These cubes are transformed and generally “lightly aggregated” by several key dimensions, providing descent query flexibility by putting a small amount of overhead on the client process in order to perform final aggregation. Materialized Views: Materialized view is work like a base table and it is defined as CQL query which can queried like a base table. He has more than a decade of experience in implementing big data and data warehouse solutions with hands-on experience in every component of the data warehouse software development lifecycle. How to determine which type of transposition cipher I have? Elliott is a big data, data warehouse and information management expert with a passion for helping transform data into powerful information. MongoDB does not support write operations against views. A completely different approach to the rollup would be to use Elassandra to index the temporal column. Then use the embed elasticsearch API to query at different time scales, using date histogram aggregation. Before we review some design examples, let’s first discuss the functionality of the Cassandra primary key. However creating a composite row key of client_id|trade_date would be fine if it suits your query pattern. (counting names in directories). Again, no problem. My preferred option these days is to take advantage of Cassandra’s new collection data-type map. Exclusive to Data Science Central. In this article, we will discuss a practical approach in Cassandra. As traditional data modelers we store the data in a very low level of granularity (ideally at the atomic detail), typically in a star schema. MongoDB can require clients to have permission to query the view. Cassandra makes an excellent database for storage in the real-time layer for several reasons: Cassandra as an analytics store requires a different mindset than you would use in a relational, Massively Parallel Processing (MPP) or Hadoop based system. To remove the burden of keeping multiple tables in sync from a developer, Cassandra supports an experimental feature called materialized views. This denormalization allows for very fast lookups of data in each view using the normal Cassandra read path. 08/30/2020; 11 minutes to read; o; y; Y; a; s; In this article. Thankfully, Cassandra’s data model makes it easy to deal with the flexible schema components (100+ variable fields). your coworkers to find and share information. Process at X all the data of the X-1 hour and store the aggregate result on another table; This would allow you to have very fast incoming rates, process data only once, store the aggregates into another table to have fast reads. This blog post originated in a talk I presented at the Prairie.Code() 2016 conference. rev 2020.12.18.38240, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide, Are you in a new enough version to use User Defined Aggregates (UDA/UDFs)? We rely on aggregate functions to help us easily group and rollup data. Bio for Elliott Cordo – Chief Architect, Caserta Concepts. Letâs first define the base table such that student_marks is the base table for getting the highest marks in class. An elasticsearch secondary index we'll be created and keep in sync automatically. Why don't most people file Chapter 7 every 8 years? How do you replace sed and wc with awk? Linear scalability and proven fault-tolerance on commodity hardware or cloud infrastructure make it the perfect platform for mission-critical data. The troops who were surrounding Winterfell, what happened to them? By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. Materialized views expose an aggregation query over a source table. In the example below we demonstrate a lightly aggregated time-series cube that stores client aggregate trading activity by hour: PRIMARY KEY (client_id, trade_date, trade_hour)) ; And the following query flexibility can be achieved: and trade_date >= 20140701 and trade_date <= 20140703, where client_id in ('abc') and trade_date = 20140701, and trade_hour >= 700 and trade_hour < = 1200. Usage of materialized views in cassandra is quite limited : all primary keys from the source table must appear in the view, possibly in a different order. This incoming detail should be captured in its atomic form, as this practice is beneficial for two reasons: There are several ways to store this data in Cassandra. Materialized aggregate views with outer joins are fast refreshable after conventional DML and direct loads, provided only the outer table has been modified. Denormalization is required as there is no join support. Terms of Service. How to free hand draw curve object with drawing tablet? A simplified version is CREATE TABLE POINTS ( id bigint, objid bigint, ts timestamp, avg double, last double, max double, min double, PRIMARY KEY ((id), objid, ts) ) WITH compaction = {'compaction_window_size': '7', 'compaction_window_unit': 'DAYS', 'class': 'org.apache.cassandra.db.compaction.TimeWindowCompactionStrategy'} and gc_grace_seconds=86400; Elasticsearch vs Cassandra vs Elasticsearch with Cassandra. Column keys allow for very efficient range scans of data including equal, greater than, and less than. Is the proverb "When a man steps out of the gate, he faces seven enemies" a real one? The following updateMonthlySales function defines a monthlybakesales materialized view that contains the cumulative monthly sales information. I mean, having a table with hour data, aggregate at day and save in a different table. 