parquet

A library for reading and writing parquet files.

Programming language: Go

License: MIT License

Tags: Files    

Latest version: v0.4.0

README

Parquet

Parquet generates a parquet reader and writer based on a struct. The struct can be defined by you or it can be generated by reading an existing parquet file.

We (Parsyl) will respond to pull requests and issues to the best of our abilities. However, sometimes we will have higher priorities and the response might not be immediate.

NOTE: If you generate the code based on a parquet file there are quite a few limitations. The PageType of each PageHeader must be DATA_PAGE and the Codec (defined in ColumnMetaData) must be PLAIN or SNAPPY. Also, the parquet file's schema must consist of the currently supported types. But wait, there's more! Some of the encodings, like DELTA_BINARY_PACKED, BIT_PACKED, PLAIN_DICTIONARY, and DELTA_BYTE_ARRAY are also not supported. I would guess there are other parquet options that will cause problems since there are so many possibilities.

Installation

go get -u github.com/parsyl/parquet/...

This will also install parquet's only two dependencies: thift and snappy

Usage

First define a struct for the data to be written to parquet:

type Person struct {
    ID  int32  `parquet:"id"`
    Age *int32 `parquet:"age"`
}

Next, add a go:generate comment somewhere (in this example all code lives in main.go):

// go:generate parquetgen -input main.go -type Person -package main

Generate the code for the reader and writer:

$ go generate

A new file (parquet.go) has now been written that defines ParquetWriter and ParquetReader. Next, make use of the writer and reader:

package main

import (
    "bytes"
    "encoding/json"
)

func main() {
    var buf bytes.Buffer
    w, err := NewParquetWriter(&buf)
    if err != nil {
        log.Fatal(err)
    }

    w.Add(Person{ID: 1, Age: getAge(30)})
    w.Add(Person{ID: 2})

    // Each call to write creates a new parquet row group.
    if err := w.Write(); err != nil {
        log.Fatal(err)
    }

    // Close must be called when you are done.  It writes
    // the parquet metadata at the end of the file.
    if err := w.Close(); err != nil {
        log.Fatal(err)
    }

    r, err := NewParquetReader(bytes.NewReader(buf.Bytes()))
    if err != nil {
        log.Fatal(err)
    }

    enc := json.NewEncoder(os.Stdout)
    for r.Next() {
        var p Person
        r.Scan(&p)
        enc.Encode(p)
    }

    if err := r.Error(); err != nil {
        log.Fatal(err)
    }
}

func getAge(a int32) *int32 { return &a }

NewParquetWriter has a couple of optional arguments available: MaxPageSize, Uncompressed, and Snappy. For example, the following sets the page size (number of rows in a page before a new one is created) and sets the page data compression to snappy:

w, err := NewParquetWriter(&buf, MaxPageSize(10000), Snappy)

See [this](./examples/people) for a complete example of how to generate the code based on an existing struct.

See [this](./examples/via_parquet) for a complete example of how to generate the code based on an existing parquet file.

Supported Types

The struct used to define the parquet data can have the following types:

int32
uint32
int64
uint64
float32
float64
string
bool

Each of these types may be a pointer to indicate that the data is optional. The struct can also embed another struct:

type Being struct {
    ID  int32  `parquet:"id"`
    Age *int32 `parquet:"age"`
}

type Person struct {
    Being
    Username string `parquet:"username"`
}

Nested and repeated structs are supported too:

type Being struct {
    ID  int32  `parquet:"id"`
    Age *int32 `parquet:"age"`
}

type Person struct {
    Being    Being
    Username string `parquet:"username"`
    Friends  []Being
}

If you want a field to be excluded from parquet you can tag it with a dash or make it unexported like so:

type Being struct {
    ID  int32  `parquet:"id"`
    Password string`parquet:"-"` //will not be written to parquet
    age int32                    //will not be written to parquet
}

Parquetgen

Parquetgen is the command that go generate should call in order to generate the code for your custom type. It also can print the page headers and file metadata from a parquet file:

$ parquetgen --help
Usage of parquetgen:
  -ignore
        ignore unsupported fields in -type, otherwise log.Fatal is called when an unsupported type is encountered (default true)
  -import string
        import statement of -type if it doesn't live in -package
  -input string
        path to the go file that defines -type
  -metadata
        print the metadata of a parquet file (-parquet) and exit
  -output string
        name of the file that is produced, defaults to parquet.go (default "parquet.go")
  -package string
        package of the generated code
  -pageheaders
        print the page headers of a parquet file (-parquet) and exit (also prints the metadata)
  -parquet string
        path to a parquet file (if you are generating code based on an existing parquet file or printing the file metadata or page headers)
  -struct-output string
        name of the file that is produced, defaults to parquet.go (default "generated_struct.go")
  -type string
        name of the struct that will used for writing and reading