This short presentation examines some common challenges that can occur when querying a distributed RDBMS. Challenges & Solutions

1. Challenges in Querying a
Distributed Relational Database

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The Challenges of Querying a Distributed RDBMS
This presentation examines some common
challenges that can occur when querying a
distributed RDBMS.
- Challenges
- Solution

3. Challenges

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The Challenges of Querying a Distributed RDBMS
A distributed relational database can give your
application unlimited scalability.
However, a number challenges can occur when
querying a distributed RDBMS.
1. Aggregation
2. Distinctive Value
3. Joins
4. Sub-Queries
5. The “Combination”

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1 - The Aggregation Challenge
• Let’s assume that a company stores the HR data
of several departments across multiple partitions.
• When requesting the average salary of all
employees, all departments must be examined.
• If the average salary is calculated separately on
each partition and later amalgamated with all
other results, the final result will be inaccurate.

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2 - The Distinctive Values Challenge
• Data entries, such as age or salary, will often repeat
throughout the database.
• Finding identical values across multiple partitions can
skew data analysis and produce false query results.
• When an application requests a list of distinct values,
the data needs to be processed in a way where
repetitions are eliminated from result set.

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3 - The Joins Challenge
• Ideally, records that exist in different partitions
should be joined after considering all of the query
criteria.
The Sharding Conflict - attempting multiple joins from
records that are situated across various partitions
poses a challenge due to the Sharding Conflict

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4 - The Sub-Queries Challenge
• Often the result of one query is needed to complete
another query. This brings dependencies and
complexity into the system.
For instance, a query examining all employees with
above average salaries requires a sub-query to
determine the average salary, considering all partitions.
In order to yield correct results, this sub-query has to
be processed independently, and before the parent
query.

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5 - The “Combination” Challenge
• Any combination of:
• Aggregation
• Distinctive Values
• Joins
• Sub-Query
For example, trying to get an average of the distinctive
values of salary.
In order to accomplish this, we first need to eliminate
repetitions and only then aggregate. It’s impossible to do
both together.

10. Solution

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Meeting the Challenges
• DBAs need to carefully consider how to arrange data
across multiple partitions in a distributed database.
• Distributing the data with
intelligence about the application,
schema and workloads will help
you avoid many conflicts.
• place data together what is used together
• Cross-partition queries will always exist. Considering the
nature of the queries and the application is key to
creating a functional distributed database.

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