When the Shard is slow, the query returns an error until partial query options are fixed. When the shard is reacting slowly, MongoDB waits for it.
Posted Date:- 2021-08-31 08:37:21
In MongoDB, we cannot configure the cache. MongoDB utilizes the free spaces over the system automatically by using memory-mapped files.
Posted Date:- 2021-08-31 08:36:39
From MongoDB3.2, we can perform the Join operation. The new $lookup operator included with the aggregation pipeline is the same as the left outer join. Example:
{
$lookup:
{
from: <collection to join>,
localField: <field from the input documents>,
foreignField: <field from the documents of the "from" collection>,
as: <output array field>
}
}
Posted Date:- 2021-08-31 08:35:53
No, MongoDB does not require plenty of RAM. It can run on a small amount of memory. MongoDB dynamically assigns and unassigns RAM according to the needs of other processes.
Posted Date:- 2021-08-31 08:35:06
Following are the elements of the Sharded Cluster:
1. Query routers
2. Shards
3. Config servers
Posted Date:- 2021-08-31 08:34:01
<> Vertical Scaling: Vertical Scaling increases storage and CPU resources for expanding the capacity.
<> Horizontal Scaling: Horizontal Scaling splits the datasets and circulates the data over multiple shards or servers.
Posted Date:- 2021-08-31 08:32:57
ObjectId contains the following:
1. Client machine ID
2. Client process ID
3. Byte incremented counter
4. Timestamp
Posted Date:- 2021-08-31 08:32:07
We must consider the following points while creating a schema:
< Designing the Scheme based on the user requirements.
< Combining the objects into one document, if we have to use them jointly, or else, separate them.
< Perform joins while on write, and not while it is on reading.
< For most general application scenarios, maximize the schema.
< Perform complex aggregations in the schema.
Posted Date:- 2021-08-31 08:30:57
We use the pretty() method for displaying the results in a formatted way.
Posted Date:- 2021-08-31 08:28:27
We use the “DB.drop database†command for dropping a database.
Posted Date:- 2021-08-31 08:27:38
Current database is referred to as ‘db’. Example – db.collection.find();
Posted Date:- 2021-08-31 08:26:57
To start a MongoDB instance, follow the steps as below:
> First, open the command prompt and run mongod.exe.
> Alternatively, you can move to the path where MongoDB is installed, for example, “C: MongoDBâ€
> Navigate to the bin folder, locate the mongod.exe and double click the same to execute it.
> You can also navigate to the required folder, for example, “C: MongoDB/bin†and type mongo to connect MongoDB through the shell.
Posted Date:- 2021-08-31 08:26:10
We use the mongodump command for creating the database backup.
Posted Date:- 2021-08-31 08:24:56
skip() method syntax is:
db.COLLECTION_NAME.find().limit(NUMBER).skip(NUMBER)
Posted Date:- 2021-08-31 08:24:17
When I want to create a database in MongoDB, I faced the following error:
:~$mongo
MongoDB shell version:1.65
Connecting to: test
Error: Could not connect to the server
Exception: connect failed
The solution to the above error:
cd/var1/lib1/MongoDB
We remove the mongod. lock from the folder
Sudo start MongoDB
Mongo
Posted Date:- 2021-08-31 08:22:59
Operational log(oplog) is a special kind of limited collection that stores a rolling record of all the operations which change the data we store in our databases. Primarily, it applies all the database operations over the primary and, after that, records these operations on the oplog of the primary. After that, the secondary members replicate and apply the operations in the asynchronous process.
Posted Date:- 2021-08-31 08:22:22
For finding any data in MongoDB, we use the find() method. The discovery () method returns the collection’s documents over which we invoked this method. We can use the “Where†clause in the MongoDB query in order to restrict the output by using MongoDB projection. Anytime we execute the find() method, MongoDB returns all the documents associated with a particular collection.
db.<collection_name>.find({ }, {<key_Name>:<Flag to display>})
Posted Date:- 2021-08-31 08:20:14
A secondary is a node/member that uses the existing primary’s operations. This is accomplished by following the replication oplog (local.oplog.rs). The replication from primary to secondary is asynchronous; however, the secondary will strive to keep up with the primary as much as practicable (on a LAN, this is often a few milliseconds).
Posted Date:- 2021-08-31 08:19:40
MongoDB maintains data integrity by creating an on-disk journal for each write. In the event of a server failure, the log will be used to detect writes that were not written to the disk or data files.
Posted Date:- 2021-08-31 08:18:59
Since the index contains all of the fields, MongoDB will fit the question condition and return the result fields without having to search into the documents. Since indexes are contained in RAM or sequentially on disk, such access is much quicker.
Posted Date:- 2021-08-31 08:15:52
No, it does not. By default, disk writes are lazy. A write cannot reach the disk for many seconds. For example, if the database receives a thousand increments to an object in one second, the object can only be flushed to disk once (it should be noted that fsync options are accessible both at the command line and via getLastError_old).
Posted Date:- 2021-08-31 08:14:49
It is made up of the following components:
1. Client process ID
2. Timestamp
3. Client machine ID
4. Byte incremented counter
Posted Date:- 2021-08-31 08:14:17
We use the “DB†command to get the name of the presently selected database.
Posted Date:- 2021-08-31 08:13:08
We use the save() method for replacing the existing documents with new documents.
Posted Date:- 2021-08-31 08:12:39
Splitting is the background process that we use to store chunks from increasing too large.
