Deep dive to ElasticSearch - معرفی ابزار جستجوی الاستیکی

NoSQL doesn’t mean no data
• It’s not Anti SQL or absolutely no SQL
• N(ot) O(nly) SQL
• Non-relational Databases
Why not SQL?
• Internet scale
• 100s of millions of concurrent users
• Massive data collections –
Terabytes to Petabytes of data
• 24/7 across the globe
What is NoSQL good for? BIG DATA
• High Availability
• High Performance
• Horizontal Scalability

‌‫‌های‌افزایش‌توان‬‫ه‬‫را‬‫پردازش‬
(‫توسعه‌عمودی‌یا‌افقی‬)

• Consistency - This means that all nodes see the same data at the same time.
• Availability - This means that the system is always on, no downtime.
• Partition Tolerance - This means that the system continues to function even if the
communication among the servers is unreliable
•SQL - CA
•NoSQL - AP
CAP theorem (Consistency, Availability and Partition-tolerance)

NoSQL ACID Trade-offs
• Dropping Atomicity lets you shorten the time tables (sets
of data) are locked.
MongoDB, CouchDB.
• Dropping Consistency lets you scale up writes across
cluster nodes.
Riak, Cassandra.
• Dropping Durability lets you respond to write commands
without flushing to disk.
Memcache, Redis.

ACID vs. BASE
• ACID:
• Atomic: Every transaction should succeed else transaction is rolled back
• Consistent: Every transaction leaves database in a valid (consistent) state
• Isolation: Transactions don’t interfere with each other
• Durable: Completed transactions persist, even when servers restart

ACID vs. BASE
• BASE
• Basic Availability: The data store should be up all of the time
• Soft state: The data store can be cached somewhere else if the data
store is not available
• Eventual consistency: The data store can have conflicting
transactions, but should eventually reach a valid state

Different types of NOSQL
Key-Value Store
• A key that refers to a payload
• MemcacheDB, Azure Table Storage, Redis
Graph Store
• Nodes are stored independently, and the relationship between
nodes (edges) are stored with data
• Neo4j
Column Store
• Column data is saved together, as opposed to row data
• Super useful for data analytics
• Cassandra, Hypertable
Document / XML / Object Store
• Key (and possibly other indexes) point at a serialized object
• DB can operate against values in document
• MongoDB, CouchDB, RavenDB, ElasticSearch

NoSQL document example
{
"_id": ObjectId,
"description": String,
"total": Number,
"notes": [{
"_id": ObjectId,
"text": String
}],
"exclusions": [{
"_id": ObjectId,
"text": String
}],
"categories": {
"ref1": {
"name": String,
"status": String,
"price": Number
},
"ref2": {
"name": String,
"status": String,
"price": Number
}
}
}
ORM (Object-relational mapping)
● Entity Framework (.NET)
● Hibernate (Java)
● Django (Python)
● Sequelize (JS) is an ORM for Node.js and io.js
j = { name : "mongo" }
k = { x : 3 }
db.things.insert( j )
db.things.insert( k )
db.things.find()
{"_id" : ObjectId("4c2209f9f3924d31102bd84a"), "name" :
"mongo"}
{"_id" : ObjectId("4c2209fef3924d31102bd84b"), "x" : 3 }
ODM (Object Data Manager)
● Mongoose (Mongo)

Use SQL if:
● Data integrity is essential
● Standards-based proven technologies with good developer
experience and support
● Logical related discrete data requirements which can be identified
up-front
● Prefer SQL

Use NoSQL if:
● Data requirements are unrelated, indeterminate or evolving
● Project objectives are simpler of less specific and allow starting to
code immediately
● Speed and scalability is imperative
● Prefer NoSQL