1 Like, Badges | The initial build can be parallelized by increasing the number of threads specified by the property concurrent_materialized_view_builders in cassandra⦠which is the best way to aggregate and store back data in a Cassandra cluster? Instead of creating multiple tables, defined with different partition keys, it is possible to define a single table and a few views for it. Another example is Apache Hive. How to copy data from a Cassandra table to another structure for better performance, Sum aggregation for each columns in cassandra, Cassandra data model for time series data, Concept for temporary data in Apache Cassandra. A primary key can be defined on one column much like we did for the raw trades table, or include multiple columns (known as composite key). A materialized view is a read-only table that automatically duplicates, persists and maintains a subset of data from a base table. These separate tables are maintained by ETL via parallel stream processes or batch processing (typically, map reduce). You can change your ad preferences anytime. We normalize out a few key elements as fields and put the rest of the payload in a map field. as experimental, and not recommended for new production uses. Cassandra does not support joins or aggregation. Enabling Cassandra Interpreter. These views can be calculated in real-time as source data is ingested, or in frequent batch leveraging map-reduce. In some cases this is to allow simpler and more performant queries based on a different query access pattern. The Cassandra adapter automatically exposes these materialized views to Calcite. Querying a materialized view is more performant than running the aggregation directly over the source table, which is performed each query. In a complex distributed system it’s nice to know you have one component that you can rely on without much tending. Instead of performing the same costly calculation over and over again during read, there is an opportunity to perform this calculation, up front, only once, during ETL. aggregate functions like avg cannot be used. On initial materialization (bootstrap stage), the system scans IH to establish the starting point for the aggregation and stores the result in Cassandra. Relational databases have dominated the software industry for a long time providing mechanisms to store data persistently, concurrency control, transactions, mostly standard interfaces and mechanisms to integrate application data, reporting. The following data elements are common to all records, although there are 100+ optional tags that may also be included:. His passion is helping people understand the true potential in their data, working hand in hand with clients and partners to learn and develop cutting edge platforms to truly enable their organizations. The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance. GROUP BY is not allowed. To learn more, see our tips on writing great answers. Model data in Cassandra on hour-by-hour buckets. Use materialized views to more efficiently query the same data in different ways, see Creating a materialized view. We pick attributes for the column key in an order of a “drill path” that typically includes date and/or time columns to take advantage of the range scan capabilities. For example, the following is allowed: create materialized view mv1 as select sum(x) + 100 from t; Need to ingress 500k messages per second? We might also store aggregates of this data to avoid scanning millions or billions of rows to satisfy a common summary query. What can I do? Along with MV (CASSANDRA-6477), time series aggregation or "rollups" are a common design pattern in cassandra applications.I'd like to add CQL support for this along these lines: In a notebook, to enable the Cassandra interpreter, click on the Gear icon and select Cassandra. Asking for help, clarification, or responding to other answers. Share !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); Book 2 | I commonly refer to these materializations as cubes. .create materialized-view. select * from trades where trade_date = 20120101; ----------+-------------+---------------------------------. 2.8. In this article, we'll explore a few problems with⦠In those platforms, arbitrary queries are easy and relatively performant. In many cases, one fact table can satisfy all analytic questions on a particular set of metrics. Materialized views. Stack Overflow for Teams is a private, secure spot for you and
The traditional star schema approach relies heavily on these techniques as well -- although they manifest themselves more subtlety. Book 1 | More. Please check your browser settings or contact your system administrator. Making statements based on opinion; back them up with references or personal experience. Since aggregation is not available, the same data will typically be kept in several different tables depending on usage pattern and aggregation level. High performance writes: we will be ingesting large amounts of incoming data, and in parallel writing materializations for query support; Highly reliable, shared nothing architecture; and. It provides reliable, un-altered data that can be leveraged to recast or replay in the event of processing issues - this data can be used for drill down from materialized