MongoDB Sharding Overview
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Questions and Answers

What is the minimum size for records to be compressed in WiredTiger?

  • 128 bytes (correct)
  • 64 bytes
  • 256 bytes
  • 512 bytes

    • What is the maximum size limit for WiredTiger journal files?

  • 100 MB (correct)
  • 150 MB
  • 200 MB
  • 50 MB

    • What happens to older journal files in WiredTiger?

  • They are compressed to save space.
  • They are automatically removed after successful recovery. (correct)
  • They are permanently retained for historical analysis.
  • They are archived indefinitely.

    • Why does WiredTiger pre-allocate journal files?

    <p>To optimize performance.</p> Signup and view all the answers

    How should disk space for journal files in WiredTiger be estimated?

    <p>By overestimating space for safety.</p> Signup and view all the answers

    What command is used to initiate a replica set for a shard?

    <p>rs.initiate()</p> Signup and view all the answers

    Which of the following parameters must be included when starting a shard with mongod?

    <p>--shardsvr</p> Signup and view all the answers

    What method allows you to enable sharding for a specific database?

    <p>sh.enableSharding()</p> Signup and view all the answers

    When configuring a shard collection, which of the following sharding types equally distributes data across shards?

    <p>hashed sharding</p> Signup and view all the answers

    Which command is used to add a shard to the cluster?

    <p>addShard()</p> Signup and view all the answers

    What is the purpose of a journal in MongoDB's storage engine?

    <p>To recover data after a hard shutdown</p> Signup and view all the answers

    In the context of MongoDB, what does the command sh.shardCollection() do?

    <p>Enables sharding for a specified collection</p> Signup and view all the answers

    Which command should be omitted for initializing a replica set member while setting up a shard?

    <p>--configsvr</p> Signup and view all the answers

    What does a shard key do in MongoDB?

    <p>It is used to distribute documents across shards.</p> Signup and view all the answers

    What is the maximum size of each data chunk in MongoDB sharding?

    <p>128MB</p> Signup and view all the answers

    Which sharding strategy divides data into ranges based on shard key values?

    <p>Ranging Sharding</p> Signup and view all the answers

    What role does the balancer serve in MongoDB sharding?

    <p>To migrate data chunks and maintain equal data across shards.</p> Signup and view all the answers

    How many mongod processes can a configuration server replica set have at maximum?

    <p>50</p> Signup and view all the answers

    Which of the following describes hashed sharding?

    <p>It applies a hash to the shard key field's value.</p> Signup and view all the answers

    What is the purpose of zone sharding in MongoDB?

    <p>To separate data based on application requirements.</p> Signup and view all the answers

    What command is used to initiate the configuration server in a replica set?

    <p>rs.initiate()</p> Signup and view all the answers

    What is the primary advantage of using sharding in MongoDB?

    <p>Increased storage and processing capacity</p> Signup and view all the answers

    What role does the 'mongos' serve in a sharded cluster?

    <p>It connects client applications to the sharded cluster.</p> Signup and view all the answers

    Which of the following describes a shard in MongoDB?

    <p>A component of the sharded data that functions as a replica set.</p> Signup and view all the answers

    What is the function of config servers in a MongoDB sharded cluster?

    <p>To store cluster metadata and configuration parameters.</p> Signup and view all the answers

    Which scaling method allows adding more servers to handle increased workload in MongoDB?

    <p>Horizontal scaling</p> Signup and view all the answers

    How does sharding contribute to high availability in MongoDB?

    <p>By utilizing multiple servers for redundancy.</p> Signup and view all the answers

    What does zone sharding facilitate in a distributed database context?

    <p>Design for geographically dispersed applications.</p> Signup and view all the answers

    How much additional throughput does each shard add in MongoDB?

    <p>1,000 operations per second</p> Signup and view all the answers

    What is the default storage engine in MongoDB?

    <p>WiredTiger</p> Signup and view all the answers

    Which method does WiredTiger use to handle transaction concurrency?

    <p>Optimistic concurrency control</p> Signup and view all the answers

    How many read and write transactions can WiredTiger handle per node at maximum?

    <p>128 read and 128 write</p> Signup and view all the answers

    What is the purpose of snapshots in WiredTiger?

    <p>They provide consistent views of data at the start of operations.</p> Signup and view all the answers

    What is the frequency of checkpoints in WiredTiger?

    <p>Every 60 seconds</p> Signup and view all the answers

    Which compression method is employed for journal data in WiredTiger?

    <p>Snappy compression</p> Signup and view all the answers

    What happens to performance when WiredTiger encounters heavy write workloads?

    <p>Performance may degrade.</p> Signup and view all the answers

    What is a characteristic of document-level concurrency in WiredTiger?