SQL Products and customers
December, 2015

‫های‬‫داده‬ ‫پایگاه‬ ‫مزایای‬NoSql:
o‫اطالعات‬ ‫درج‬ ‫بیشتر‬ ‫سرعت‬
o‫مقیاس‬‫پذیر‬(‫داده‬ ‫های‬‫بخش‬ ‫مدیریت‬)‫راحت‬ ‫گسترش‬ ‫امکان‬ ‫و‬‫تر‬
o‫برای‬ ‫شده‬ ‫بهینه‬ ‫و‬ ‫مناسب‬‫مختلف‬ ‫های‬‫قالب‬ ‫و‬ ‫خاص‬ ‫کاربردهای‬‫داده‬
o‫پذیری‬‫انعطاف‬(Flexibility)‫بدلیل‬ ‫باال‬Schemaless‫در‬ ‫که‬ ‫بودن‬
‫ساختار‬ ‫تغییر‬ ‫نتیجه‬(‫ها‬‫ویژگی‬)‫است‬ ‫ساده‬ ‫داده‬ ‫پایگاه‬ ‫در‬ ‫ها‬‫داده‬.
o‫شیءگرایی‬ ‫از‬ ‫استفاده‬ ‫با‬ ‫ها‬‫داده‬ ‫به‬ ‫دسترسی‬(‫جداگ‬ ‫زبان‬ ‫به‬ ‫نیازی‬‫انه‬
‫مانند‬SQL‫ندارند‬ ‫داده‬ ‫تغییر‬ ‫و‬ ‫دسترسی‬ ‫برای‬)
oOpen source‫آنها‬ ‫اغلب‬ ‫بودن‬
‫های‬‫داده‬ ‫پایگاه‬ ‫ضعف‬ ‫نقاط‬NoSql:
o‫از‬ ‫آنها‬ ‫پشتیبانی‬ ‫عدم‬‫تمام‬‫ویژگی‬‫های‬ACID
o‫است‬ ‫دشوار‬ ‫ها‬‫داده‬ ‫سازگاری‬ ‫کنترل‬
o‫نامناسب‬‫برای‬join‫داده‬‫ها‬
o‫بازیابی‬ ‫سرعت‬(select)‫های‬‫داده‬‫متوسط‬ ‫حجم‬(‫سازمانی‬ ‫های‬‫داده‬)‫روی‬ ‫بر‬
‫یک‬node(‫تک‬ ‫سرور‬)‫عادی‬ ‫و‬(‫ایندکس‬‫شده‬)‫های‬‫داده‬ ‫پایگاه‬ ‫به‬ ‫نسبت‬
‫هست‬ ‫تر‬‫پایین‬ ‫مالحظه‬ ‫قابل‬ ‫بطور‬ ‫ای‬‫رابطه‬.
o‫از‬ ‫پشتیبانی‬ ‫عدم‬trigger
A well-designed SQL database will almost certainly perform better than a badly designed NoSQL equivalent and vice versa.

NoSql Database Type Comparison
Data Model Performance Scalability Flexibility Complexity
Key–Value Store high high high none
Column-Oriented Store high high moderate low
Document-Oriented Store high variable (high) high low
Graph Database variable variable high high
Relational Database variable variable low moderate

Summary
SQL - works great, isn’t scalable for large data 😞
NoSQL - works great, isn’t suitable for everyone 😞
SQL + NoSQL 😊

• Efficient indexing of data
• On all fields / combination of fields
• Analyzing data
• Text Search
• Tokenizing
• Stemming
• Filtering
• Understanding locations
• Date parsing
• Relevance scoring
What is a search engine?

• Finding word boundaries
• Not just explode(‘ ‘, $text);
• Chinese has no spaces. (Not every single character is a word.)
• Understand patterns:
• URLs
• Emails
• #hashtags
• Twitter @mentions
• Currencies (EUR, €, …)
Tokenizing

• “Stemming is the process for reducing inflected (or sometimes derived)
words to their stem, base or root form.”
• Conjugations
• Plurals
• Example:
• Fishing, Fished, Fish, Fisher > Fish
• Better > Good
• Several ways to find the stem:
• Lookup tables
• Suffix-stripping
• Lemmatization
• …
• Different stemmers for every language.
Stemming

Filtering
• Remove stop words
• Different for every language
• HTML
• If you’re indexing web content, not every character is
meaningful.

Understanding locations
• Reverse geocoding of locations to longitude & latitude
• Search on location:
• Bounding box searches
• Distance searches
• Searching nearby
• Geo Polygons
• Searching a country
•(Note: Relational DBs also have geospatial indeces.)

Relevance Scoring
• From the matched documents, which ones do you show first?
• Several strategies:
• How many matches in document?
• How many matches in document as percentage of length?
• Custom scoring algorithms
• At index time
• At search time
• … A combination
Think of Google PageRank.

