a gentle introduction to event databases · 2016-05-16 · in the real world people carry out...
TRANSCRIPT
A gentle introduction to eventdatabases
Dino EspositoJetBrains
[email protected]@despos
facebook.com/naa4e
In the real world people carry out actions.
In software, we love to have models.
Actions alter the state and generate events.
In the real world, people observe events.
MODELING BASED ON BEHAVIOR
MODELING BASED ON DATA
ImmutableCan be
replayedActivity
log
EVENTS are the description of
something that happened.
YOU DON’T MISS A THING
for the entire lifetime of the system
Logging the list of
commands lets you
keep track of the
latest without
forgetting anything
that happened in
the past.
PS: if you really want to forget … go with plain CRUD.
DATA MODEL
USER EXPERIENCE USER EXPERIENCE
REQUIRED ACTIONS
DATA MODEL
REQUIRED ACTIONS
A DATA MODEL
AT THE FOUNDATION OF A
SOFTWARE SYSTEM
is cumbersome and coercing
BehaviorExpected UX
PersistencePolyglot data
POLYGLOT
DATA?To be best of my knowledge, I’m not biased
Sparse Thoughts
NoSQL came out to replace SQL but it only took rigor and diligence away from the data design process
• Which is, from the bottom of data upNoSQL didn’t change the way we envision systems
• None of works alone
• If one works alone is SQLTechnically speaking, NoSQL and SQL specializes in different areas
Polyglot means use the data model (aka, the tool) right for the job
Polyglot data pushes a task-oriented view of the system
Both SQL and NoSQL can be used, under
the hood, to save and read event data.
What’s event data, exactly?
Event Sourcing
All changes made to the application state during the entire lifetime of the system are stored as a sequence of events.
Events are your native data; hence, your data source.
Events are not common in the vast majority of today’s applications.
Today’s applications mostly store the current state and use it to process business transactions.
From CRUD to Historical CRUD
DEMO
Event-based
representation of data Event
Sourcing
CRUDCurrent State Storage
Event-based
representation of data
Projection
of dataProjection
of dataProjection
of data
Event-based
representation of data
Projection
of data
Projection
of data
Projection
of data
EVENT DATABASES
INTERNAL STORAGE
Aspects of an Event Database
Allows you to log application events
Requested, Created, Denied, Deleted, Postponed, …
Allows you to query application events
Last N events, all events since T1, all events from T2
More advanced features
Data streaming, subscriptions
CREATE Operations
CREATEDAGGREGATE
IDTIMESTAMP DETAILS
CREATEDAGGREGATE
IDTIMESTAMP DETAILS
CREATEDAGGREGATE
IDTIMESTAMP DETAILS
Request
Append new record
Global event ID
Some code describing the operation
Timestamp
Entity identifier
Information associated with the event
Information
Transparent storage: relational, NoSQL, graph
UPDATE Operations
CREATED 888998TIMESTAMP DETAILS
CREATED 123456TIMESTAMP DETAILS
UPDATED 123456TIMESTAMP DELTA
Request
Append new record with DELTA
Global event ID
Some code describing the operation
Timestamp
Entity identifier
Changes applied
Information
Transparent storage: relational, NoSQL, graph
In some cases, you might want to store
the full state of the entity along with the
specific event information.
Event recordCurrent state of the
entity
DELETE Operations
CREATED 888998TIMESTAMP DETAILS
UPDATED 123456TIMESTAMP DELTA
DELETED 123456TIMESTAMP REASON
Request
Append new record to mark logical deletion
Global event ID
Code for the operation
Timestamp
Entity identifier
Optionally reasons of deletion
Information
Transparent storage: relational, NoSQL, graph
Quick Facts
Append-only working mode
Updates saved as the delta
Logical deletion Physical deletion exceptionally allowed but not in the
middle of the stream
REPLAY Operations
Grab all events by
entity IDCREATED 123456TIMESTAMP DETAILS
UPDATED 123456TIMESTAMP DELTA
64
92
Replay through all
events
public static T Replay<T>(String id, IEnumerable<BaseEvent> events){
var aggregate = new T();foreach (var e in events){
if (e is AggregateCreatedEvent)aggregate.Create(e.Data);
if (e is AggregateUpdatedvent)aggregate.Update(e.Data);
if (e is AggregateDeletedEvent)aggregate.Delete(e.Data);
}return aggregate;
}}
Replay just selected events
Perform different calculations
Apply different forms of business logic
SCALABILITY POTENTIAL
Serialize the state of
aggregates to a given
point in time
SNAPSHOT
Replay events from a
given snapshot
TOOLS?