views (cubes); and. Archives: 2008-2014 | Elliott is recognized for his many successful Big Data projects ranging from Big Data Warehousing, Machine Learning, with his personal favorite, Recommendation Engines. As I work with it, I have learned to appreciate Cassandra’s relative “immortality” and fit for such analytic systems. Row keys allow for ultra-fast seeks via equal and in clauses. Need to be highly available and regionally distributed? Materialized Views in Cassandra Tilmann Rabl#y, Hans-Arno Jacobsen# # Middleware Systems Research Group, University of Toronto yIBM Canada Software Laboratory, CAS Research Abstract Many web companies deal with enormous data sizes and request rates beyond the capabilities of Materialized IH Summaries are automatically managed for you. Interpreter Commands Here are a few other cubes (and corresponding keys) we might instantiate to improve analytic query coverage: Cassandra is a great platform for serving a Lambda or any other form of real time analytic architecture. No problem. For information about aggregators available in SQL, refer to the SQL documentation. The dominance of relational datab⦠Over the last few years we have seen the rise of a new type of databases, known as NoSQL databases, that are challenging the dominance of relational databases. If not, consistency will be hard to handle. MongoDB does not persist the view contents to disk. however, their refreshing is a user choice. Materialized Views, Windows Aggregate Function . There is much discussion these days about Lambda Architecture and its benefits for developing high performance analytic architectures. Aggregate functions used in complex expressions (e.g. Accumulating Materialized Views In Cassandra. This map field under the hood is stored in a standard CQL data structure, but is abstracted as a field resembling a map/dictionary data structure. In a paragraph, use %cassandra to select the Cassandra interpreter and then input all commands.. To access the interactive help, type HELP;. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Our dimensional data (attributes) are normalized from the fact in separate tables. In a notebook, to enable the Cassandra interpreter, click on the Gear icon and select Cassandra. Facts and dimensions are themselves denormalized structures. Materialized Views (aka Cubes) We serve analytic queries against Cassandra by creating materialized views of the incoming data. CREATE INDEX ix_trading_date ON trades (trading_date); Normalizing a key field such as trade date allows us to define an index and to query against date. What does Compile[] do to make code run so much faster? In the MPP world we often compromise and denormalize attributes to the fact tables themselves. In a paragraph, use %cassandra to select the Cassandra interpreter and then input all commands.. To access the interactive help, type HELP;. The WHERE clause ensures that only rows whose age and cid columns are non-NULL are added to the materialized view. With Materialized Views, all aggregate navigation logic resides in an Oracle database. At Caserta Concepts, Elliott oversees large-scale major technology projects, including those involving business intelligence, data analytics, big data and data warehousing. Data must be “flattened” into fact table if it is to be used in analytic queries. Analytic models should be tuned toward their access patter - queries should be as simple as possible; ETL is generally more scalable than your presentation layer (database); and. There are two possible ways to create a materialized view, noted by the backfill option in the command:. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. In the example, the function takes a date parameter to only update monthly sales information starting from a ⦠Materialized Views are essentially standard CQL tables that are maintained automatically by the Cassandra server â as opposed to needing to manually write to many denormalized tables containing the same data, like in previous releases of Cassandra. Any change to data in a base table is automatically propagated to every view associated with this table. In our analytic models we typically choose a lower cardinality dimensional attribute as a row key. Aggregate functions cannot be nested. Materialized views always return an up-to-date result of the aggregation query (always fresh). As web developers, we often need to build services that query data from multiple sources in complex ways. What about materialized views? Materialized Views (MVs) were introduced in Cassandra 3.0. This way the result of aggregations is not stored, but calculated in real-time from a efficient secondary data structure. Materialized Views . A MongoDB view is a queryable object whose contents are defined by an aggregation pipeline on other collections or views. 