Solr provides concise summaries of key points from the document: 1. Solr discusses its search architecture including the use of Thrift for service encapsulation and reduced network traffic. Only IDs are returned from searches to reduce index size and enable easy scaling of primary key lookups. 2. Load balancing is discussed, including an algorithm that hashes the query and number of servers to provide server affinity while distributing load evenly. 3. Replication of the index is covered, including challenges with multicast and an implementation using BitTorrent to efficiently replicate files.

1. Solr@

2. Things I’m not going to
talk about:
A/B Testing
i18n
Continuos Deployment

3. About
Us

6. 10+ Million Listings
500 qps

7. Architecture
Overview

8. Architecture Overview
Thrift

9. Architecture Overview
Thrift
struct Listing {
1: i64 listing_id
}
struct ListingResults {
1: i64 count,
2: list<Listing> listings
}
service Search {
ListingResults search(1:string query)
}

10. Architecture Overview
Thrift
Generated Java server code:
public class Search {
public interface Iface {
public ListingResults search(String query) throws TException;
}
Generated PHP client code:
class SearchClient implements SearchIf {
/**...**/
public function search($query)
{
$this->send_search($query);
return $this->recv_search();
}

11. Architecture Overview
Thrift
Why use Thrift?
• Service Encapsulation
• Reduced Network Traffic

12. Architecture Overview
Thrift
Why only return IDs?
• Index Size
• Easy to scale PK lookups

13. The Search Server

14. Architecture Overview
Search Server
• Identical Code + Hardware
• Roles/Behavior controlled by Env variables
• Single Java Process
• Solr running as a Jetty Servlet
• Thrift Servers
• Smoker

15. Architecture Overview
Search Server
Master-specific processes:
• Incremental Indexer
• External File Field Updaters

16. Load Balancing

17. Load Balancing
Thrift TSocketPool

18. Load Balancing
Thrift TSocketPool

19. Load Balancing
Thrift TSocketPool

20. Load Balancing
Server Affinity

21. Load Balancing
Server Affinity Algorithm
$serversNew = array();
[“host2”, “host3”, “host1”, “host4”]
$numServers = count($servers);
while($numServers > 0) {
// Take the first 4 chars of the md5sum of the server count
// and the query, mod the available servers
$key = hexdec(substr(md5($numServers . '+' . $query),0,4))%($numServers);
$keySet = array_keys($servers);
$serverId = $keySet[$key];
// Push the chosen server onto the new list and remove it
// from the initial list
array_push($serversNew, $servers[$serverId]);
unset($servers[$serverId]);
--$numServers;
}

22. Load Balancing
Server Affinity Algorithm
$key = hexdec(substr(md5($query),0,4))
“jewelry” [“host2”, “host3”, “host1”, “host4”]
“scarf” [“host2”, “host3”, “host1”, “host4”]

23. Load Balancing
Server Affinity Algorithm
$key = hexdec(substr(md5($numServers . '+' . $query),0,4))%(count($servers));
“jewelry” [“host2”, “host3”, “host1”, “host4”]
“scarf” [“host2”, “host1”, “host4”, “host3”]

24. Load Balancing
Server Affinity Results
2% 20%

25. Load Balancing
Server Affinity Caveats
• Stemming / Analysis
• Be wary of query distribution

26. Replication

27. Replication
The Problem

28. Replication
The Problem

29. Replication
Multicast Rsync?

30. Replication
Multicast Rsync?
[15:25] <engineer> patrick: i'm gonna test multi-rsyncing some indexes
from host1 to host2 and host3 in prod. I'll be watching the graphs and
what not, but let me know if you see anything funky with the network
[15:26] <patrick> ok
....
[15:31] <keyur> is the site down?

31. Replication
Multicast Rsync?

32. Hmm...Bit Torrent?

33. Replication
Bit Torrent POC
Using BitTornado:

34. Replication
Bit Torrent + Solr
Fork of TTorent: https://github.com/etsy/ttorrent
Multi-File Support
Performance Enhancements

35. Replication
Bit Torrent + Solr

36. Replication
Bit Torrent + Solr

37. Replication
Bit Torrent + Solr

38. Replication
Bit Torrent + Solr

39. Solr InterOp

40. QParsers

41. “writing query strings
is for suckers”

