Payloads are byte arrays (optionally) stored with every term on a field. Payloads may be used for several use cases in Solr, like boosting certain terms over others. Another use is POS tagging.
Term boosting with Payloads
Imagine the following use cases:
- You index a large HTML page in your body field, but want to boost words in headings and with boldface
- You want to boost all nouns (say you have a clever client side parser which detects nouns)
- Indexing German content, you want to boost all names more than other (capitalized) nouns
You have a product called "Word" and want to boost all occurrences over the lowercase "word" words
All these cases may be solved by introducing payloads in your scoring, given you have the client side magic to detect the words. The beauty is that since the boost is stored with the term, you do not need any heavy parsing or calculation query time. All documents originally containing "Word" would surf up higher in your results, even if everything is lowercased both on index and query side. And even if HTML markup is lost after parsing, your parser would already have tagged the titles and boldface words before removing the markup.
For a step-by-step description on how to enable Payload boosting, see Lucid's blog post here.