DynamoDB is a fully managed, highly-available database with replication across multiple AZs
NoSQL – not a relational database! – just simple key:value
single digit millisecond performance.
scales to massive workloads
100TBs of storage
fast and consistence, low latency retrieval
integrated with iam for security authorization and admin
enables event-driven programming via DynamoDB Streams
low cost and auto-scaling
important for exam:
no db provisioning needed you just create a table
Has two able classes: standard and infrequent access IA table class
Basics of DynamoDB
v important – also exam q:
made up of tables – there is NO SUCH THING AS A DATABASE – you only need to create tables!
the db already exists!
you just create tables –
each table has a primary key – must be set at creation time
each table can have an infinite number of items ie rows
each item has attributes can be added over time or they can be null
this is much easier to do at any time than with a conventional relational db.
max size of an item is 400KB so not good for large objects
data types supported are:
scalar types: string, number, binary, boolean, null
document types: list, map
set types: string set, number set, binary set
have primary key – containing partition key (eg user_id) and sort key (eg game_id)
attributes: eg score, result – these are items which are NOT the primary key
Is a great choice for a schema where you need to rapidly evolve the schema, better than the others for this.
read/write capacity modes
control how you manage your table capacity – ie the read and write throughput
2 Capacity Modes for DynamoDB
important for exam:
Provisioned mode – is default, provisioned in advance
we have 2 possible capacity modes:
provisioned mode, where you specify number of read and writes per second, this is the default.
very good for predictable modes.
You have to plan the capacity for this in advance, you pay for provisioned read capacity units RCUs and write capacity units (WCUs)
these “capacity units” are used to set your desired capacity for your database! – set these in the web dashboard of dynamodb when you are provisioning.
you can also add auto scaling mode for both rcu and wcu
on-demand mode – much more expensive, but better for unpredictable workloads or sudden transaction spikes where provisioned mode cant scale sufficiently
read write automatically scales up and down acc to workload, so no capacity planning needed
you pay for your use, is more expensive 2-3x more
good for unpredictable workloads which can be large or small varying
need to know for exam!
remember always you just create tables, never a database with dynamodb!
you can specify read and write capacity autoscaling separately
DynamoDB Accelerator DAX
a fully manageable, highly available seamless in-memory cache for dynamodb
helps solve read congestion by means of memory caching
microseconds latency for cached data
does not require any application logic modification – so it is fully compatible with existing dynamodb api
applications can access the database via DAX for much faster reads
TTL is 5 mins default for dax data
dax is different from elasticache in that it is meant for dynamodb and does not change the api
good for individual object cache
good for storing aggregation result where further processing required
very easy – is an ordered stream of data that represents items when created or updated or deleted
can then be sent on to kinesis datastreams
can be read by lambda or kinesis client library apps
data is retained for 24 hrs
reacting to changes in real time eg welcome emails to new users
to do analytics
to insert into derivative tables or into elastic serarch
or implement cross region replication
Summary of DynamoDB Streams
So, to summarize DynamoDB Streams
Application -> create/update/delete actions to the TABLE -> Dynamo DB Streams
and from the TABLE -> Kinesis Data Streams -> Kinesis Data Firehose
Kinesis Data Firehose
-> for analytics -> Redshift
-> for archiving -> S3
-> for indexing -> OpenSearch
DynamoDB Global Tables
two way or multi-way replication
to provide for low latency across regions
this means apps can read and write to the table from any region
must enable dynamodb streams for this
TTL expiry: automatically deletes items after an expiry timestamp
eg 1 month for each row in the table
DynamoDB Indexes – only need to know at high level for exam
basically, these allow you to query on attributes other than the primary key
gsi – global secondary and lsi – local secondary
(all you need to know for now)
by default you query on the primary key, but you can use gsi or lsi to query on other attributes.
Transactions in DynamoDB
these allow you to write to 2 tables at the same time:
the transaction however MUST write to both or else none – in order to keep the tables accurate – so data consistency is maintained