Apache lucene
•“Information retrieval software library”
•Free/open source
•Supported by Apache Foundation
•Created by Doug Cutting
•Written in 1999
•The latest version of Lucene is 6.5.0 which was released on March 27, 2017.
“There’s software a Java library for that.”

Comparing MS SQL Full Text Search and Lucene
Lucene MS SQL FTS
Index auto update No Yes
Store data in index Yes No
Location in RAM Yes No
Interface API SQL
Queering multiple columns Yes Yes
Stop words, synonyms, sounds-like Yes Yes
Custom Index Documents Structure Yes No
Wildcards Yes With restrictions
Spellchecking, hit-highlighting and other extensions
Provided in “contrib”
extensions library
No

Comparing MS SQL Full Text Search and Lucene
Lucene MS SQL FTS
Indexing Speed 3 MB/sec 1 MB/sec
Index Size 10-25% 25-30%
Simple query <20 ms < 20 ms
Query With
Custom Score
< 4 sec >20 sec
MS SQL FTS Lucene (File System) Lucene (RAM)
Cold System
Simple Query 56 643 21
Complex Query 19669* 859 27
Second
executions
Simple Query 14 8 <5
Complex Query 465 17 9
Indexing speed, size and single query execution time
Parallel Query Executions (10 threads, average execution time per query in ms)

Elasticsearch
• ElasticSearch is a free and open source distributed inverted index.
• Built on top of Lucene
 Lucene is a most popular java-based full text search index implementation.
• Created by Shay Banon @kimchy
• Versions
 First public release, v0.4 in February 2010
 Now stable version at 5.3.0 (March 28, 2017)
• In Java, so inherently cross-platform
• Repository : github.com/elastic/elasticsearch
• Website : www.elastic.co/products/elasticsearch

Why ElasticSearch?
 Easy to scale (Distributed)
 Everything is one JSON call away (RESTful API)
 Unleashed power of Lucene under the hood
 Excellent Query DSL
 Multi-tenancy (multi cluster, node, shards)
 Support for advanced search features (Full Text)
 Configurable and Extensible
 Document Oriented
 Schema free
 Conflict management (Optimistic Concurrency Control using Versioning)
 Active community

 ElasticSearch is built to scale horizontally out of the box.
When ever you need to increase capacity, just add more
nodes, and let the cluster reorganize itself to take advantage
of the extra hardware.
 One server can hold one or more parts of one or more
indexes, and whenever new nodes are introduced to the
cluster they are just being added to the party. Every such
index, or part of it, is called a shard, and ElasticSearch shards
can be moved around the cluster very easily.
Easy to Scale (Distributed)
RESTful API
 ElasticSearch is API driven. Almost any action can be performed
using a simple RESTful API using JSON over HTTP. .
 Responses are always in JSON format.

 Apache Lucene is a high performance, full-featured
Information Retrieval library, written in Java. ElasticSearch uses
Lucene internally to build its state of the art distributed search
and analytics capabilities.
 Since Lucene is a stable, proven technology, and continuously
being added with more features and best practices, having
Lucene as the underlying engine that powers ElasticSearch.
Build on top of Apache Lucene
Excellent Query DSL (Domain Specific Language)
 The REST API exposes a very complex and capable query DSL, that is
very easy to use. Every query is just a JSON object that can practically
contain any type of query, or even several of them combined.
 Using filtered queries, with some queries expressed as Lucene filters,
helps leverage caching and thus speed up common queries, or complex
queries with parts that can be reused.
 Faceting, another very common search feature, is just something that
upon-request is accompanied to search results, and then is ready for
you to use.

 Multiple indexes can be stored on one ElasticSearch
installation - node or cluster. Each index can have
multiple "types", which are essentially completely
different indexes.
 The nice thing is you can query multiple types and
multiple indexes with one simple query.
Multi-tenancy
Support for advanced search features (Full Text)
 ElasticSearch uses Lucene under the covers to provide the most
powerful full text search capabilities available in any open source
product.
 Search comes with multi-language support, a powerful query
language, support for geolocation, context aware did-you-mean
suggestions, autocomplete and search snippets.
 Script support in filters and scorers

