Apache Solr

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This is a total rip-off post from my contribution to Stackoverflow on Apache Solr . This post begins from simple introduction to detailed installation and implementation.

Simple Introduction

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• Can Apache Solr be used for High Traffic based websites? Does it utilize more CPU resources?

Solr shouldn’t be used to solve real-time problems. For search engines, Solr is pretty much game and works flawlessly.

Solr works fine on High Traffic web-applications. It utilizes the RAM, not the CPU.

• How does Apache Solr scores with respect to results, relevance and ranking?

The boost helps you rank your results show up on top. Say, you’re trying to search for a name john in the fields firstname and lastname, and you want to give relevancy to the firstname field, then you need to boost up the firstname field as shown.

http://localhost:8983/solr/collection1/select?q=firstname:john^2&lastname:john

As you can see, firstname field is boosted up with a score of 2.

More on SolrRelevancy

• Can you tell me about the indexing speed of Apache Solr?

The speed is unbelievably fast and no compromise on that.

Regarding the indexing speed, Solr can also handle JOINS from your database tables. A higher and complex JOIN do affect the indexing speed. However, an enormous RAM configuration can easily tackle this situation.

The higher the RAM, the faster the indexing speed of Solr is.

• Can Apache Solr integrated with Django?

Never had a chance to attempt that, however you can achieve that with Haystack. I found some interesting article on the same and here’s the github for it.

• I have a question on resource requirements - My website will be hosted on a VPS, so ideally the search engine wouldn’t require a lot of RAM and CPU?

Solr breeds on RAM, so if the RAM is high, you don’t to have to worry about it.

Solr’s RAM usage shoots up on full-indexing if you have some billion of records, you could smartly make use of Delta Imports to tackle this situation. As explained, Solr is only a near real-time solution.

• Heard from sources that Solr does not possess scalability factor. Is it true?

Solr is highly scalable. Have a look on SolrCloud. Some key features of it.

• Shards (or sharding is the concept of distributing the index among multiple machines, say if your index has grown too large)
• Load Balancing (if Solrj is used with Solr cloud it automatically takes care of load-balancing using it’s Round-Robin mechanism)
• Distributed Search
• High Availability

• Does it have any extra features like Google does - such as “did you mean by?”, related searches, etc?

For the above scenario, you could use the SpellCheckComponent that is shipped with Solr. There are a lot other features, The SnowballPorterFilterFactory helps to retrieve records say if you typed, books instead of book, you will be presented with results related to book.

This answer broadly focuses on Apache Solr & MySQL.

Important: Assuming that you are under LINUX environment, you could proceed to this article further. (mine was an Ubuntu 14.04 version). Windows users. Sorry.

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Detailed Installation

Getting Started

Download Apache Solr from here. That would be version is 4.8.1. You could download new versions, I found this one pretty stable.

After downloading the archive, extract it to a folder of your choice. Say .. Downloads or whatever.. So it will look like

Downloads/solr-4.8.1/

On your prompt.. Navigate inside the directory

shankar@shankar-lenovo: cd Downloads/solr-4.8.1

So now you are here..

shankar@shankar-lenovo: ~/Downloads/solr-4.8.1$ 

Start the Jetty Application Server

Jetty is available inside the examples folder of the solr-4.8.1 directory , so navigate inside that and start the Jetty Application Server.

shankar@shankar-lenovo:~/Downloads/solr-4.8.1/example$ java -jar start.jar

Do not close the terminal, minimize it and let it stay aside.

Tip : Use & after start.jar to make the Jetty Server run in the background

To check if Apache Solr runs successfully, visit this URL on the browser.

http://localhost:8983/solr

Running Jetty on custom Port

It runs on the port 8983 as default. You could change the port either here or directly inside the jetty.xml file.

java -Djetty.port=9091 -jar start.jar

Download the JConnector

This JAR file acts as a bridge between MySQL and JDBC , Download the Platform Independent Version here

After downloading it, extract the folder and copy the mysql-connector-java-5.1.31-bin.jar and paste it to the lib directory.

shankar@shankar-lenovo:~/Downloads/solr-4.8.1/contrib/dataimporthandler/lib

Creating the MySQL table to be linked to Apache Solr

To put Solr to use, You need to have some tables and data to search for. For that, we will use MySQL for creating a table and pushing some random names and then we could use Solr to connect to MySQL and index that table and it’s entries.

