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FQL

demo gif

FQL provides a query language and an alternative client API for Foundation DB. Some things this project aims to achieve are:

  • Provide a query language for FDB.
  • Provide a textual description of key-value schemas.
  • Provide a Go API which is structurally equivalent to the query language.
  • Simplify the ergonomics of the FoundationDB API.
    • Gracefully handle multi-transaction range-reads.
    • Gracefully handle transient errors.
  • Provide an environment for exploring FDB data.
  • Import/Export subsets of FDB data.

Building & Running

Without Docker

With the Foundation DB client library (>= v6.2.0) and Go (>= v1.20) installed, you can simply run go build in the root of this repo. This will create an fql binary in the root of the repo.

Docker Environment

Building, linting, and testing can all be performed in a Docker environment. This allows any host to perform these operations with only Docker as a dependency. The build.sh script can be used to perform these operations. This is the same script used by the CI/CD workflow of this repo.

To build, lint, & test the current state of the codebase, run ./build.sh --verify. To learn more about the build script, run ./build.sh --help.

Docker Image

FQL is available as a Docker image for executing queries. The first argument passed to the container is the contents of the cluster file. The remaining arguments are passed to the FQL binary.

# 'my_cluster:[email protected]:4500' is used as the contents
# for the cluster file. '-log' and '/my/dir(<>)=42' are passed
# as args to the FQL binary.
docker run docker.io/janderland/fql 'my_cluster:[email protected]:4500' -log '/my/dir(<>)=42'

Within the cluster file contents (first argument), any instances of a hostname wrapped in curly braces (e.g. '{my_hostname}') are replaced by the equivalent IP address. FDB doesn't support connecting to a cluster via hostnames, so this functional provides a workaround. This can simplify connecting to a Docker instance of FDB.

docker network create my_net
docker run --network my_net --name fdb -d foundationdb/foundationdb

# The substring '{fdb}' in the first argument will be replaced with
# the IP address of the FDB container started above before the cluster
# file is written to disk.
docker run --network my_net docker.io/janderland/fql 'docker:docker@{fdb}:4500' -log '/my/dir(<>)=42'

Query Language

Here is the syntax definition for the query language. Currently, FQL is focused on reading & writing key-values created using the directory and tuple layers. Reading or writing keys of arbitrary byte strings is not supported.

FQL queries are a textual representation of a specific key-value or a schema describing the structure of many key-values. These queries have the ability to write a key-value, read one or more key-values, and list directories.

Components & Structure

This section will explain the components and structure of an FQL query. The semantic meaning of these queries will be explained below in the Kinds of Queries section.

Primitives

FQL utilizes textual representations of the element types supported by the tuple layer. These types are known as primitives. Besides as tuple elements, primitives can also be used as the value portion of a key-value.

Type Example
nil nil
int -14
uint 7
bool true
float 33.4
string "string"
bytes 0xa2bff2438312aac032
uuid 5a5ebefd-2193-47e2-8def-f464fc698e31

When primitives are used as tuple elements, they are encoded using the tuple layer. When they are used as the value portion of a key-value, they are encoded by FQL as outlined below.

Type Encoding
nil nil
int 64-bit, endianness configurable
uint 64-bit, endianness configurable
bool single bit, 0 means false
float IEEE 754, endianness configurable
string ASCII byte string
bytes As provided
uuid 16-byte string

Ideally, the encoding of these primitives would align with common community practices to maximize usefulness. Let me know if you believe it doesn't.

Even though a big int encoding is supported by the tuple layer, FQL does not currently support using big ints.

Directories

A directory is specified as a sequence of strings, each prefixed by a forward slash:

/my/dir/path_way

The strings of the directory do not need quotes if they only contain alphanumericals, underscores, dashes, or periods. To use other symbols, the strings must be quoted:

/my/"dir@--\o/"/path_way

The quote character may be backslash escaped:

/my/"\"dir\""/path_way

Tuples

A tuple is specified as a sequence of elements, separated by commas, wrapped in a pair of curly braces. The elements may be a tuple or any of the primitive types.

("one", 2, 0x03, ( "subtuple" ), 5825d3f8-de5b-40c6-ac32-47ea8b98f7b4)

The last element of a tuple may be the ... token.

(0xFF, "thing", ...)

Any combination of spaces, tabs, and newlines is allowed after the opening
brace and commas.

(
  1,
  2,
  3,
)

Key-Values

A key-value is specified as a directory, tuple, equal symbol, and value appended together:

/my/dir("this", 0)=0xabcf03

The value following the equal symbol may be any of the primitives or a tuple:

/my/dir(22.3, -8)=("another", "tuple")

The value can also be the clear token.

/some/where("home", "town", 88.3)=clear

Variables

A variable may be used in place of a directory element, tuple element, or value.

/my/dir/<>("first", <>, "third")=<>

If the variable is a tuple element or value, it may contain a list of primitive types separated by pipes, except for the nil type. The variable may also contain the any type which is equivalent to specifying every type. Specifying no types is also equivalent to specifying the any type.

/my/dir("that", <int|float|bytes>)=<any>

Kinds of Queries

This section showcases the various kinds of FQL queries, their semantic meaning, and the equivalent FDB API calls implemented in Go.

Set

Set queries write a single key-value. The query must not contain the clear or ... tokens, nor a variable.