 Many of ElasticSearch configurations can be changed while ElasticSearch is running, but some will require a
restart (and in some cases re-indexing). Most configurations can be changed using the REST API too.
 ElasticSearch has several extension points - namely site plugins (let you serve static content from ES - like
monitoring java script apps), rivers (for feeding data into ElasticSearch), and plugins to add modules or
components within ElasticSearch itself. This allows you to switch almost every part of ElasticSearch if so you
choose, fairly easily.
Configurable and Extensible
Document Oriented
 Store complex real world entities in ElasticSearch as structured
JSON documents. All fields are indexed by default, and all the
indices can be used in a single query, to return results at breath
taking speed.
Per-operation Persistence
 ElasticSearch primary moto is data safety. Document changes are
recorded in transaction logs on multiple nodes in the cluster to
minimize the chance of any data loss.

 ElasticSearch allows you to get started easily. Send a
JSON document and it will try to detect the data
structure, index the data and make it searchable.
Schema free
Conflict management
 Optimistic version control can be used where
needed to ensure that data is never lost due to
conflicting changes from multiple processes.
Active community
 The community, other than creating nice tools and plugins, is very helpful and supporting.
The overall vibe is really great, and this is an important metric of any OSS project.
 There are also some books currently being written by community members, and many blog
posts around the net sharing experiences and knowledge

Terminology
SQL Elastic Search
Database Index
Table Type
Row Document
Column Field
Schema Mapping
Index Everything is indexed
SQL Query DSL
SELECT * FROM table … GET http://…
UPDATE table SET … PUT http://…

Who is using https://www.elastic.co/use-cases

What Does It Add To Lucene?
• RESTfull Service
• JSON API over HTTP
• Want to use it from .Net, Python, PHP, …?
• CURL Requests, as if you’d do requests to the Facebook Graph API.
• High Availability & Performance
• Clustering
• Distributed system on top of Lucene
• Provides other supporting features like thread pool, queues, node/cluster
monitoring API ,data monitoring API ,Cluster management etc.

… vs. SOLR
• +
• Also built on Lucene
• So similar feature set
• Also exposes Lucene functionality, like Elastic Search, so easy to
extend.
• A part of Apache Lucene project
• Perfect for Single Server search
• -
• ElasticSearch is easier to use and maintain
• Clustering is there. But it’s definitely not as simple as ElasticSearch’
• Fragmented code base. (Lots of branches.)

Configuration
 cluster.name:Clusternameidentifiesclusterforauto-discovery.Ifproductionenvironmenthasmultipleclustersonthe
samenetwork,clusternamemustbeunique.
 node.name:Nodenamesaregenerateddynamicallyonstartup.Butusercanspecifyanametonodemanually.
 node.master &node.data:Everynodecanbeconfiguredtoallowordenybeingeligibleasthemaster,andtoallowor
denytostorethedata.Masterallowthisnodetobeeligibleasamasternode(enabledbydefault)andDataallowthis
nodetostoredata(enabledbydefault).
Followingarethesettingstodesignadvancedclustertopologies.
1. Ifanodetoneverbecomeamasternode,onlytoholddata.Thiswillbethe"workhorse"ofthecluster.
node.master:false,node.data:true
2. Ifanodetoonlyserveasamasterandnottostoredataandtohavefreeresources.Thiswillbethe"coordinator"
ofthecluster. node.master:true,node.data:false
3. Ifanodetobeneithermasternordatanode,but toactasa"searchloadbalancer"(fetchingdatafromnodes,
aggregating,etc.)
node.master:false,node.data:false

Configuration
 Index:Anumberofoptions(suchasshard/replicaoptions,mappingoranalyzerdefinitions,translogsettings,...)canbe
setforindicesglobally,inthisfile.Note,thatitmakesmoresensetoconfigureindexsettingsspecificallyforacertain
index,eitherwhencreatingitorbyusingtheindextemplatesAPI..
example.index.number_of_shards:5,index.number_of_replicas:1
 Discovery:ElasticSearchsupportsdifferenttypesofdiscovery,whichimakesmultipleElasticSearchinstancestalktoeach
other.
Thedefaulttypeofdiscoveryismulticast. Unicastdiscoveryallowstoexplicitlycontrolwhichnodeswillbeusedto
discoverthecluster.Itcanbeusedwhenmulticastisnotpresent,ortorestricttheclustercommunication-wise.