Posted Date:- 2021-08-31 08:12:08
No, MongoDB doesn’t support foreign key constraints. Because of the document structure, MongoDB provides flexible ways to define relationships.
Posted Date:- 2021-08-31 08:11:38
Use the command mongodump to create a backup.
Use the command mongorestore [backup_path] to restore the data.
Posted Date:- 2021-08-31 08:11:06
MongoDB contains the database profiler that shows the performance characteristics of every operation against the database. Through the profiler, we can identify the queries that are slower than they should be and use this data to determine when we require an index.
Posted Date:- 2021-08-31 08:10:34
a) Aggregation: Aggregations are the activities that handle the data records and give the record results.
b) Sharding: Sharding means storing the data on multiple machines.
Posted Date:- 2021-08-31 08:10:12
MongoDB utilizes the reader-writer locks, enabling concurrent readers to access any supply such as collection or database though it provides private access to individual writers.
Posted Date:- 2021-08-31 08:09:38
We save the write operations in the memory while journaling is taking place. The on-disk journal files are dependable for the reason that journal writers are usual. In the DB path, MongoDB designs a journal subdirectory.
Posted Date:- 2021-08-31 08:09:11
MongoDB does not use traditional locking with the reduction because it is high-speed, knowable, and light in the presentation. We can consider it as the MyISAM, MySQL auto entrust script. Through the simpler business sustain, we can enhance the performance, specifically in the structure with various servers.
Posted Date:- 2021-08-31 08:08:44
1. GridFS: We use GridFS to retrieve and store large files like images, videos, and audio files.
2. Journaling: We use Journaling for secure backups in MongoDB.
Posted Date:- 2021-08-31 08:08:11
Starting with MongoDB 3.2, you can add a document validator to collections. Unique indexes can also be formed using db.collection. createIndex(“keyâ€: 1, );
Posted Date:- 2021-08-31 08:07:17
The following points must be considered:
> Create the schema in accordance with the needs of the users.
> If you use several objects together, combine them into a single document. Separate them if necessary.
> Do joins while writing, not while reading.
> Optimize the schema with the most common use cases.
> In the schema, perform complex aggregation.
Posted Date:- 2021-08-31 08:06:58
MongoDB is written and coded in C++.
Posted Date:- 2021-08-31 08:06:14
While MongoDB, Couchbase and Couchbase DB have several similarities, they vary in terms of model execution requirements, crossing points, storage, duplications and so on.
Posted Date:- 2021-08-31 08:05:56
Yes, it’s only for the members of an object. Since a null is not an object, it cannot be attached to the database collection. However, {} can be added.
Posted Date:- 2021-08-31 08:05:38
The following command needs to be used: db._adminCommand(“connPoolStatsâ€);
Posted Date:- 2021-08-31 07:48:57
Applications can access real-time data changes using Change streams which acts as a subscriber to all the collection operations like insert, delete and update.
Posted Date:- 2021-08-31 07:46:06
The process of synchronizing data through several servers is known as replication. With several copies of data on various database servers, it offers continuity and increases data efficiency. Replication protects the database from the loss of a single server.
Posted Date:- 2021-08-31 07:45:42
False. All write operations are only performed on the master. Read operations, on the other hand, may be performed on any instance — slave or master. As more slaves are added to a replica set, only reads get faster.
Posted Date:- 2021-08-31 07:45:13
No, it does not. MongoDB does not need a ton of RAM to operate. It can operate on very little RAM because it dynamically allocates and deallocates RAM based on the needs of the processes.
Posted Date:- 2021-08-31 07:43:55
MongoDB scrap stands on a collection. As a result, an album containing all substances is stored in the form of a lump or mass. Where an extra time period is available there can be more than a few slice data accomplishment options, so when there is more than one chunk, data is extended to a large number of slices and can be extended to 64 MB.
Posted Date:- 2021-08-31 07:43:38
Yes, you can erase the attribute and then re-save() the object.
*Basic MongoDB interview questions like these are quite frequently asked to test the basic knowledge of the candidate.
Posted Date:- 2021-08-31 07:43:16
In MongoDB, the _id field is reserved for the primary key, and it has a unique value. If you don’t specify anything for _id, it will be filled with “MongoDB Id Object.†However, you can enter some unique information in that field.
Posted Date:- 2021-08-31 07:42:55
Since JSON is a schema-free data system, it will be more accurate to assume that MongoDB has a dynamically typed schema. Create and insert a text to begin creating a schema. When a document is entered into the database, a corresponding collection is generated.
Posted Date:- 2021-08-31 07:40:35
Some data types are Numbers, String, Array, Binary data, Boolean, Date, Regular expressions, ObjectId, etc…
Posted Date:- 2021-08-31 07:40:16
By embedding one document within another, we may achieve a primary key-foreign key relationship. For instance, an address document may be inserted inside a customer document.
Posted Date:- 2021-08-31 07:39:40
JSON (JavaScript Object Notation), like XML, is a human-readable data exchange standard. JSON has been the most commonly adopted data exchange standard on the web. JSON accepts booleans, numbers, sequences and arrays as data types. BSON, on the other hand, is the binary encoding used by MongoDB to store its documents. It is equivalent to JSON, but it expands JSON to accept additional data types, such as Date. Unlike JSON records, BSON documents are ordered. BSON usually uses less room than JSON and traverses easier. Since it is binary, BSON is, therefore, faster to encrypt and decode.
Posted Date:- 2021-08-31 07:39:03