We describe the challenges that we faced while building the instant search experience at LinkedIn, and present techniques that we developed to overcome them. We discuss three aspects of instant search – performance, tolerance to user errors, and accuracy of search results.

1. Fast, Lenient, and Accurate
Building Personalized Instant Search Experience at LinkedIn
Ganesh Venkataraman, Abhi Lad, Lin Guo, Shakti Sinha
LinkedIn

2. Agenda
● LinkedIn
● LinkedIn Search
○ Navigational vs Exploratory searches
○ Typeahead vs SERP
● Big picture and problem statement
● Instant search – Search-as-you-type
○ Query autocomplete
○ Entity-aware suggestions
○ Instant results
● Conclusions & Future work

3. LinkedIn – Professional Identity

4. LinkedIn – Professional Graph

5. LinkedIn – Jobs

6. LinkedIn – And much more...
Companies
Skills
Professional Content

7. LinkedIn – Massive Scale

8. LinkedIn Search

9. Navigational Search
Looking for someone specific
by name.
Query has a single correct
result.

10. Exploratory Search
Finding people that match a
given set of criteria.
Multiple results match the
user’s query.

11. Instant Search – Search-as-you-type
Satisfy navigational searches:
Show instant search results.
Help frame exploratory searches:
Complete the user’s query and show search suggestions.

12. Big Picture
Partial query
Instant results Autocomplete
Search suggestions
Query tagger
Full-text search
Search results
Manually
entered
query

13. Big Picture
Partial query
Instant results Autocomplete
Search suggestions
Query tagger
Full-text search
Search results
Manually
entered
query
Focus today:
● Autocomplete
● Search suggestions
● Instant results

14. Problem Statement
Partial query
Instant results Autocomplete
Search suggestions
Query tagger
Full-text search
Search results
Manually
entered
query
Focus today:
● Autocomplete
● Search suggestions
● Instant results
How can we build an instant search experience that scales to 450+ million members, and is
fast, lenient, and accurate?
● Instant search = Query autocomplete + search suggestions + instant results
● Fast = Search-as-you-type latencies
● Lenient = Handle spelling errors and common variations
● Accurate = Highly relevant and personalized results

15. Query Tagging
PERSON
TITLE
(ID=126)
COMPANY
(ID=1337)
Entity types identified:
Person name, job title, company, school, skills, locations.
Key part of query processing!
Impacts: autocomplete, spelling correction, search suggestions,
query rewriting, ranking.
Sequential prediction model
(CRF – Conditional Random Fields)
Training data:
● Standardized dictionaries (people names,
companies, schools, titles, skills, locations)
● Query logs
● Clickthrough (CTR) data
● Crowdsourced labels

16. Query Autocomplete
● Fast
● Relevant and contextual
● Resilient to spelling errors

17. Query Autocomplete – Offline processing
linkedin software engineer
software engineer
big data
data scientist
data engineer
expert systems
.
.
[linkedin] [software engineer]
Query logs Entities Index
FST – Finite State Transducers
Compact + fast retrieval + fuzzy match (via Levenstein Automata)

18. Query Autocomplete – Online processing
Two step process:
1. Retrieval (Candidate generation)
User’s query: [big data e]
Candidates = C(big data e) U C(data e) U C(e)
= big data engineer,
big data expert systems,
big data entry,
...
linkedin software engineer
software engineer
big data
data scientist
data engineer
expert systems
.
.
Query logs

19. Query Autocomplete – Online processing
Two step process:
2. Scoring (Ranking)
User’s query: [big data e]
Candidate completions: “big data engineer”, “big data expert”, “big data entry”
Score(“big data engineer”):
P(s1
, s2
, s3
…) ≈ P(s1
)·P(s2
|s1
)·P(s3
|s2
).. // Bigram language model
Use entities : P([engineer] | [big data])
Fall back to words : P(engineer | data)·P(data | big)

20. Query Suggestions – Autocomplete + query tagger
“linke” ⇒ “Linkedin” ⇒ COMPANY
“had” ⇒ “Hadoop” ⇒ SKILL

21. Instant Results
● Fast retrieval over 450+ million members
● Highly personalized
● Balance personalization & popularity
● Resilient to spelling variations