/my/dir("hello", "world")=42

db.Transact(func(tr fdb.Transaction) (interface{}, error) {
  dir, err := directory.CreateOrOpen(tr, []string{"my", "dir"}, nil)
  if err != nil {
    return nil, err
  }

  val := make([]byte, 8)
  binary.LittleEndian.PutUint64(val, 42)
  tr.Set(dir.Pack(tuple.Tuple{"hello", "world"}), val)
  return nil, nil
})

Clear

Clear queries delete a single key-value. The query must contain the clear token as it's value and must not contain the ... token or variables.

/my/dir("hello", "world")=clear

db.Transact(func(tr fdb.Transaction) (interface{}, error) {
  dir, err := directory.Open(tr, []string{"my", "dir"}, nil)
  if err != nil {
    if errors.Is(err, directory.ErrDirNotExists) {
      return nil, nil
    }
    return nil, err
  }

  tr.Clear(dir.Pack(tuple.Tuple{"hello", "world"}))
  return nil, nil
})

Read Single Key

Read-single queries read a single key-value. These queries must not have the ... token or a variable in their key. The value must be a variable.
Deserialization of the value is attempted for each type in the order specified by the variable. The first successful deserialization is used as the output. If the value cannot be deserialized as any of the types specified then the key-value is not returned or an error is returned, depending on configuration.

/my/dir(99.8, 7dfb10d1-2493-4fb5-928e-889fdc6a7136)=<int|string>

db.Transact(func(tr fdb.Transaction) (interface{}, error) {
  dir, err := directory.Open(tr, []string{"my", "dir"}, nil)
  if err != nil {
    if errors.Is(err, directory.ErrDirNotExists) {
      return nil, nil
    }
    return nil, err
  }

  val := tr.MustGet(dir.Pack(tuple.Tuple{99.8,
    tuple.UUID{0x7d, 0xfb, 0x10, 0xd1, 0x24, 0x93, 0x4f, 0xb5, 0x92, 0x8e, 0x88, 0x9f, 0xdc, 0x6a, 0x71, 0x36}))
  
     
  if len(val) == 8 {
      return binary.LittleEndian.Uint64(val), nil
  }
  return string(val), nil
})

As a shorthand, these query may be specified without the = token or value. This implies an empty variable as the value. In the code block below, the three queries are equivalent.

/my/dir(99.8, 7dfb10d1-2493-4fb5-928e-889fdc6a7136)
/my/dir(99.8, 7dfb10d1-2493-4fb5-928e-889fdc6a7136)=<>
/my/dir(99.8, 7dfb10d1-2493-4fb5-928e-889fdc6a7136)=<any>

Read Range of Keys

Read-many queries read a range of values based on a key prefix. These queries have a ... token or a variable in their key. If a key-value is encountered which does not match the schema defined by the query then the key-value is not returned or an error is returned, depending on configuration. These queries are implemented using FDB's range-read mechanism with additional filtering performed on the client. Care must be taken with these queries as they may result in large amounts of data being sent to the client and most of the data being filtered out.

/people(3392, <string|int>, <>)=(<uint>, ...)

db.ReadTransact(func(tr fdb.ReadTransaction) (interface{}, error) {
  dir, err := directory.Open(tr, []string{"people"}, nil)
  if err != nil {
    if errors.Is(err, directory.ErrDirNotExists) {
      return nil, nil
    }
    return nil, err
  }

  rng, err := fdb.PrefixRange(dir.Pack(tuple.Tuple{3392}))
  if err != nil {
    return nil, err
  }

  var results []fdb.KeyValue
  iter := tr.GetRange(rng, fdb.RangeOptions{}).Iterator()
  for iter.Advance() {
    kv := iter.MustGet()

    tup, err := dir.Unpack(kv.Key)
    if err != nil {
      return nil, err
    }

    if len(tup) != 3 {
      return nil, fmt.Errorf("invalid kv: %v", kv)
    }

    switch tup[0].(type) {
    default:
      return nil, fmt.Errorf("invalid kv: %v", kv)
    case string | int64:
    }

    val, err := tuple.Unpack(kv.Value)
    if err != nil {
      return nil, fmt.Errorf("invalid kv: %v", kv)
    }
    if len(val) == 0 {
      return nil, fmt.Errorf("invalid kv: %v", kv)
    }
    if _, isInt := val[0].(uint64); !isInt {
      return nil, fmt.Errorf("invalid kv: %v", kv)
    }

    results = append(results, kv)
  }
  return results, nil
})

List Directory Paths

If only a directory is provided as a query, then the directory layer is queried. Empty variables may be included as placeholders for any directory name.

/root/<>/items/<>

db.ReadTransact(func(tr fdb.ReadTransaction) (interface{}, error) {
  root, err := directory.Open(tr, []string{"root"}, nil)
  if err != nil {
    if errors.Is(err, directory.ErrDirNotExists) {
      return nil, nil
    }
    return nil, err
  }

  oneDeep, err := root.List(tr, nil)
  if err != nil {
    return nil, err
  }

  var results [][]string
  for _, dir1 := range oneDeep {
    twoDeep, err := root.List(tr, []string{dir1, "items"})
    if err != nil {
      return nil, err
    }

    for _, dir2 := range twoDeep {
      results = append(results, []string{"root", dir1, dir2})
    }
  }
  return results, nil
})