1. Table Structure

CREATE TABLE test_solr_mysql
     (
      id INT UNSIGNED NOT NULL AUTO_INCREMENT,
      name VARCHAR(45) NULL,
      created TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
      PRIMARY KEY (id)
     );

2. Populate the above table

    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Jean');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Jack');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Jason');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Vego');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Grunt');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Jasper');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Fred');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Jenna');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Rebecca');
    INSERT INTO `test_solr_mysql` (`name`) VALUES ('Roland');

Getting inside the core and adding the lib directives

1. Navigate to

shankar@shankar-lenovo: ~/Downloads/solr-4.8.1/example/solr/collection1/conf

2. Modifying the solrconfig.xml

Add these two directives to this file..

<lib dir="../../../contrib/dataimporthandler/lib/" regex=".*\.jar" />
      <lib dir="../../../dist/" regex="solr-dataimporthandler-\d.*\.jar" />

Now add the DIH (Data Import Handler)

    <requestHandler name="/dataimport" 
      class="org.apache.solr.handler.dataimport.DataImportHandler" >
        <lst name="defaults">
          <str name="config">db-data-config.xml</str>
        </lst>
    </requestHandler>

3. Create the db-data-config.xml file

If the file exists then ignore, add these lines to that file. As you can see the first line, you need to provide the credentials of your MySQL database. The Database name, username and password.

    <dataConfig>
        <dataSource type="JdbcDataSource" driver="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost/yourdbname" user="dbuser" password="dbpass"/>
        <document>
       <entity name="test_solr" query="select CONCAT('test_solr-',id) as rid,name from test_solr_mysql WHERE '${dataimporter.request.clean}' != 'false'
          OR `created` > '${dataimporter.last_index_time}'" >
        <field name="id" column="rid" />
        <field name="solr_name" column="name" />
        </entity>
       </document>
    </dataConfig>

Tip : You can have any number of entities but watch out for id field, if they are same then indexing will skipped.

4. Modify the schema.xml file

Add this to your schema.xml as shown..

<uniqueKey>id</uniqueKey>
<field name="solr_name" type="string" indexed="true" stored="true" />

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Implementation

Indexing

This is where the real deal is. You need to do the indexing of data from MySQL to Solr inorder to make use of Solr Queries.

Step 1: Go to Solr Admin Panel

Hit the URL http://localhost:8983/solr on your browser. The screen opens like this.

As the marker indicates, go to Logging inorder to check if any of the above configuration has led to errors.

Step 2: Check your Logs

Ok so now you are here, As you can see there are a lot of yellow messages (WARNINGS). Make sure you don’t have error messages marked in red. Earlier, on our configuration we had added a select query on our db-data-config.xml, say if there were any errors on that query, it would have shown up here.

Fine, no errors. We are good to go. Let’s choose collection1 from the list as depicted and select Dataimport

Step 3: DIH (Data Import Handler)

Using the DIH, you will be connecting to MySQL from Solr through the configuration file db-data-config.xml from the Solr interface and retrieve the 10 records from the database which gets indexed onto Solr.

To do that, Choose full-import , and check the options Clean and Commit. Now click Execute as shown.

Alternatively, you could use a direct full-import query like this too..

http://localhost:8983/solr/collection1/dataimport?command=full-import&commit=true

After you clicked Execute, Solr begins to index the records, if there were any errors, it would say Indexing Failed and you have to go back to the Logging section to see what has gone wrong.

Assuming there are no errors with this configuration and if the indexing is successfully complete., you would get this notification.

Step 4: Running Solr Queries

Seems like everything went well, now you could use Solr Queries to query the data that was indexed. Click the Query on the left and then press Execute button on the bottom.

You will see the indexed records as shown.

The corresponding Solr query for listing all the records is

http://localhost:8983/solr/collection1/select?q=*:*&wt=json&indent=true

Well, there goes all 10 indexed records. Say, we need only names starting with Ja , in this case, you need to target the column name solr_name, Hence your query goes like this.

http://localhost:8983/solr/collection1/select?q=solr_name:Ja*&wt=json&indent=true

That’s how you write Solr Queries. To read more about it, Check this beautiful article.

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