AWS Redshift Advanced

AWS Redshift Advanced

AWS Redshift Advanced topics cover Distribution Styles for table, Workload Management etc.

Distribution Styles

  • Table distribution style determines how data is distributed across compute nodes and helps minimize the impact of the redistribution step by locating the data where it needs to be before the query is executed.
  • Redshift supports four distribution styles; AUTO, EVEN, KEY, or ALL.

KEY distribution

  • A single column acts as distribution key (DISTKEY) and helps place matching values on the same node slice.
  • As a rule of thumb you should choose a column that:
    • Is uniformly distributed – Otherwise skew data will cause unbalances in the volume of data that will be stored in each compute node leading to undesired situations where some slices will process bigger amounts of data than others and causing bottlenecks.
    • acts as a JOIN column – for tables related with dimensions tables (star-schema), it is better to choose as DISTKEY the field that acts as the JOIN field with the larger dimension table, so that matching values from the common columns are physically stored together, reducing the amount of data that needs to be broadcasted through the network.

EVEN distribution

  • distributes the rows across the slices in a round-robin fashion, regardless of the values in any particular column
  • Choose EVEN distribution
    • when the table does not participate in joins
    • when there is not a clear choice between KEY and ALL distribution.

ALL distribution

  • whole table is replicated in every compute node.
  • ensures that every row is collocated for every join that the table participates in
  • ideal for for relatively slow moving tables, tables that are not updated frequently or extensively
  • Small dimension tables DO NOT benefit significantly from ALL distribution, because the cost of redistribution is low.

AUTO distribution

  • Redshift assigns an optimal distribution style based on the size of the table data for e.g. apply ALL distribution for a small table and as it grows changes it to Even distribution
  • Amazon Redshift applies AUTO distribution, be default.

Sort Key

  • Sort keys define the order data in which the data will be stored.
  • Sorting enables efficient handling of range-restricted predicates
  • Only one sort key per table can be defined, but it can be composed with one or more columns.
  • Redshift stores columnar data in 1 MB disk blocks. The min and max values for each block are stored as part of the metadata. If query uses a range-restricted predicate, the query processor can use the min and max values to rapidly skip over large numbers of blocks during table scans
  • The are two kinds of sort keys in Redshift: Compound and Interleaved.

Compound Keys

  • A compound key is made up of all of the columns listed in the sort key definition, in the order they are listed.
  • A compound sort key is more efficient when query predicates use a prefix, or query’s filter applies conditions, such as filters and joins, which is a subset of the sort key columns in order.
  • Compound sort keys might speed up joins, GROUP BY and ORDER BY operations, and window functions that use PARTITION BY and ORDER BY.

Interleaved Sort Keys

  • An interleaved sort key gives equal weight to each column in the sort key, so query predicates can use any subset of the columns that make up the sort key, in any order.
  • An interleaved sort key is more efficient when multiple queries use different columns for filters
  • Don’t use an interleaved sort key on columns with monotonically increasing attributes, such as identity columns, dates, or timestamps.
  • Use cases involve performing ad-hoc multi-dimensional analytics, which often requires pivoting, filtering and grouping data using different columns as query dimensions.

Constraints

  • Redshift supports UNIQUE, PRIMARY KEY and FOREIGN KEY constraints, however they are only with informational purposes.
  • Redshift does not perform integrity checks for these constraints and are used by query planner, as hints, in order to optimize executions.
  • Redshift does enforce NOT NULL column constraints.

Redshift Workload Management

  • Redshift workload management (WLM) enables users to flexibly manage priorities within workloads so that short, fast-running queries won’t get stuck in queues behind long-running queries
  • Redshift provides query queues, in order to manage concurrency and resource planning. Each queue can be configured with the following parameters:
    • Slots: number of concurrent queries that can be executed in this queue.
    • Working memory: percentage of memory assigned to this queue.
    • Max. Execution Time: the amount of time a query is allowed to run before it is terminated.
  • Queries can be routed to different queues using Query Groups and User Groups. As a rule of thumb, is considered a best practice to have separate queues for long running resource-intensive queries and fast queries that don’t require big amounts of memory and CPU.
  • By default, Amazon Redshift configures one queue with a concurrency level of five, which enables up to five queries to run concurrently, plus one predefined Superuser queue, with a concurrency level of one. A maximum of eight queues can be defined, with each queue configured with a maximum concurrency level of 50. The maximum total concurrency level for all user-defined queues (not including the Superuser queue) is 50.

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AWS Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.
  1. A Redshift data warehouse has different user teams that need to query the same table with very different query types. These user teams are experiencing poor performance. Which action improves performance for the user teams in this situation?
    1. Create custom table views.
    2. Add interleaved sort keys per team.
    3. Maintain team-specific copies of the table.
    4. Add support for workload management queue hopping.

