Which Lock In MongoDB Provides Concurrency?

Which of the following operations in MongoDB can lock more than 1 databases?

Answer: The following MongoDB operations lock multiple databases: db.

copyDatabase() must lock the entire mongod instance at once..

How much data can MongoDB handle?

MongoDB is happy to accommodate large documents of up to 16 MB in collections, and GridFS is designed for large documents over 16MB. Because large documents can be accommodated doesn’t mean that it is a good idea.

How does MongoDB cache work?

MongoDB keeps most recently used data in RAM. If you have created indexes for your queries and your working data set fits in RAM, MongoDB serves all queries from memory. MongoDB does not cache the query results in order to return the cached results for identical queries.

What is the disadvantage of locking?

Locking has a few other disadvantages. When a thread is waiting for a lock, it cannot do anything else. … If a thread holding a lock is permanently blocked (due to an infinite loop, deadlock, livelock, or other liveness failure), any threads waiting for that lock can never make progress.

How much RAM does MongoDB need?

approximately 1GBMongoDB requires approximately 1GB of RAM per 100.000 assets. If the system has to start swapping memory to disk, this will have a severely negative impact on performance, and should be avoided.

How make MongoDB faster?

7 Simple Speed Solutions for MongoDBCheck Your MongoDB Log. By default, MongoDB records all queries which take longer than 100 milliseconds. … Analyze Your Queries. … Add Appropriate Indexes. … Be Wary When Sorting. … Create Two or More Connection Objects. … Set Maximum Execution Times. … Rebuild Your Indexes.

What are the problems with concurrency?

Concurrency ProblemsLost Updates. This problem occurs when two transactions, accessing the same data items, have their operations interleaved in such a way, that one transaction will access the data before the other has applied any updates.Uncommitted Data. … Inconsistent Retrievals.

What is meant by concurrency?

Noun. (plural concurrencies) The property or an instance of being concurrent; something that happens at the same time as something else. (computer science) a property of systems where several processes execute at the same time.

How do I lock a collection in MongoDB?

MongoDB implements a writer greedy database level lock already. This means that when a specific document is being written to: The User collection would be locked. No reads will be available until the data is written.

Is MongoDB thread safe?

Thread Safety Not all of the MongoDB client classes are thread-safe – please refer to the documentation of your specific driver to check if the classes you’re using are thread-safe. For example, in the Java driver, the MongoClient class is thread-safe.

Which process in MongoDB provides high scalability?

MongoDB supports horizontal scaling through Sharding , distributing data across several machines and facilitating high throughput operations with large sets of data.

Which is the method used to check whether collection is capped or not?

isCapped() command is used to check if a collection is a Capped collection or not. Advantages of Capped Collections: 1. Queries do not need an index to return documents in insertion order due to which it provide higher insertion throughput.

How do I use findAndModify in MongoDB?

MongoDB findAndModify() method modifies and returns a single document based upon the selection criteria entered. The returned document does not show the updated content by default. If the records matching the criteria does not exist in the database, a new record will be inserted if the upsert is set to true.

What is Mongod lock?

Mongodb always creates the mongodb. lock file when the server starts and drops it before mongodb is stopped. Removing mongodb. lock does not affect any data it just means that mongodb was not stopped correctly. So, you are correct in removing this file and running with the -repair option should fix database.

How many concurrent requests can MongoDB handle?

Scaling Crittercism to 30,000 Requests Per Second and Beyond with MongoDB.

What is lock in concurrency control?

A lock is a data variable which is associated with a data item. This lock signifies that operations that can be performed on the data item. Locks help synchronize access to the database items by concurrent transactions. All lock requests are made to the concurrency-control manager.

Is MongoDB multithreaded?

MongoDB uses multi-granularity locking [1] that allows operations to lock at the global, database or collection level, and allows for individual storage engines to implement their own concurrency control below the collection level (e.g., at the document-level in WiredTiger).

Is MongoDB transactional?

In MongoDB 2.2, individual operations are Atomic. … By having per database locks and control reads and writes to collections, write operations on collections are Consistent and Isolated.

Which is the method used in MongoDB to grant user?

To add a user, MongoDB provides the db. createUser() method. When adding a user, you can assign roles to the user in order to grant privileges. The first user created in the database should be a user administrator who has the privileges to manage other users.

Is the method in MongoDB similar to SQL order by clause?

8. Which of the following method corresponds to Order by clause in SQL? Explanation: The sort() method orders the documents in the result set. … Explanation: limit() corresponds to the LIMIT statement in SQL.

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.