22. Instant Results – Indexing
NAME: richard
PREFIX: r, ri, ric, rich, richa, ...
NAME: branson
PREFIX: b, br, bra, bran, brans, ...
● Inverted Index (Maps token to list of docs that contain that token):
NAME:richard => [1, 4, 10, 15, …] // Everyone named “richard”
PREFIX:ri => [1, 2, 4, 7, 10, 15, …] // Everyone whose name starts with “ri”
…
● Retrieval approach
User’s query – richard b
Rewritten query – +NAME:richard +PREFIX:b
● Prefix-based tokenization:
DOCID 4
(posting lists)

23. Instant Results – Indexing
CONN: 1, 10, 15
● Inverted Index
CONN:4 => [1, 10, 15] // Everyone connected to Richard Branson
CONN:1 => [4, ...]
CONN:10 => [4, ...]
...
● Retrieval approach
User’s query – richard b
Rewritten query – +NAME:richard +PREFIX:b +CONN:1
(Everyone named richard b… and connected to User:1)
● Connections Index:
DOCID 4

24. Instant Results – Indexing
Early Termination
Problem: A query like [PREFIX:ri] might retrieve too many candidate documents.
How can we retrieve the most promising documents first so that we don’t need to score all of them?
Static Rank: Order documents based on their prior (query independent) likelihood of relevance:
A combination of:
● Profile views
● Spam and security related scores
● Editorial rules (Celebrities, influencers, …)
numToScore: The number of documents to retrieve and score for any query

25. Balancing Popularity and Personalization
Query: richard b…
Are you looking for Richard Branson, or a colleague name Richard Burton?
(Assume searcher’s ID = 1)
Rewritten Query:
● +NAME:richard +PREFIX:b +CONN:1 // Too restrictive. Only find searcher’s connections.
● +NAME:richard +PREFIX:b ?CONN:1[50%] // Try to retrieve 50% results from searcher’s connections
Instant Results – Retrieval
Custom search operator: “Weighted OR”

26. Instant Results – Spelling Variations
weiner ⇔ wiener
catherine ⇔ kathryn
dipak ⇔ deepak

27. Name Clusters
Offline process to cluster together similar sounding or similarly spelt names.
Two step process:
1. Coarse clustering (optimized for broad coverage)
Normalization: repeated chars, accented chars, common phonetic variations (c ⇔ k, ph ⇔ f)
Combination of edit distance & double metaphone (sound)
E.g. (dipak = deepak), (wiener = weiner), (catherine = kathryn), (jeff = joff)
2. Fine-grained clustering (optimized for precision)
Split up clusters based on more sophisticated rules
Position and character-aware edit distance
Query reformulation data (q1
→ q2
→ click)
E.g. (jeff ≠ joff)
Instant Results – Spelling Variations

28. Instant Results – Spelling Variations
NAME: kathryn
CLUSTER: katharine
Potential queries:
katherine
kathryn
katharine
catharine
Rewritten queries:
?NAME:katherine ?CLUSTER:katharine
?NAME:kathryn ?CLUSTER:katharine
?NAME:katharine ?CLUSTER:katharine
?NAME:catharine ?CLUSTER:katharine
Either match original query term or match the name cluster
Query time
Indexing time

29. Clicked result treated as positive.
All other shown results treated as negative.
Since this is navigational search, we assume there’s
only 1 correct result => low presentation bias.
Learning to Rank (Machine-learned ranking)
Training data
● Click data from previous typeahead sessions
● <searcher, query, doc> ⇒ positive/negative
Features / signals
● Textual match against various fields
● Network distance, number of shared connections
● Global popularity
● Compound features
Instant Results – Scoring
+
–
–
–

30. Conclusions
● Instant search experience
○ Directly satisfy navigational search uses in typeahead via Instant Results
○ Help the user frame exploratory search queries via Query Autocomplete & Search
Suggestions
● Combination of techniques
○ Query tagger for entity extraction – “Things not Strings”
○ FST-based query completion
○ Inverted index-based instant results + Early termination + Weighted OR
○ Name clusters for fuzzy name matching

31. Future Work
● Personalized query completions
○ m ⇒ machine learning
○ m ⇒ machinist
● Multi-entity query suggestions
○ Now : [linkedin] ⇒ “Find people who work at LinkedIn”
○ Future : [linkedin data scientist] ⇒ “Find data scientists at LinkedIn”
● Better blending
○ Autocomplete + query suggestions + instant results
○ Query features – what does the query mean?
○ Results features – what results come back from each system?

32. Thank You!

33. LinkedIn – The Economic Graph

34. LinkedIn Search – SERP (Jobs)

35. LinkedIn Search – Typeahead

36. LinkedIn Search – SERP