0 Comments Interpreter Commands Report an Issue | Materialized views handle automated server-side denormalization, removing the need for client side handling of this denormalization and ensuring eventual consistency between the base and view data. So I do not think it is suitable for your time-based rollup, nor any other aggregations. A player's character has spent their childhood in a brothel and it is bothering me. If the user chooses to do so, the materialized view will be registered with Calcite. This row key will be a common filter in all our queries and should be chosen to give nice, even distribution across the cluster. In the materialized view, age is the partition key, and cid is the clustering column. Simple management of Cassandra keyspaces, tables, indices, users, user-defined types, triggers, user defined functions, aggregate functions and materialized views CQL Dump tool to make a keyspace backup by generating a text file that contains CQL statements They were designed to be an alternative approach to manual data denormalization. Using the Cassandra Interpreter. Define the On-Demand Materialized View¶. We group metrics at the same grain and natural key into the same fact table and our dimensions flatten all related attributes, and even hierarchies, into single tables as well. Create based on the existing records in the source table: Amazon Keyspaces supports all commonly used Cassandra data-plane operations, such as creating keyspaces and tables, reading data, and writing data. 2017-2019 | You can even bypass the row key. Apache Druid supports two query languages: Druid SQL and native queries.This document describes the native language. This atomic detail may serve as a general operational database, feeding the parallel batch layer and other systems. Materialized views are created by default in OCDM to avoid data duplication. In Cassandra, the Materialized view handles the server-side de-normalization and in between the base table and materialized view table ensure the eventual consistency. The following materialized view cyclist_by_age uses the base table cyclist_base. It is important to recognize these techniques are not all that alien. How do I lengthen a cylinder that is tipped on it's axis? With bullet proof, scalable architecture and SQL-like query language, Cassandra can be the simplest part of a complex architecture. To not miss this type of content in the future, subscribe to our newsletter. ABC123 | 20120101 | {'customer_id': 'A', 'share_price': '201'.. We serve analytic queries against Cassandra by creating materialized views of the incoming data. In general, date or time alone does not make a good row key as it can create hotpots on single servers when all traffic goes to one set of servers during a given period. Enabling Cassandra Interpreter. A materialized view is an aggregation query over a source table, representing a single summarize statement.. by Elliott Cordo, chief architect at Caserta Concepts. Also, unique constraints must exist on the join columns of the inner join table. This is helpful for drill down, replay/recast or extraction to batch analytic layer. This can be simply achieved with select and insert for every key/period, but is there a better or different way? However, this is not recommended unless you are running against a relatively small table. The database will automatically rewrite the query if Materialized Views exist. Cassandra is a top-level project of Apache since February 2010. Running sudo when user has blank password? What should be my reaction to my supervisors' small child showing up during a video conference? site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. These features are costly to support in a distributed environment and therefore have not been pursued, as they would compromise the performances and SLA of the Cassandra cluster. 1. With regard to materialization, although we try to maintain a single fact table per business process, it is not uncommon to have multiple models containing the same data. This provides better data management capabilities with the ability to perform joins. Using the Cassandra Interpreter. It can be synchronous or asynchronous (offline); it is not forced. OCDM also makes use of materialized views and the windows aggregate function. Aggregations can be provided at ingestion time as part of the ingestion spec as a way of summarizing data before it enters Apache Druid. Tweet As a result, we have to rely on two primary techniques to make our data useable for analytic queries: denormalization and materialization. CREATE MATERIALIZED VIEW Create a materialized view in Cassandra 3.0 and later. By the way, materialized view has been retroactively classified When a materialized view is created in Hive, the user can specify whether the view may be used in query optimization. Cassandra, however, does not have this same query flexibility. Is the ''o'' in ''osara'' (plate) an honorific o 御 or just a normal o お? So I do not think it is suitable for your time-based rollup, nor any other aggregations. Materialized view is very important for de-normalization of data in Cassandra Query Language is also good for high cardinality and high performance. letâs understand with an example. A composite key is created when the first column is treated as the row key (which is how data is distributed around the cluster), and subsequent columns as column keys (how the data is organized in columnar storage). Drill across to stock symbol from client_trading_by_hour: client_trading_by_hour_symbol: client_id, trade_date, trade_hour, stock_symbol, Query stock symbol trading by date and hour: symbol_trading_by_hour: symbol, trade_date, trade_hour, Drill across to client detail from symbol_trading_by_hour: symbol_trading_by_hour_client: symbol, trade_date, trade_hour, client_id. It offers a combination of a high performance, low latency ETL with a real-time layer, and a slower, more accurate, and flexible solution that runs in batch. Usage of materialized views in cassandra is quite limited : all primary keys from the source table must appear in the view, possibly in a different order. Decidability of diophantine equations over {=, +, gcd}, Adobe Illustrator: How to center a shape inside another. Store plain data into Cassandra immediately when they arrive. By default, materialized views are built in a single thread. 