An Introduction to Sphinx
What is Sphinx?
Sphinx is a search engine. You feed it documents, each with a unique identifier and a bunch of text, and then you can send it search terms, and it will tell you the most relevant documents that match them. If you’re familiar with Lucene, Ferret, Solr or ElasticSearch, it’s pretty similar to those systems. You get the daemon running, your data indexed, and then using a client of some sort, start searching.
If you use SQL-backed indices, Sphinx will talk directly to your data source itself – which when using Thinking Sphinx, must be either MySQL or PostgreSQL – which means it can be very fast to index (if your SQL statements aren’t too complex, anyway).
The alternative is to use real-time indices, which allow for immediate updates to single Sphinx documents (instead of updating a batch at once, which is the only option for SQL-backed indices).
Sphinx Structure
A Sphinx daemon (the process known as searchd) can talk to a collection of indexes. Each index tracks a set of documents, and each document is made up of fields and attributes. While in other areas of software you could use those two terms interchangeably, they have distinctly different meanings in Sphinx.
Fields
Fields are the content for your search queries – so if you want words tied to a specific document, you better make sure they’re in a field in your index. They are only string data – you could have numbers and dates and such in your fields, but Sphinx will only treat them as strings, nothing else.
Attributes
Attributes are used for sorting, filtering and grouping your search results. Their values do not get paid any attention by Sphinx for search terms, though, and they’re limited to the following data types: integers, floats, datetimes (as Unix timestamps – and thus integers anyway), booleans, and strings. Take note that string attributes cannot be used in filters, but only for sorting and grouping.
Multi-Value Attributes
There is also support in Sphinx to handle arrays of attributes for a single document – which go by the name of multi-value attributes. Currently, only integers, big integers (64 bit) and timestamps are supported, so this isn’t quite as flexible as normal attributes, but it’s worth keeping in mind.