15. MongoDB : MongoDB Performance

15. MongoDB : MongoDB Performance

Commands to check STATS ###########################################

//execute below command from bin , before that u should have started mongod
//below files exist in bin folder
mongostat;   //check statistics
mongotop; // to track all read and write activity


db.serverStatus(); 
db.stats();    //number of collection, objects etc..
db.items.stats();  //collection level statistics

Journaling Mechanics ###########################################

- If we launch MongoD in Journal mode, then all write 1st goes to Journal before it goes to DB
     -- mongod.exe --dbpath D:\mongoDBDatabase --rest --journal
- Adv : fast and cheap (eg: while writing if server goes down, then when ever server comes up it takes from journal later)

Storage Engines ###########################################

1> memory map1 - read heavy operation , this is based on m-map files.
2> Wired-Tiger - heavy write operation, eg: facebook, twitter etc.
               - complex - updates possible
               - Uses commit chckpoint - after every 60 secs moving data from Journal to memory

Index - UnderIndex/OverIndex - poor design ###########################################

- All indexes are written to RAM, only if RAM is full then it writes to Harddisc which is very slow.
- Usually - in production 10% of Harddisck RAM shoud be there
  Eg: 500 GB HD,  50G GB RAM

Mongoos ###########################################

- Always use Mongoos tool - which handles all connection pool internally

Backup data ###########################################

- 1> copy paste all collections which is inside "D://mongoDBDatabase"   all "wt" files.
     always enable journal if you need backup
- 2> mongodump    //reads data from a mongDB database and creates BSON files. (it takes only documents as backup, it wont take index's, takes what index on what field)
     mongorestore   //

Lock DB during backup ###########################################

- use admin
- db.runCommand({"fsync":1, "lock":1});   //lock during backup

- db.$cmd.sys.unlock.findOne();    //unlock after backup is done.