Amazon Cloud Concepts Learning --> Day20

Amazon DynamoDB

Fully managed schema-less NOSQL database service.
Non-Relational, Key/value and document store.
It has Four 9s. (99.99%) of availability (5 in case of global tables)
Data is synchronously replicated across 3 different availability zones within a single region.
Data is stored in SSD Storage.
Offers encryption at rest.
Multi-AZ Redundancy and Cross-Region Replication option is available.
Session state data may be stored using DynamoDB.
As a serverless service, DynamoDB requires no provisioning or managing of instances.
DynamoDB is made up of

Tables --> Tables are collection of items.
Items --> basically a row (Maximum record size is 400KB) Partition key and Sort Key make up the Primary Key used access items in the tables (primary key is also known as Composite Key when both attributes are present - you can also specify a PK without SK).
Attributes --> the information associated with that item (columns).

Since DynamoDB is schema less, once you defined the structure of the primary key (Partition and Sort Keys), every item/row can have its own structure.
TTL (TimeToLive) defines when items in a table expire and they will be automatically deleted.

DynamoDB Backups and Restore

On demand backups are non-expiring and may be planned. They are completed in a matter of seconds, with no effect on table availability or performance.
On demand backups are non-expiring and may be planned. They are completed in a matter of seconds, with no effect on table availability or performance.

DynamoDB Streams

Whenever a record is added, changed, or withdrawn from a DynamoDB database, it is written to the stream and kept there for a maximum of 24 hours.
Streams enable the recording of an item-level change sequence that is time-ordered.
You can construct a trigger—code that executes automatically whenever an event of interest occurs in a stream—by combining DynamoDB Streams with AWS Lambda.
In addition, the event timestamp, the table name, and other metadata are included in each stream record.

Secondary Indexes

Permits you to do searches against the primary key in addition to queries against the data in the table using an alternate key.
A table may have one or more secondary indexes created for it.
Two kinds of Indexes

Global Secondary Index --> An index with a partition key and sort key that can be different from those on the table.

Local Secondary Index --> An index that has the same partition key as the table, but a different sort key.
There is a default quota of 20 global secondary indexes and 5 local secondary indexes for each DynamoDB table.

DynamoDB Consistency

The user can choose between the two consistency models offered by DynamoDB when reading data: eventually consistent and strongly consistent.

Eventually Consistent Reads

The read throughput is maximized by the eventual consistency option.
Usually, consistency is achieved across all copies in a few of seconds.
Nevertheless, the outcomes of a recently finished writing might not be reflected in an eventually consistent read.
After a little while, repeating a read ought to yield the updated data.
By default, DynamoDB employs eventually consistent reads.

Strongly Consistent Reads

A very consistent read yields a result that includes all writes that were answered successfully before the read.
Strongly consistent reads are only supported on tables and local secondary indexes.
Strongly consistent reads use more throughput capacity than eventually consistent reads.
Read operations such as GetItem, Query, and Scan provide an optional ConsistentRead parameter.

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Amazon DynamoDB - Part1

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