43. Solr InterOp
QParsers
http://host:8393/solr/person/select/?q=_query_:%22{!dismax
%20qf=$fqf%20v=$fnq}%22%20OR%20(_query_:%22{!dismax%20qf=$fiqf
%20v=$fiq}%22%20AND%20(_query_:%22{!dismax%20qf=$lwqf%20v=$lwq}
%22%20OR%20_query_:%22{!dismax%20qf=$lqf%20v=$lq}%20%22))&fnq=
%22giovanni%20fernandez-kincade
%22&fqf=full_name^4&fiq=giovanni&fiqf=first_name^2.0%20first_name_s
yn&qt=standard&lwq=fernandez-kincade*&lwqf=last_name&lq=fernandez-
kincade&lqf=last_name^3

44. Solr InterOp
QParsers
http://host:8393/solr/person/select/?q={!personrealqp}giovanni
%20fernandez-kincade

45. Solr InterOp
QParsers
class PersonNameRealQParser extends QParser {
public PersonNameRealQParser(String qstr, SolrParams localParams,
SolrParams params, SolrQueryRequest req) {
super(qstr, localParams, params, req);
}

46. Solr InterOp
QParsers
@Override
public Query parse() throws ParseException {
TermQuery exactFullNameQuery = new TermQuery(new Term("full_name", qstr));
exactFullNameQuery.setBoost(4.0f);
String[] userQueryTerms = qstr.split("s+");
Query firstLastQuery = null;
if (2 == userQueryTerms.length)
firstLastQuery = parseAsFirstAndLast(userQueryTerms[0], userQueryTerms[1]);
else
firstLastQuery = parseAsFirstOrLast(userQueryTerms);
DisjunctionMaxQuery realNameQuery = new DisjunctionMaxQuery(0);
realNameQuery.add(exactFullNameQuery);
realNameQuery.add(firstLastQuery);
return realNameQuery;
}

47. Solr InterOp
QParsers
The QParserPlugin that returns our new QParser:
public class PersonNameRealQParserPlugin extends QParserPlugin {
public static final String NAME = "personrealqp";
@Override
public void init(NamedList args) {}
@Override
public QParser createParser(String qstr, SolrParams localParams,
SolrParams params, SolrQueryRequest req) {
return new PersonNameRealQParser(qstr, localParams, params, req);
}
}

48. Solr InterOp
QParsers
Registering the plugin in solrconfig.xml:
<queryParser name="personrealqp"
class="com.etsy.person.solr.PersonNameRealQParserPlugin" />

49. Custom Stemmer

50. Solr InterOp
Custom Stemmer

51. Solr InterOp
Custom Stemmer
banded, banding, birding, bouldering, bounded, buffing, bundler, canning,
carded, circled, coupler, dangler, doubler, firring, foiling, hooper, japanned,
lipped, napped, papered, pebbled, pitted, pocketed, reductive, ricer, rooter,
roper, seeded, shouldered, silvered, skinning, spindling, staining, stitcher,
strapped, threaded, yellowing

52. Solr InterOp
Custom Stemmer
First we extend KStemmer and intercept stem calls:
public class LStemmer extends KStemmer {
/**.....**/
@Override
String stem(String term) {
String override = overrideStemTransformations.get(term);
if(override != null) return override;
return super.stem(term);
}
}

53. Solr InterOp
Custom Stemmer
Then create a TokenFilter that uses the new Stemmer:
final class LStemFilter extends TokenFilter {
/**.....**/
protected LStemFilter(TokenStream input, int cacheSize) {
super(input);
stemmer = new LStemmer(cacheSize);
}
@Override
public boolean incrementToken() throws IOException {
/**....**/
}

54. Solr InterOp
Custom Stemmer
Create a FilterFactory that exposes it:
public class LStemFilterFactory extends BaseTokenFilterFactory {
private int cacheSize = 20000;
@Override
public void init(Map<String, String> args) {
super.init(args);
String cacheSizeStr = args.get("cacheSize");
if (cacheSizeStr != null) {
cacheSize = Integer.parseInt(cacheSizeStr);
}
}
@Override
public TokenStream create(TokenStream in) {
return new LStemFilter(in, cacheSize);
}
}

55. Solr InterOp
Custom Stemmer
And finally plug it into your analysis chain:
<analyzer>
<tokenizer class="solr.WhitespaceTokenizerFactory"/>
<filter class="solr.ASCIIFoldingFilterFactory"/>
<filter class="solr.StopFilterFactory" ignoreCase="true"
words="solr/common/conf/stopwords.txt"/>
<filter class="com.etsy.solr.analysis.LStemFilterFactory" />
<filter class="solr.RemoveDuplicatesTokenFilterFactory"/>
</analyzer>

56. Thanks!