Ans: Mongo-DB is a record database which gives superior, high accessibility and simple adaptability.
Ans:
Ans: A copy set is a group of mongo examples that host similar data index. In replica set, one hub is essential, and another is auxiliary. From essential to the secondary hub all information replicates.
Ans: Over different servers, the way toward synchronizing information is known as replication. It gives excess and increment information accessibility with various duplicates of information on various database servers. Replication helps in shielding the database from the departure of a solitary server.
Ans: MongoDB stores BSON (Binary Interchange and Structure Object Notation) objects in the collection. The link of the collection name and database name is known as a namespace.
Ans: The system of storing data records over different machines is known as Sharding. It is a MongoDB way to deal with the requests of data development. It is the flat segment of data in a database or search engine. Each partition is referred as shard or database shard.
Ans: To see the association utilized by Mongos utilize db_adminCommand (“connPoolStats”);
Ans: No. Writes to disk are lazy by default. A write may only hit the disk a couple of seconds later. For example, if the database receives thousand increments to an object within one second, it will only be flushed to disk once. (Note: fsync options are available both at the command line and via getLastError_old.)
Ans: MongoDB does not use traditional locking or complex transactions with rollback, as it is designed to be light weight, fast and predictable in its performance. It can be thought of how analogous is to the MySQL’s MyISAM autocommit model. By keeping transaction support extremely simple, performance is enhanced, especially in a system that may run across many servers.
Ans: MongoDB does aggressive preallocation of reserved space to avoid file system fragmentation.
Ans: Yes!
Ans: Yes!
Ans: There is an extra memory mapped file activity with journaling. This will further constrain the limited db size of 32-bit builds. For now, journaling by default is disabled on 32-bit systems.
Ans: Each journal (group) write is consistent and won’t be replayed during recovery unless it is complete.
Ans: Yes, but only for the members of an object. A null cannot be added to the database collection as it isn’t an object. But {}can be added.
Ans: No. If ‘getLastError’ (aka ‘Safe Mode’) is not called, the server does exactly behave the way as if it has been called. The ‘getLastError’ call simply allows one to get a confirmation that the write operation was successfully committed. Of course, often you will want that confirmation, but the safety of the write and its durability is independent.
Ans: We suggest starting with Non-Sharded for simplicity and quick startup, unless your initial data set will not fit on single servers. Upgrading to Sharded from Non-sharded is easy and seamless, so there is not a lot of advantage in setting up Sharding before your data set is large.
Ans: MongoDB includes a database profiler which shows performance characteristics of each operation against the database. With this profiler you can find queries (and write operations) which are slower than they should be and use this information for determining when an index is needed.
Ans: Yes, you can remove the attribute and then re-save() the object.
Ans: It may take 10-30 seconds for the primary to be declared down by the other members and a new primary to be elected. During this window of time, the cluster is down for primary operations i.e writes and strong consistent reads. However, eventually consistent queries may be executed to secondaries at any time (in slaveOk mode), including during this window.
Ans: This is a node/member which is currently the primary and processes all writes for the replica set. During a failover event in a replica set, a different member can become primary.
Ans: A secondary is a node/member which applies operations from the current primary. This is done by tailing the replication oplog (local.oplog.rs). Replication from primary to secondary is asynchronous, however, the secondary will try to stay as close to current as possible (often this is just a few milliseconds on a LAN).
Ans: Each Shard is a logical collection of partitioned data. The shard could consist of a single server or a cluster of replicas. Using a replica set for each Shard is highly recommended.
Ans: MongoDB Sharding is range-based. So all the objects in a collection lie into a chunk. Only when there is more than 1 chunk there is an option for multiple Shards to get data. Right now, the default chunk size is 64mb, so you need at least 64mb for migration.
Ans: The update will go through immediately on the old Shard and then the change will be replicated to the new Shard before ownership transfers.
Ans: If a Shard is down, the query will return an error unless the ‘Partial’ query options is set. If a shard is responding slowly, Mongos will wait for it.
Ans: Yes, these files are made as backups during normal Shard balancing operations. Once the operations are done then they can be deleted. The clean-up process is currently manual so this needs to be taken care of to free up space.
Ans: The following command needs to be used: db._adminCommand(“connPoolStats”);
Ans:
Ans: To inspect a source code of a function, without any parentheses, the function must be invoked.