What is Writeconcern?
Write concern describes the level of acknowledgment requested from MongoDB for write operations to a standalone mongod or to replica sets or to sharded clusters. In sharded clusters, mongos instances will pass the write concern on to the shards.
When should you set a Wtimeout?
wtimeout is only applicable for w values greater than 1 . wtimeout causes write operations to return with an error after the specified limit, even if the required write concern will eventually succeed.
What is read and write concern in MongoDB?
write concern. allows you to set the level of acknowledgment for a desired write operation. Likewise, the. read concern. allows you to control the consistency and isolation properties of the data read from your replica sets.
What is acknowledged in MongoDB?
Acknowledged MongoDB Mode This is the default write mode for MongoDB. In this mode, the MongoDB driver attempts to acknowledge the receipt of write operations on the server, allowing the driver to catch any network errors, duplicate keys errors, etc. However, this does not guarantee that data is saved on the disk.
Is MongoDB consistent?
By default, MongoDB is a strongly consistent system. Once a write completes, any subsequent read will return the most recent value. Cassandra, by default, is an eventually consistent system. Once a write completes, the latest data eventually becomes available provided no subsequent changes are made.
What is Journal MongoDB?
With journaling enabled, MongoDB writes the in-memory changes first to on-disk journal files. If MongoDB should terminate or encounter an error before committing the changes to the data files, MongoDB can use the journal files to apply the write operation to the data files and maintain a consistent state.
Is MongoDB strongly consistent?
What is MongoDB transaction?
For situations that require atomicity of reads and writes to multiple documents (in a single or multiple collections), MongoDB supports multi-document transactions. With distributed transactions, transactions can be used across multiple operations, collections, databases, documents, and shards.
How does MongoDB replica work?
MongoDB achieves replication by the use of replica set. A replica set is a group of mongod instances that host the same data set. In a replica, one node is primary node that receives all write operations. All other instances, such as secondaries, apply operations from the primary so that they have the same data set.
What is heartbeat in MongoDB?
Heartbeat is the process that identifies the current status of a MongoDB node in a replica set. There, the replica set nodes send pings to each other every two seconds (hence the name).
Is MongoDB online or offline?
MongoDB is an online Big Data technology that serves as an operational data store for today’s Big Data applications. The database also integrates well with many offline Big Data solutions so that you can come up with a complete data solution.
Is MongoDB ACID compliant?
MongoDB added support for multi-document ACID transactions in version 4.0 in 2018 and extended that support for distributed multi-document ACID transactions in version 4.2 in 2019. MongoDB’s document model allows related data to be stored together in a single document.
How does MongoDB journaling work?
MongoDB uses memory mapped files to write your data to disk. By default, MongoDB data files are flushed to disk every 60 seconds. They also uses memory mapped files for the journal, and by default, the journal is flushed to disk every 100ms.