MongoDB: count() inconsistency during the MongoDB Initial Sharding
We observed that inconsistent document counts of a collection when we query thru mongos during initial sharding due to newly added shard to the existing set-up. It’s expected to have inconsistent counts when we query directly on shard, but App…
MongoDB: lock/unlock users
While there are no built in commands for lock/unLock, it is possible to add them. Here are a couple of simple implementations that remove the user you want to lock from the db.system.users collection and save it in a lockedUsers…
MongoDB User creation: localhost exception
If we create a user in Mongos (router), we can authenticate Mongod’s (RS/Shard: in case of shard, user should have ‘clusterAdmin’ role) using that user. But still we can directly connect to Mongod’s with localhost exception with out any UN/PW….
MongoDB ConfigDB differ issue – Recovery procedure
We have 3 config servers ( say config1, config2 & config3 ) in production and imagine we have config db differ issue (configdb mismatch) on the config1 & config3. Then we may have to follow the following procedure to recover…
MongoDB Custom script for Monitoring
Main PHP program ( mm.php ) :- [root@MyLabBox v8]# pwd /var/www/html/mongo/v8 [root@MyLabBox v8]# cat mm.php <?php ############################################################# ############################################################# header(‘Refresh:120’); include(“mm_data.php”); $data_cfg_file = “datanode.cfg”; $fd = fopen($data_cfg_file, ‘r’); $node=fgets($fd); $count=1; echo ” <tr>”; while ( $node != “”) { $out =…
MongoDB Shrink database for cleanup space released
When documents or collections are deleted, empty record blocks within data files arise. MongoDB attempts to reuse this space when possible, but it will never return this space to the file system. This behavior explains why fileSize never decreases despite…
Aggregation Framework Operators
Pipeline Operators :- NOTE The aggregation pipeline cannot operate on values of the following types: Symbol, MinKey, MaxKey,DBRef, Code, and CodeWScope. Pipeline operators appear in an array. Documents pass through the operators in a sequence. Name Description $project Reshapes a…
MongoDB High Availability Min configuration
If you have 1 Primary node, 1 Secondary node and 1 Arbiter, and you are using majority write, then you are requiring that the write be made on both the Primary and the Secondary. As soon as one of those…
MongoDB Aggregation Concepts
MongoDB provides the three approaches to aggregation, each with its own strengths and purposes for a given situation. This section describes these approaches and also describes behaviors and limitations specific to each approach. See also the chart that compares the…
password option file in MongoDB
if you’re curious to know whether we’ve password option file concept in MongoDB something similar to MySQL (refer below links). http://dev.mysql.com/doc/refman/5.1/en/password-security-user.html http://stackoverflow.com/questions/16299603/mysql-utilities-my-cnf-option-file With this, we can actually save credentials in a option hidden file within client session and we no…