Explore Cosmos DB Flashcards
1
Q
What is cosmos DB?
A
- Fully managed NOSQL DB designed to provide low latency, elastic scalability of throughput, well-defined semantics for data consistency and high availability
2
Q
What are the benefits of cosmos DB global distribution?
A
- can achieve low latency by placing in the region closest to users
- can add or remove regions associated with an account at any time
- the app doesn’t need to be paused or redeployed to add or remove region
- every region supports reads and writes with 99.999% availability
- Guaranteed reads and writes served in less than 10ms at the 99th %tile
- CosmosDB internally handles the data replication between regions with consistency-level guarantees
- if one region goes down the others will pick up the load
3
Q
What is a cosmos DB account?
A
- Fundamental unit of global distribution and high availability
- contains unique DNS name
- managed via portal, CLI or SDKS
- can add or remove regions to your account at any time
- can create 50 accounts under a subscription
4
Q
What is a cosmosDB container?
A
- fundamental unit of scalability
- you can virtually have unlimited provisioned throughput (RU/s) and storage on a container
- ComosDB transparently partitions container using the logical partition key that you specify to scale your provsioned throughput and storage elastically
- container is a schema agnostic container of items
5
Q
What is the cosmos DB hierarchy?
A
- Accounts -> databases -> containers -> items (stored procs, functions, triggers etc)
6
Q
What is the defintion of a cosmosDB?
A
- unit of management for a set of azure cosmos DB containers
7
Q
How is a container partitioned?
A
- Horizontally partitioned and then replicated across multiple regions
- items you add to it are auto grouped into logical partitions which are distributed across physical partitions based on a partition key
- throughput is evenly distributed across physical partitions
8
Q
How is throughput on a container configured?
A
- Dedicated provisioned throughput mode; the throughput provisioned on a container is exclusively reserved for the container and its backed by the SLAs
- shared provisioned throughput mode; containers share the throughput with other containers in the same DB
9
Q
What is a cosmosDB item?
A
- depending on which API you use an item can be a doc in a collection, a row in a table or a node or edge in a graph
- can have arbitrary schemas
- by default all items that you add to a container are automatically indexed without requiring explicit index or schema management
10
Q
How does cosmosDB approach data consistancy?
A
- As a spectrum of sources
- strong consistency and eventual consistency are at the ends of the spectrum
- the further away from strong you are the higher availability, lower latency and higher throughput you will have
- region agnostic
- CosmosDB guarantees that 100% of read requests meet the consistency guarantee for the consistency level chosen
11
Q
What are the levels of data consistency?
A
- strong
- bounded staleness
- session
- consistent prefix
- eventual
12
Q
How can consistency modals be used?
A
- each one can be used for specific real-world scenarios
- you can configure detail consistency level on your azure cosmos DB account at any time
- it applies to all cosmos DB databases and containers under that account
13
Q
What is the strong consistency level of data consistency?
A
- offers linearizability (serving requests concurrently) guarantee
- reads are guaranteed to return the most recent committed version of an item
- client never sees an uncommitted or partial write
14
Q
What is the bounded stalness level of data consistency?
A
- reads are guaranteed to honour the consistent-prefix guarantee
- might lag behind writes by at most X versions (updates) of an item by Y time interval, whichever is reached first
- X and Y are staleness
- for single region min value of x and y is 10 write operations or 5 seconds
- for multi region min values are 100k and 300s
15
Q
what is the session consistancy level of data consistency?
A
- within a single client session reads are guaranteed to honour the consistent-prefix, monotonic reads, monotonic writes, read-your-writes, and write-follows-reads guarantees
- assumes a single writer session or sharing the session token for multiple writers
16
Q
What is the consistent-prefix level of data consistency?
A
- updates made as single doc writes see eventual consistency
- updates made as a batch within a transaction are returned consistent to the transaction in which they were committed
- write operations within a transaction of multiple docs are visible together
- assume 2 write operations performed on DOC1 and DOC2 by transactions T1 and T2
- when the client reads they will see either DOC1 v1 and DOC2 v1 or DOC1 v2 and DOC2 v2 never DOC1 v2 and DOC2 v2
17
Q
What is the eventual level of data consistency?
A
- no ordering guarantees for reads
- replicas eventually converge
- weakest form as client may read the values that are older than the ones it read before
- ideal when app doesn’t require ordering guarantees
- e.g. retweets, likes or nonthreaded comments
18
Q
What APIs does cosmos DB offer?
A
- NoSQL
- MongoDB
- PostgreSQL
- Apache cassandra
- Table
- Apache Gremlin
19
Q
What are the benefits of cosmos DB offering multiple APIs?
A
- allows us to modal real-world data using docs, key/value, graph and column data models
- allows apps to treat cosmosDB as if it were various other DB technologies without the overhead of management and scaling approaches
20
Q
Which of the APIs ar native to cosmosDB
A
- API for NoSQL
- The rest implement the wire protocol of open source DB engines best suited for
– if you have existing apps using those technologies
– you don’t want to rewrite your entire data access layer
– you want to use open-source dev ecosystem
21
Q
What does the API for NoSQL provide?
A
- stores data in doc format
- best end-to-end experience as we have full control over interface, service and SDKs
- any new features rolled out for cosmosDB are available here first
22
Q
What does the API for mongoDB provide?
A
- stores data in doc BISON format
- doesn’t use any native mongoDB related code
- combines mongoDB ecosystem with cosmosDB features
23
Q
What does the API for postgreSQL provide?
A
- managed service for running postgreSQL at any scale
- stores data on single node or distributed in multi node config
24
Q
What does API for cassandra provide?
A
- column orientated
- highly orientated, horizontally scaling approach to storing large volumes of data while offering flexible approach to column orientated schema
25
Q
What does API for gremlin provide?
A
- allows users to make graph queries and stores data as edge and vertices
- useful for scenarios; involving dynamic data, data with complex relations, desire to use Gremlin
26
Q
- What does API for table provide?
A
- key/value format
- if you use azure table storage you may see some limitations in latency, scaling and throughput
- this API overcomes these issues
27
Q
What do we pay for in cosmosDB?
A
- throughput you provision and the storage you consume hourly
- throughput must be provisioned to ensure sufficient system resources are available for your DB at all times
28
Q
What is a Request Unit (RU)
A
- with cosmosDB operations is normalised and expressed as an RU
- represent the system resources such as CPU, IOPS and memory that are required to perform the DB operations supported by cosmos DB
29
Q
How much do operations cost in regards of RUs?
A
- the cost to do a point read (fetching a single item by ID and partition key value) for a 1KB item is 1RU
- all other operations are assigned a cost using RUs
- other CRUD operations (except READ) have variable number of RUs depending on the complexity of the operation
30
Q
What are the modes we can create a cosmos DB account in?
A
- provisioned throughput mode
- serverless mode
- autoscale mode
31
Q
What is the provisioned throughput mode for a cosmos DB account?
A
- you provision the number of Rus for you app on a per second basis in increments of 100 RUs per second
- you can increase or decrease RUs at any time to scale the provisioned throughput for app
- can make change programmatically or via portal
32
Q
What is the serverless mode for a cosmos DB account?
A
- you dont have to provision throughput when creating resources in cosmos account
- at end of billing period you get billed for number of RUs that have been used
33
Q
What is the autoscale mode for a cosmos DB account?
A
- you can auto and instantly scale the throughput RUs of your DB or container based on usage
- doesn’t affect availability, latency, throughput or performance of the workload
- well suited for mission-critical workloads that have variable or unpredictable traffic patterns and require SLAs on a high performance and scale