 Cluster
 logical grouping of multiple nodes
 Nodes in cluster that store data or nodes that just help in speeding up search queries.
 Node
 An elasticsearch server instance
 Usually you should have one node per server
 Master – in charge of managing cluster-wide operations
 Only one, responsible for distribution/balancing of shards
 No bottleneck for queries
 Master node is chosen automatically by the cluster
 Shard
 A shard in elasticsearch is a Lucene index, and a Lucene index is broken down into segments.
 low-level worker instance that holds a slice of all data
 Each document belongs to a single primary shard
 Created during index creation
 Determines the number of data stored in each shard
 Replica
 A copy of a master shard on a different node (increase failover + increase [search] performance)
 Automatic Master detection + failover
 Spreading over nodes => done automatically
 Can be created any time
Scalability - Architecture

Is it running?
http://localhost:9200/?pretty
Response:
{
"status" : 200,
"name" : “elasticsearch",
"version" : {
"number" : "1.3.4",
"build_hash" : "f1585f096d3f3985e73456debdc1a0745f512bbc",
"build_timestamp" : "2015-04-21T14:27:12Z",
"build_snapshot" : false,
"lucene_version" : "4.9"
},
"tagline" : "You Know, for Search"
}

Indexing a document
Request:
PUT test/cities/1
{
"rank": 3,
"city": "Hyderabad",
"state": "Telangana",
"population2014": 7750000,
"land_area": 625,
"location":
{
"lat": 17.37,
"lon": 78.48
},
"abbreviation": "Hyd"
}
Response:{ "_index": "test", "_type": "cities", "_id": "1", "_version": 1, "created": true }

Getting a document
Request:
GET test/cities/1?pretty
Response:
{
"_index": "test",
"_type": "cities",
"_id": "1",
"_version": 1,
"found": true,
"_source": {
"rank": 3,
"population2014": 7750000,
"land_area": 625,
"location": {
"lat": 17.37,
"lon": 78.48
},
}
}

Updating a document
Request:
PUT test/cities/1
{
"rank": 3,
"population2013": 7023000,
"population2014": 7750000,
"land_area": 625,
"location":
{
"lat": 17.37,
"lon": 78.48
},
}
Response:{"_index": "test", "_type": "cities", "_id": "1", "_version": 2, "created": false}

Data Synchronization
 Elastic search is typically not the primary data store.
 Implement a queue or use rivers or window service.
 A river is a pluggable service running within elasticsearch cluster pulling data (or being pushed with data)
that is then indexed into the cluster. (https://github.com/jprante/ElasticSearch-river-jdbc)
Rivers are available for mongodb, couchdb, rabitmq, twitter, wikipedia, mysql, and etc
The relational data is internally transformed into structured JSON objects for the schema-less
indexing model of ElasticSearch documents.
The plugin can fetch data from different RDBMS source in parallel, and multithreaded bulk mode
ensures high throughput when indexing to ElasticSearch.
 TypicallyElasticSearchimplementsworkerroleasalayerwithintheapplicationtopushdata/entitiestoElasticsearch.

Products (Open Source + Commercial)

Kibana
•Powerful front-end dashboard for visualizing indexed information from elastic cluster.
•Capable to providing historical data in form of graphs, charts, etc.
•Enables real-time search of indexed information.
Data Visualization + Data Discovery

REST API
Analysis
chain
Search
Querying
Query
parser
Lucene Index
Perform
indexing
Indexing
Make Lucene
document
ElasticsearchServer

Lucene extension points
Analysis chain
Search
Query parser
Lucene Index
Perform indexing

Harry Potter and the Goblet of Fire
Tokenizer
Harry
Potter
and
the
Goblet
of
Fire
Lower case
filter
harry
potter
and
the
goblet
of
fire
Stop-words
filter
harry
potter
goblet
fire
Step 1: Tokenization
Step 2: Filtering

Welcome to Malmö!
Tokenizer
Welcome
to
Malmö
ASCII folding
filter
Lowercase
filter
Step 1: Tokenization
Step 2: Filtering
Welcome
to
Malmo
welcome
to
malmo