AWS Redshift – Certification

AWS Redshift

  • Amazon Redshift is a fully managed, fast and powerful, petabyte scale data warehouse service
  • Redshift automatically helps
    • set up, operate, and scale a data warehouse, from provisioning the infrastructure capacity
    • patches and backs up the data warehouse, storing the backups for a user-defined retention period
    • monitors the nodes and drives to help recovery from failures
    • significantly lowers the cost of a data warehouse, but also makes it easy to analyze large amounts of data very quickly
    • provide fast querying capabilities over structured data using familiar SQL-based clients and business intelligence (BI) tools using standard ODBC and JDBC connections.
    • uses replication and continuous backups to enhance availability and improve data durability and can automatically recover from node and component failures.
    • scale up or down with a few clicks in the AWS Management Console or with a single API call
    • distribute & parallelize queries across multiple physical resources
    • supports VPC, SSL, AES-256 encryption and Hardware Security Modules (HSMs) to protect the data in transit and at rest.
  • Redshift only supports Single-AZ deployments and the nodes are available within the same AZ, if the AZ supports Redshift clusters
  • Redshift provides monitoring using CloudWatch and metrics for compute utilization, storage utilization, and read/write traffic to the cluster are available with the ability to add user-defined custom metrics
  • Redshift provides Audit logging and AWS CloudTrail integration
  • Redshift can be easily enabled to a second region for disaster recovery.

Redshift Architecture

Redshift Performance

  • Massively Parallel Processing (MPP)
    • automatically distributes data and query load across all nodes.
    • makes it easy to add nodes to the data warehouse and enables fast query performance as the data warehouse grows.
  • Columnar Data Storage
    • organizes the data by column, as column-based systems are ideal for data warehousing and analytics, where queries often involve aggregates performed over large data sets
    • columnar data is stored sequentially on the storage media, and require far fewer I/Os, greatly improving query performance
  • Advance Compression
    • Columnar data stores can be compressed much more than row-based data stores because similar data is stored sequentially on disk.
    • employs multiple compression techniques and can often achieve significant compression relative to traditional relational data stores.
    • doesn’t require indexes or materialized views and so uses less space than traditional relational database systems.
    • automatically samples the data and selects the most appropriate compression scheme, when the data is loaded into an empty table

Redshift Single vs Multi-Node Cluster

  • Single Node
    • single node configuration enables getting started quickly and cost-effectively & scale up to a multi-node configuration as the needs grow
  • Multi-Node
    • Multi-node configuration requires a leader node that manages client connections and receives queries, and two or more compute nodes that store data and perform queries and computations.
    • Leader node
      • provisioned automatically and not charged for
      • receives queries from client applications, parses the queries and develops execution plans, which are an ordered set of steps to process these queries.
      • coordinates the parallel execution of these plans with the compute nodes, aggregates the intermediate results from these nodes and finally returns the results back to the client applications.
    • Compute node
      • can contain from 1-128 compute nodes, depending on the node type
      • executes the steps specified in the execution plans and transmit data among themselves to serve these queries.
      • intermediate results are sent back to the leader node for aggregation before being sent back to the client applications.
      • supports Dense Storage or Dense Compute nodes (DC) instance type
        • Dense Storage (DS) allow creation of very large data warehouses using hard disk drives (HDDs) for a very low price point
        • Dense Compute (DC) allow creation of very high performance data warehouses using fast CPUs, large amounts of RAM and solid-state disks (SSDs)
      • direct access to compute nodes is not allowed

Redshift Availability & Durability

  • Redshift replicates the data within the data warehouse cluster and continuously backs up the data to S3 (11 9’s durability)
  • Redshift mirrors each drive’s data to other nodes within the cluster.
  • Redshift will automatically detect and replace a failed drive or node
  • If a drive fails, Redshift
    • cluster will remain available in the event of a drive failure
    • the queries will continue with a slight latency increase while Redshift rebuilds the drive from replica of the data on that drive which is stored on other drives within that node
    • single node clusters do not support data replication and the cluster needs to be restored from snapshot on S3
  • In case of node failure(s), Redshift
    • automatically provisions new node(s) and begins restoring data from other drives within the cluster or from S3
    • prioritizes restoring the most frequently queried data so the most frequently executed queries will become performant quickly
    • cluster will be unavailable for queries and updates until a replacement node is provisioned and added to the cluster
  • In case of Redshift cluster AZ goes down, Redshift
    • cluster is unavailable until power and network access to the AZ are restored
    • cluster’s data is preserved and can be used once AZ becomes available
    • cluster can be restored from any existing snapshots to a new AZ within the same region