    <p>It allows clients to write to different documents simultaneously.</p> Signup and view all the answers

    Study Notes

    MongoDB Sharding

    • Allows horizontal scaling for large workloads and data sets
    • Employs a shared-nothing architecture, where nodes don't share resources
    • Data is divided into shards, each functioning as a replica set for redundancy and availability
    • Shards handle specific workloads, and partitions can be added or removed based on demand

    Two Methods of Addressing System Growth

    • Vertical Scaling: Expanding the capacity of a single server by upgrading CPU, RAM, and storage space
    • Horizontal Scaling: Distributing the system's dataset and load across multiple servers, adding more servers as needed

    Sharded Cluster Components

    • Shard: Component of the sharded data, deployed as a replica set
    • Mongos: Serves as a query router, connecting client applications to the sharded cluster
    • Config Servers: Store cluster metadata and configuration parameters, must be a replica set (CSRS)

    MongoDB Sharding Benefits

    • Increased Read/Write Throughput: Achieved by distributing the data across multiple shards, allowing parallel processing. Example: Each shard can process 1,000 operations per second.
    • Increased Storage Capacity: Adding a shard increases the total storage capacity. Example: If one shard is 4TB, adding another increases capacity by an additional 4TB.
    • High Availability: Replica sets are essential for sharding, improving data availability by utilizing multiple servers.
    • Data Locality: Zone sharding facilitates the design of distributed databases for geographically dispersed applications, supporting data residency in specific regions.

    MongoDB Sharding Data Distribution

    • Shard Key: Used to distribute a collection's documents across shards. Data is partitioned into non-overlapping intervals based on shard key values.
    • Data Chunk Size: Maximum size of each data chunk is 128MB.
    • Balancer: A background function that automatically migrates data chunks between shards to ensure equal data distribution.

    Sharding Strategies

    • Ranging Sharding: Divides data into ranges based on shard key values. Shard keys with similar values are likely to be stored in the same chunk, enabling focused operations.
    • Hashed Sharding: Creates a hash of the shard key field's value. Data chunks are assigned ranges based on hashed shard key values, ensuring even data spread across shards.
    • Zone Sharding: Separates data into distinct zones based on application requirements. Each zone can be associated with one or more shards and can store data from multiple zones.

    How to Create a Sharded Collection in MongoDB

    • Step 1: Set up Config Servers:

      • Start each configuration server replica set member with the --configsvr option.
      • Link to one of the replica set members using mongosh.
      • Use rs.initiate() on one of the replica set members to initialize the replica set.

    • Step 2: Set up Shards:

      • Start each shard replica set member with the --shardsvr option and a unique replica set name.
      • Link to one of the replica set members using mongosh.
      • Use rs.initiate() on one of the replica set members, excluding the --configsvr option.

    • Step 3: Start Mongos:

      • Configure Mongos and point it to the configuration server replica set using mongos --configdb.

    • Step 4: Configure and Enable Sharding:

      • Connect to Mongos using mongosh.
      • Add shards to the cluster using sh.addShard().
      • Enable sharding for the database using sh.enableSharding().
      • Shard the collection with the sh.shardCollection() method. Choose between hashed sharding for even data distribution or range-based sharding for optimized distribution based on shard key values.

    MongoDB Storage Systems

    • Storage Engine: The primary component responsible for managing data.
    • GridFS for Self-Managed Deployments: A storage system for handling files exceeding the 16MB document size limit.
    • Journal: A write-ahead log system with checkpoints for data recovery after a shutdown.

    WiredTiger Storage Engine

    • Default Engine: Automatically selected unless otherwise specified. Supported in all MongoDB deployments.
    • Operation & Limitations:
      • Uses optimistic concurrency control.
      • Transaction concurrency is dynamically optimized, with a limit of 128 read and 128 write transactions per node.
      • WiredTiger cache isn't partitioned, potentially degrading performance under heavy write workloads.
    • Document Level Concurrency: Uses MultiVersion Concurrency Control (MVCC), allowing multiple clients to write to different documents simultaneously.
    • Snapshots & Checkpoints: Snapshots provide consistent views of data at the start of operations. Checkpoints ensure data durability by writing consistent snapshots to disk every 60 seconds.
    • Journal & Compression:
      • Journal persists all data modifications between checkpoints and uses compression by default.
      • Compression minimizes storage space, but requires additional CPU usage.
      • WiredTiger uses block compression for collections and prefix compression for indexes.
    • Journal File Size Limit: Maximum journal file size is 100MB. Older files are automatically removed after recovery.

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    Group 4 Replication, Sharding, & Storage.pdf

    Description

    This quiz covers the fundamental concepts of MongoDB sharding, including its architecture, scaling methods, and key components like shards, mongos, and config servers. Learn how sharding enhances data management and improves read/write throughput in large workloads.

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