Riak QL

Introduction

riak_ql provides a number of different functions to Riak

• a lexer/parser for the SQL sub-set we support
• a function for calculating time quanta for Time Series
• a compiler for generating helper modules to validate and manipulate records that correspond to a defined table schema in the DDL

Link to the official and still private docs.

This README is an overview of the repo. Individual sub-systems have their own documentation which will be linked to as appropriate.

Table Of Contents

This document contains the following sections:

• Repository Contents
• Runtime Tools
• SQL Lexer/Parser
• Time Quantiser Fn
• DDL Compiler
• Runtime Query Fns
• Testing Strategy

Repository Contents

This application contains the following files:

• riak_ql_cmd.erl
• riak_ql_ddl_compiler.erl
• riak_ql_ddl.erl
• riak_ql_lexer.xrl
• riak_ql_parser.yrl
• riak_ql_quanta.erl
• riak_ql_to_string.erl
• riak_ql_window_agg_fns.erl

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Runtime Tools

There is an escript that lets you run the lexer/parser from the command line - it is designed to help developers/operators check their syntax.

• riak_ql_cmd.erl

Please read the inline documentation for this module.

SQL Lexer/Parser

The SQL Lexer/Parser takes a string representation of a SQL query and then compiles it. The modules that perform this are:

• riak_ql_lexer.xrl
• riak_ql_parser.yrl

Running ./rebar compile transforms this pair of leex and yecc files into the executable Erlang counterparts:

• riak_ql_lexer.erl
• riak_ql_parser.erl

For more details of the lexer and parser see the Lexer And Parser

To understand how the lexer/parser fits into the query pipeline see Query Pipeline

There is a ruby script and set of SQL keywords which can be used to generate some of the lexer components of riak_lexer.xrl:

• priv/keyword_general.rb
• priv/riak_ql_keywords.csv

For more details see the Lexer Keywords

This code generates one of two output records:

• ddl_v1{} - which captures the CREATE TABLE... statement
• riak_select_v1{} - which captures a SELECT * FROM... statement

NOTE: the output of the lexer is a proplist of record field names and values - the actual record is constructed over the fence from riak_ql in riak_kv for the purposes of simplifying inter-repo dependency management.

Time Quantiser

Time quantisation is done by the module:

• riak_ql_quanta.erl

Please read the inline documentation for this module.

DDL Compiler

The DDL compiler is implemented by:

• riak_ql_ddl_compiler.erl
• riak_ql_ddl.erl

When a CREATE TABLE... statement if fed into the lexer/parser it generates a #ddl_v1{} - a data description language. This captures the structure of the table. The DDL compiler then generates a helper module for that table which allows for the programmatic manipulation of data in that particular format via a common and fixed API.

The module riak_ql_ddl_compiler.erl performs the compilation and the module riak_ql_ddl.erl provides a set of wrappers around the compiled module to add utility functions to the API.

For more details see the DDL Compiler

Runtime Query Fns

The runtime query system performs operations on data in the query pipeline by calling a set of library functions. These are defined in:

• riak_ql_window_agg_fns.erl

Testing Strategy

Details of the testing strategy are written up in riak_test And Test Strategy