Harry Potter and the Goblet of Fire
Tokenizer
Harry
Potter
and
the
Goblet
of
Fire
Lower case
filter
harry
potter
and
the
goblet
of
fire
Stop-words
filter
harry
potter
goblet
fire
Potter
Tokenizer
Potter
Lower case
filter
potter
Stop-words
filter
potter
QueryIndexing

Analyzers
The quick brown fox jumped over the lazy dog,
bob@hotmail.com 123432.
StandardAnalyzer:
[quick] [brown] [fox] [jumped] [over] [lazy] [dog] [bob@hotmail.com] [123432]
StopAnalyzer:
[quick] [brown] [fox] [jumped] [over] [lazy] [dog] [bob] [hotmail] [com]
SimpleAnalyzer:
[the] [quick] [brown] [fox] [jumped] [over] [the] [lazy] [dog] [bob] [hotmail]
[com]
WhitespaceAnalyzer:
[The] [quick] [brown] [fox] [jumped] [over] [the] [lazy] [dog,]
[bob@hotmail.com] [123432.]
KeywordAnalyzer:
[The quick brown fox jumped over the lazy dog, bob@hotmail.com 123432.]

Custom scoring & similarity
• Function score query
• Previously known as Custom Score Query
• Similarity

What is NEST?
NEST
• All request & response objects represented
• Strongly typed Query DSL implementation
• Supports fluent syntax
• Uses ElasticSearch.net
ElasticSearch.NET
• Low-level, dependency-free client
• All ES endpoints are available as methods
ElasticSearch RESTFul API
http://nest.azurewebsites.net/

NEST – Connection Initialization
• Initialize an ElasticClient:
All actions on the ElasticSearch cluster are performed using the ElasticClient
For example:
• Search
• Index
• DeleteIndex/CreateIndex
• …
Uri node = new Uri("http://192.168.137.73:9200");
ConnectionSettings settings = new ConnectionSettings(node, defaultIndex: "products");
ElasticClient client = new ElasticClient(settings);

Index your Content - .NET
• Raw JSON string
• Type based indexation
• Modify out-of-the-box behavior using decorators
client.Raw.Index("products", "product", new JavaScriptSerializer().Serialize(prod));
client.Index(product);
[ElasticType(Name = "Product", IdProperty="id")]
public class Product
{
public int id { get; set; }
[ElasticProperty(Name = "name", Index = FieldIndexOption.Analyzed, Type = FieldType.String, Analyzer = "standard")]
public string name { get; set; }
…

Query your content – Query DSL .NET
• Retrieve all products from an index using a MatchAll search
• Retrieve all products by using a term query
• Search on all fields using the _all built-in property
• Search on a combination of fields using boolean operators (see fiddler result)
result = client.Search<Product>(s => s.MatchAll());
result = client.Search<Product>(s => s.Query(q => q.Term(t => t.name, "macbook")));
result = client.Search<Product>(s => s.Query(q => q.Term("name", "macbook")));
result = client.Search<Product>(s => s.Query(q => q.Term("_all", "macbook")));
result = client.Search<Product>(s => s.Query(q => q.Term("name", "macbook") ||
q.Term("descr","macbook")));

Query your content – Query DSL
• Search on a combination of fields using boolean operators and a date range
filter
• Some more advanced query examples:
• Wildcard Query - use wildcards to search for relevant documents
• Span Near - search for word combinations within a certain span in the document
• More like this query - finds documents which are ‘like’ a given set of documents using
representative terms
result = client.Search<Product>(s => s
.Query(q => (q.Term("name", "macbook") || q.Term("descr", "macbook"))
&& q.Range(r => r
.OnField("price")
.Greater(1000)
.LowerOrEquals(2000)
)));

Query your content – Fuzzy searches
• Perform a fuzzy search to overcome query string errors
.Query(q => q
.Match(m => m
.Query("makboek")
.OnField("name")
.Fuzziness(10)
.PrefixLength(1)
)));

Query your content - Paging
• Select pages from the full result set using the From & Size filters
.Query(q => q.Term("name", "macbook") || q.Term("descr", "macbook"))
.From(0)
.Size(1));

http://www.elastic.co/guide/en/elasticsearch/guide/current/index.html
http://www.elasticsearchtutorial.com/
http://lucene.apache.org/
Lucene in Action
SlideShare.net presentations on ElasticSearch
References

Deep dive to ElasticSearch - معرفی ابزار جستجوی الاستیکی

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