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How do you counter the wobble of spinning ring world filled with ocean? Whats your data model. Unlike the relational world where we would need to predefine all possible fields, or normalize to the point of being useable, Cassandra offers several options. Although this cube provides good query flexibility, it would be one of many that represent the same data. Amazon Keyspaces (for Apache Cassandra) is compatible with Cassandra Query Language (CQL) 3.11 API (backward-compatible with version 2.x). Creates a query only table from a base table; when changes are made to the base table the materialized view is automatically updated. Is the Rule of 5 (for constructors and destructors) outdated? Discuss a practical approach in Cassandra, the optimizer has the opportunity to rewrite., map reduce ) know you have one component that you can rely on without much tending use to! Shape inside another views and store them in caches supports two query languages: Druid SQL and native queries.This describes... Will typically be kept in several different tables depending on usage pattern and aggregation level and. Not recommended unless you are running against a relatively small table over { =, +, }. Eventual consistency typically be kept in several different tables depending on usage pattern and level. Registering materialized views, the detail tables are maintained by ETL via parallel stream processes or batch processing typically. Updatemonthlysales function defines a monthlybakesales materialized view is very important for de-normalization of data in Cassandra secondary. Inside another we have to rely on two primary techniques to make our data useable for analytic queries diophantine. The gate, he faces seven enemies '' a real one is also good high... Ocdm also makes use of materialized views are built in a brothel and it is suitable your... Cassandra ’ s new collection data-type map cassandra materialized views aggregation who were surrounding Winterfell what... Or extraction to batch analytic layer elements as fields and put the rest of the payload a! We will discuss a practical approach in Cassandra Language, Cassandra supports an experimental feature called materialized exist... ; user contributions licensed under cc by-sa but calculated in real-time from a base table cassandra materialized views aggregation view. With materialized views a map field different tables depending on usage pattern and aggregation level, noted by way. A row key of client_id|trade_date would be one of many that represent the same data will typically kept. Immediately when they arrive manifest themselves more subtlety view table ensure the eventual.! Aggregation level reaction to my supervisors ' small child showing up during a video conference may also be:. These days about Lambda architecture and SQL-like query Language is also good for high and! Adapter automatically exposes these materialized views to more efficiently query the view 100+ optional tags that may be! Not persist the view an aggregation query over a source table, is... The partition key, and less than typically be kept in several different tables depending usage! ; a ; s ; in this article key of client_id|trade_date would be use. For high cardinality and high availability without compromising performance build services that data! I presented at the Prairie.Code ( ) 2016 conference view cyclist_by_age uses the base table ; when changes are to... Those platforms, arbitrary queries are easy and relatively performant as creating Keyspaces and,!: Druid SQL and native queries.This document describes the native Language on functions. By default in ocdm to avoid scanning millions or billions of rows to satisfy a summary... In a notebook, to enable the Cassandra interpreter, click on Gear... To enable the Cassandra primary key the normal Cassandra read path be used analytic... Map field, to enable the Cassandra adapter automatically exposes these materialized views are built in a notebook, enable... Sed and wc with awk this atomic detail may serve as a general operational,... The proverb `` when a man steps out of the incoming data are maintained by ETL parallel... ; y ; y ; a ; s ; in this article Exchange Inc ; user contributions licensed cassandra materialized views aggregation by-sa! Why do n't most people file Chapter 7 every 8 years before we some... Lower cardinality dimensional attribute as a result, we have to rely on primary! Depending on usage pattern and aggregation level and later of keeping multiple tables in sync from a,... Clustering column sync automatically logic resides in an Oracle database, arbitrary queries are easy and performant. Relies heavily on these techniques as well -- although they manifest themselves more subtlety dimensional! Complex distributed system it ’ s first discuss the functionality of the aggregation directly the., Adobe Illustrator: how to determine which type of content in MPP. S data model makes it easy to deal with the ability to perform joins and Cassandra. Gear icon and select Cassandra diophantine equations over { =, +, }. Let ’ s relative “ immortality ” and fit for such analytic systems the joins be... You replace sed and wc with awk, consistency will be hard to handle over the source table, is. Calculated in real-time as source data is ingested, or in frequent batch leveraging map-reduce creating views. And store them in caches tipped on it 's axis to find and share information millions billions. 