc6e704f0) = -1 ENOENT (No such file or directory) stat("/data/db/journal/tempLatencyTest", 0x7fffc6e703c0) = -1 ENOENT (No such file or directory)

• Next it creates the tempLatencyTest file, and writes to it as shown below.

open("/data/db/journal/tempLatencyTest", O_WRONLY|O_CREAT|O_DIRECT|O_NOATIME, 0600) = 5 open("/data/db/journal", O_RDONLY)      = 6 fsync(6)                                = 0 close(6)                                = 0 lseek(5, 0, SEEK_CUR)                   = 0 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 lseek(5, 0, SEEK_CUR)                   = 8192 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 lseek(5, 0, SEEK_CUR)                   = 16384 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 ........................................................... ........................................................... ........................................................... lseek(5, 0, SEEK_CUR)                   = 393216 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 lseek(5, 0, SEEK_CUR)                   = 401408 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 close(5)                                = 0 open("/data/db/journal/tempLatencyTest", O_WRONLY|O_CREAT|O_DIRECT|O_NOATIME, 0600) = 5 open("/data/db/journal", O_RDONLY)      = 6 fsync(6)                                = 0 close(6)                                = 0 lseek(5, 0, SEEK_CUR)                   = 0 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 lseek(5, 0, SEEK_CUR)                   = 8192 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 lseek(5, 0, SEEK_CUR)                   = 16384 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 ........................................................... ........................................................... ........................................................... fdatasync(5)                            = 0 lseek(5, 0, SEEK_CUR)                   = 393216 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 lseek(5, 0, SEEK_CUR)                   = 401408 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192) = 8192 fdatasync(5)                            = 0 close(5)                                = 0

• Here we see that the tempLatencyTest file is deleted.

write(1, "Fri Oct 26 15:07:54 [initandlist"..., 67) = 67 stat("/data/db/journal/tempLatencyTest", {st_mode=S_IFREG|0600, st_size=409600, ...}) = 0 lstat("/data/db/journal/tempLatencyTest", {st_mode=S_IFREG|0600, st_size=409600, ...}) = 0 unlink("/data/db/journal/tempLatencyTest") = 0 stat("/data/db/journal/tempLatencyTest", 0x7fffc6e703c0) = -1 ENOENT (No such file or directory

• Next we see that the file prealloc.0 is created, and 1 MB is written into it using pwrite to create a totalof 1 GB. The same is repeated for file prealloc.1 and prealloc.2

"Prealloc Files (e.g. journal/prealloc.0)

mongod will create prealloc files in the journal directory under some circumstances to minimize journal write latency. On some filesystems, appending to a file and making it larger can be slower than writing to a file of a predefined size. mongod checks this at startup and if it finds this to be the case will use preallocated journal files. If found to be helpful, a small pool of prealloc files will be created in the journal directory before startup begins. This is a one time initiation and does not occur with future invocations. Approximately 3GB of files will be preallocated (and truly prewritten, not sparse allocated) - thus in this situation, expect roughly a 3 minute delay on the first startup to preallocate these files."
From MongoDb docs: http://www.mongodb.org/display/DOCS/Journaling+Administration+Notes#JournalingAdministrationNotes-PreallocFiles%28e.g.journal%2Fprealloc.0%29

open("/data/db/journal/prealloc.0", O_RDWR|O_CREAT|O_NOATIME, 0600) = 5 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 0) = 1048576 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 1048576) = 1048576 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 2097152) = 1048576 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 3145728) = 1048576 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 4194304) = 1048576 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 5242880) = 1048576 .............................................................. .............................................................. .............................................................. pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 1070596096) = 1048576 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 1071644672) = 1048576 pwrite(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 1072693248) = 1048576 fsync(5)                                = 0 close(5)                                = 0

• Here we see that it checks to see if file j._0 exists, and then goes onto rename file prealloc.0 to j._0

"Journal Files (e.g. journal/j._0)

Journal files are append-only and are written to the journal/ directory under the dbpath directory (which is /data/db/ by default).

Journal files are named j._0, j._1, etc. When a journal file reached 1GB in size, a new file is created. Old files which are no longer needed are rotated out (automatically deleted). Unless your write bytes/second rate is extremely high, you should have only two or three journal files.

Note: in more recent versions, the journal files are only 128MB apiece when using the --smallfiles command line option."
From MongoDb docs: http://www.mongodb.org/display/DOCS/Journaling+Administration+Notes#JournalingAdministrationNotes-PreallocFiles%28e.g.journal%2Fprealloc.0%29

stat("/data/db/journal/j._0", 0x7fffc6e6e350) = -1 ENOENT (No such file or directory) rename("/data/db/journal/prealloc.0", "/data/db/journal/j._0") = 0

• Here we see that the domain parameter for the socket() is PF_INET ie. IPv4 Internet protocol. SOCK_STREAM provides sequenced, reliable, two-way, connection-based byte streams. Also, we see that the port used is 27017

socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 7 setsockopt(7, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 bind(7, {sa_family=AF_INET, sin_port=htons(27017), sin_addr=inet_addr("0.0.0.0")}, 16) = 0 listen(7, 128)                          = 0 socket(PF_FILE, SOCK_STREAM, 0)         = 8 unlink("/tmp/mongodb-27017.sock")       = -1 ENOENT (No such file or directory) setsockopt(8, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 bind(8, {sa_family=AF_FILE, path="/tmp/mongodb-27017.sock"...}, 110) = 0 chmod("/tmp/mongodb-27017.sock", 0777)  = 0 listen(8, 128)                          = 0 write(1, "Fri Oct 26 15:08:36 [initandlist"..., 74) = 74