Redshift Backup & Restore

  • Redshift replicates all the data within the data warehouse cluster when it is loaded and also continuously backs up the data to S3
  • Redshift always attempts to maintain at least three copies of the data
  • Redshift enables automated backups of the data warehouse cluster with a 1-day retention period, by default, which can be extended to max 35 days
  • Automated backups can be turned off by setting the retention period as 0
  • Redshift can also asynchronously replicate the snapshots to S3 in another region for disaster recovery

Redshift Scalability

  • Redshift allows scaling of the cluster either by
    • increasing the node instance type (Vertical scaling)
    • increasing the number of nodes (Horizontal scaling)
  • Redshift scaling changes are usually applied during the maintenance window or can be applied immediately
  • Redshift scaling process
    • existing cluster remains available for read operations only while a new data warehouse cluster gets created during scaling operations
    • data from the compute nodes in the existing data warehouse cluster is moved in parallel to the compute nodes in the new cluster
    • when the new data warehouse cluster is ready, the existing cluster will be temporarily unavailable while the canonical name record of the existing cluster is flipped to point to the new data warehouse cluster

Redshift vs EMR vs RDS

  • RDS is ideal for
    • structured data and running traditional relational databases while offloading database administration
    • for online-transaction processing (OLTP) and for reporting and analysis
  • Redshift is ideal for
    • large volumes of structured data that needs to be persisted and queried using standard SQL and existing BI tools
    • analytic and reporting workloads against very large data sets by harnessing the scale and resources of multiple nodes and using a variety of optimizations to provide improvements over RDS
    • preventing reporting and analytic processing from interfering with the performance of the OLTP workload
  • EMR is ideal for
    • processing and transforming unstructured or semi-structured data to bring in to Amazon Redshift and
    • for data sets that are relatively transitory, not stored for long-term use.

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AWS Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.
  1. With which AWS services CloudHSM can be used (select 2)
    1. S3
    2. DynamoDB
    3. RDS
    4. ElastiCache
    5. Amazon Redshift
  2. You have recently joined a startup company building sensors to measure street noise and air quality in urban areas. The company has been running a pilot deployment of around 100 sensors for 3 months. Each sensor uploads 1KB of sensor data every minute to a backend hosted on AWS. During the pilot, you measured a peak of 10 IOPS on the database, and you stored an average of 3GB of sensor data per month in the database. The current deployment consists of a load-balanced auto scaled Ingestion layer using EC2 instances and a PostgreSQL RDS database with 500GB standard storage. The pilot is considered a success and your CEO has managed to get the attention or some potential investors. The business plan requires a deployment of at least 100K sensors, which needs to be supported by the backend. You also need to store sensor data for at least two years to be able to compare year over year Improvements. To secure funding, you have to make sure that the platform meets these requirements and leaves room for further scaling. Which setup will meet the requirements?
    1. Add an SQS queue to the ingestion layer to buffer writes to the RDS instance (RDS instance will not support data for 2 years)
    2. Ingest data into a DynamoDB table and move old data to a Redshift cluster (Handle 10K IOPS ingestion and store data into Redshift for analysis)
    3. Replace the RDS instance with a 6 node Redshift cluster with 96TB of storage (Does not handle the ingestion issue)
    4. Keep the current architecture but upgrade RDS storage to 3TB and 10K provisioned IOPS (RDS instance will not support data for 2 years)
  3. Which two AWS services provide out-of-the-box user configurable automatic backup-as-a-service and backup rotation options? Choose 2 answers
    1. Amazon S3
    2. Amazon RDS
    3. Amazon EBS
    4. Amazon Redshift
  4. Your department creates regular analytics reports from your company’s log files. All log data is collected in Amazon S3 and processed by daily Amazon Elastic Map Reduce (EMR) jobs that generate daily PDF reports and aggregated tables in CSV format for an Amazon Redshift data warehouse. Your CFO requests that you optimize the cost structure for this system. Which of the following alternatives will lower costs without compromising average performance of the system or data integrity for the raw data?
    1. Use reduced redundancy storage (RRS) for PDF and CSV data in Amazon S3. Add Spot instances to Amazon EMR jobs. Use Reserved Instances for Amazon Redshift. (Spot instances impacts performance)
    2. Use reduced redundancy storage (RRS) for all data in S3. Use a combination of Spot instances and Reserved Instances for Amazon EMR jobs. Use Reserved instances for Amazon Redshift (Combination of the Spot and reserved with guarantee performance and help reduce cost. Also, RRS would reduce cost and guarantee data integrity, which is different from data durability)
    3. Use reduced redundancy storage (RRS) for all data in Amazon S3. Add Spot Instances to Amazon EMR jobs. Use Reserved Instances for Amazon Redshift (Spot instances impacts performance)
    4. Use reduced redundancy storage (RRS) for PDF and CSV data in S3. Add Spot Instances to EMR jobs. Use Spot Instances for Amazon Redshift. (Spot instances impacts performance and Spot instance not available for Redshift)

References