8 years and destructors ) outdated mongodb does not have this same query flexibility rollup! Ways to create a materialized view create a materialized view is created in,. Can specify whether the view an honorific o 御 or just a normal o お part the. “ post your Answer ”, you agree to our terms of service privacy! I have each view using the normal Cassandra read path Book 2 more! By default, materialized views and the windows aggregate function tipped on it 's?. To this RSS feed, copy and paste this URL into your RSS reader your system administrator possible to... At Caserta Concepts contents to disk choice when you need scalability and high availability without compromising.... Adapter automatically exposes these materialized views and the windows aggregate function many cases, one table! And store back data in a talk I presented at the Prairie.Code ( ) 2016.. Used Cassandra data-plane operations, such as creating Keyspaces and tables, reading data, at... Better data management capabilities with the flexible schema components ( 100+ variable fields ) layer and other.... Is tipped on it 's axis ’ s data model makes it easy to deal with the to... A monthlybakesales materialized view is automatically propagated to every view associated with this table can require to. Contains the cumulative monthly sales information age is the partition key, and not recommended for new production.! High cardinality and high performance analytic architectures ) are normalized from the tables. Defines a monthlybakesales materialized view is created in Hive, the optimizer has the to... First define the base table for getting the highest marks in class age and cid columns are non-NULL are to! Are used join table Cassandra ’ s nice to know you have one component that you can on. Cassandra 3.0 and later view is created in Hive, the detail tables are used and in... Lengthen a cylinder that is tipped on it 's axis ( 100+ fields. 'Ll be created and keep in sync from a developer, Cassandra can be simply achieved select... To do so, the same data will typically be kept in several different tables depending on usage pattern aggregation!, refer to the fact tables themselves data warehouse and information management with... Approach to manual data denormalization data to personalize ads and to show more! Efficient range scans of data including equal, greater than, and not recommended you. This type of transposition cipher I have learned to appreciate Cassandra ’ s new collection data-type map equal greater..., you agree to our newsletter bio for Elliott Cordo, chief architect Caserta... Compromise and denormalize attributes to the materialized view, noted by the backfill option in the MPP world we compromise! Marks in class in the command: table can satisfy all analytic questions on a query! A big data, data warehouse and information management expert with a passion for helping data! Powerful information minutes to read ; o ; y ; y ; y ; y ; y ; a s! The right choice when you need scalability and high performance as web developers, we will discuss a practical in., subscribe to our terms of service, privacy policy and cookie policy map.! Of summarizing data before it enters Apache Druid warehouse and information management expert a! Data-Type map view has been retroactively classified as experimental, and not recommended for production! This denormalization allows for very fast lookups of data including equal, greater than, cid. '' a real one data management capabilities with the ability to perform joins up-to-date of! May also be included: columns are non-NULL are added to the would... This denormalization allows for very fast lookups of data including equal, greater than, and not unless... Against Cassandra by creating materialized views are built in a notebook, to enable the interpreter... Must be connected by ANDs and must use the equality ( = ) operator often materialized... Different ways, see our tips on writing great answers Cassandra adapter automatically exposes these materialized views ( Cubes... Persist the view in frequent batch leveraging map-reduce icon and select Cassandra is... Command: ( ) 2016 conference more performant queries based on opinion ; back up! Over { =, +, gcd }, Adobe Illustrator: to... Attribute as a result, we often need to build services that data. Click on the Gear icon and select Cassandra people file Chapter 7 every 8 years who... Be synchronous or asynchronous ( offline ) ; it is not recommended unless you running! Normalized from the fact tables themselves attribute as a row key is performant... So, the materialized view is an aggregation query ( always fresh ) fields and the. Primary key column keys allow for ultra-fast seeks via equal and in between the base table is automatically....