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SIT (Streaming Index Toy)

SIT is a lightweight TCP server that provides real-time full-text search over streams of JSON documents. It's also usable as a C library, where it can parse any stream using custom parsers.


  • Lightweight The executable is 228K on my machine. It only depends on libev and libc; and currently (and temporarily) uses Ruby for the build and test suites.
  • True realtime This is "true" real time, as opposed to "near" real time. SIT eliminates garbage collection, "commits," "flushes," and fsyncs. This is search highly optimized for recency and real-time. (However, we have not gone as far as hardware realtime or kernel guarantees)
  • Write, then read Trivially support search results which include the document you just added.
  • Computationally efficient percolation SIT is designed to add documents and execute query callbacks efficiently with up to 100,000 registered queries and/or connections.
  • Flexible pubsub Rather than publishing into channels, you can use SIT to publish into a global event stream, and subscribe to dynamic channels defined by search queries.


SIT speaks a simple line-based pipelineable protocol. Any line that starts with a curly brace ({) is interpreted as a JSON document to add to the indexed dataset. Other lines are interpreted as commands.

All responses are JSON lines, and have a status key, which can be either ok, or error. Other keys are implemented on a per-command basis.

Search & Percolation

SIT provides traditional search, where you give a query and get a resultset back. It also provides percolation, where you can register a query that will notify you when matching documents are added to the index.


  • register QUERY
    Registers the query, or queries, for percolation. When any document that matches the query is added, SIT will print a "found" response in this stream.

    Sample request/response:

      > register title ~ "hello world" AND points > 4;
      < {"status": "ok", "message": "registered", "id": 29}
      # ...
      < {"status": "ok", "message": "found", "query_id": 29, "doc_id": 500, "doc": {"title": "hello sweet world", "points": 7}}

    The response to a register command includes an ID of the registered query.

  • unregister QUERYID
    Give the id provided in the register response, to stop the percolation.

    Sample request/response:

      > unregister 29
      < {"status": "ok", "message": "unregistered", "id": 29}
  • query QUERY
    Do a search.

    Sample request/response:

      # adding some docs
      > {"hello":"world 0"}
      > {"hello":"world 1"}
      > {"hello":"world 2"}
      > {"hello":"world 3"}
      > {"hello":"world 4"}
      > {"hello":"world 5"}
      > {"hello":"world 6"}
      > {"hello":"world 7"}
      > {"hello":"world 8"}
      > {"hello":"world 9"}
      > query hello ~ world LIMIT 5;
      < {"status": "ok", "message": "querying", "id": 27}
      < {"status": "ok", "message": "found", "query_id": 27, "doc_id": 9, "doc": {"hello":"world 9"}}
      < {"status": "ok", "message": "found", "query_id": 27, "doc_id": 8, "doc": {"hello":"world 8"}}
      < {"status": "ok", "message": "found", "query_id": 27, "doc_id": 7, "doc": {"hello":"world 7"}}
      < {"status": "ok", "message": "found", "query_id": 27, "doc_id": 6, "doc": {"hello":"world 6"}}
      < {"status": "ok", "message": "found", "query_id": 27, "doc_id": 5, "doc": {"hello":"world 5"}}
      < {"status": "ok", "message": "complete", "id": 27}

Query Language

SIT has a simple query language, composed of boolean operations (AND, OR, NOT) over clauses. You can append LIMIT N to the end of a query. Queries are terminated with either a newline or a semicolon. The following are valid clauses:

  field_name ~ string 
  field_name > integer
  field_name = integer
  field_name < integer
  field_name >= integer
  field_name <= integer
  field_name != integer


SIT is designed to use pluggable tokenization strategies.

TODO: Describe tokenization 101 basics, concepts, examples.

Supported tokenization strategies

  • whitespace
  • Unicode UAX#29 word boundaries
  • regular expression pattern tokenizer

Pull requests are welcome.

What is the tilde?

The tilde indicates a full-text search. A full-text search identifies documents where a given term is present in the specified field.

The full-text search, title ~ hello will match JSON documents with a field named title which contain a token of hello. For example, the document {"title":"hello full text search"} when tokenized with a simple whitespace tokenizer.

A quoted value for the tilde operator will match documents where all the terms of the quoted text are present in the named field. For example, title ~ "hello world" will be transformed into (title ~ hello AND title ~ world).


  • Nested JSON support
  • Composable streams
  • Persistance
  • Replace
  • wchar/unicode support
  • Facets
  • Aggregations
  • Quoted/span/proximity queries
  • selectable parsers besides JSON in the server? (e.g., log output, msgpack, BSON)

Quick Start

Feeling adventurous? Run SIT on your own system and try some of these demos.

Downloading and building SIT

git clone git://
cd sit
bundle install
bundle exec rake

Demo: Running SIT with simple inputs and searches

Start the server with ./sit, which reads commands from standard input, and prints its output to standard out.

# {"status": "ok", "message": "added", "doc_id": 0"}
query hello ~ world;
# {"status": "ok", "message": "querying", "id": 0}
# {"status": "ok", "message": "found", "query_id": 0, "doc_id": 0, "doc":
# {"hello":"world"}}
# {"status": "ok", "message": "complete", "id": 0}

Demo: Twitter Streaming API

Reminder, this is pre-release software. We use Twitter Streaming APIs as testing to find new and novel edge cases which cause crashes.

You should assume that this demo has a 50/50 chance to format your hard drive, and proceed accordingly (you're piping raw internet data through a pre-release C program).

First, install and authenticate twurl.

Next, start a server listening to the network.

./sit --port 4000
[INFO] [2013:03:0221:15:53] Successfully started server.

Now stream documents from Twitter, via netcat, to your running server.

twurl -t -H /1/statuses/sample.json | nc localhost 4000
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