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Fast CSV and JSON Ingestion in PostgreSQL with COPY

Jonathan S. Katz
PostgreSQL

If you have been asked to provide a CSV that someone can open up in their favorite spreadsheet editor, chances are you have used the PostgreSQL COPY command. COPY has been around since the early open source releases of PostgreSQL back in the late 1990s and was designed to quickly get data in and out of PostgreSQL.

COPY is also incredibly helpful for ingesting data into a table, especially if you have a lot of it to ingest, and will generally outperform INSERT. Let’s explore a few ways to use COPY to load some data into a table.

 

The Setup

To demonstrate, I will be using PostgreSQL 10.3 loaded from a Docker image.

 We will be creating two different tables, one that will store the results from ingesting data from a CSV and another for the JSON data.

For the CSV data:

CREATE TABLE blog_feed (
    id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
    ingested_at timestamp DEFAULT CURRENT_TIMESTAMP,
    author text NOT NULL,
    content text NOT NULL
);

For the JSON data: 

CREATE TABLE news_feed (
    id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
    ingested_at timestamp DEFAULT CURRENT_TIMESTAMP,
    data jsonb NOT NULL
);

Note: We will be using the JSONB data type for the JSON data. JSONB stores JSON data in a binary format which enables features such as advanced indexing.

Note 2: If you are not using PostgreSQL 10 or later, you can substitute the id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY with id serial PRIMARY KEY.

Ingesting a CSV

In order to demonstrate loading a CSV with COPY, it would help to have data in a CSV to load! Fortunately, this can be solved with a simple Python script to generate some random data. In order to generate the data, we will use the Faker library, which you can install with pip or your favorite Python packaging manager. 

The code below will generate 1,000,000 author/content pairs and output them in a file data.csv:

import csv
import datetime
from faker import Faker

fake = Faker()
MAX_RANGE = 1000000

with open('data.csv', 'w') as csvfile:
    field_names = ['author', 'content']
    writer = csv.DictWriter(csvfile, fieldnames=field_names)
    writer.writeheader()
    for i in range(0, MAX_RANGE):
        writer.writerow({
            'author': fake.name(),
            'content': fake.sentence(nb_words=16, variable_nb_words=True),
        })

You can change how many rows are generated by adjusting the MAX_RANGE variable. Save this file as generator_csv.py and generate the data by running:

python generator_csv.py

Generating the CSV can take a few minutes depending on how fast your system is.

Now the fun part: ingesting the CSV file. The code below will read in the CSV file and put it into the blog_feed table within a database named feeds:

cat data.csv | psql -h localhost -p 5432 feeds -c "COPY blog_feed (author, content) FROM STDIN WITH (FORMAT CSV, HEADER TRUE);"

Substitute feeds with the name of the database you created the blog_feed table in.

What does the above command do? The rows from the data.csv file are piped into a connection which then invokes the COPY command. We pass in options to let the COPY command know that we have passed in a CSV file that contains a header, and to only load the author and content columns from the CSV.

This operation should run relatively quickly: within a matter of seconds you will have all 1,000,000 rows loaded. If you inspect the table, you will see that the data from the CSV made it into the table: 

feeds=# SELECT * FROM blog_feed LIMIT 10 OFFSET 1000;
 id  |     ingested_at         | author |                                                                           content
------+----------------------------+------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------
1001 | 2018-04-02 10:20:10.048562 | Kevin Barron     | Feeling without really here hot popular order think law all main behind hold production significant yes dark blue.
1002 | 2018-04-02 10:20:10.048562 | Rodney Robinson  | Get security seven finally minute she name majority anyone.
1003 | 2018-04-02 10:20:10.048562 | Ryan Jones       | Build professor exist six market soon yes car dream area government test benefit agent return space good style weight.
1004 | 2018-04-02 10:20:10.048562 | Kristin Burke    | Media likely know sound clear score perform buy child section blue save.
1005 | 2018-04-02 10:20:10.048562 | Haley Bowman     | Control become represent west his during until article middle reason agreement television real risk kind form these politics control begin white everything.
1006 | 2018-04-02 10:20:10.048562 | Thomas Young     | Evidence mouth ask picture time issue safe floor phone hot full.
1007 | 2018-04-02 10:20:10.048562 | Edward Bates     | Record system each appear most onto environment until sea likely particularly red seem.
1008 | 2018-04-02 10:20:10.048562 | Angela Reyes     | Partner job beat social point western address especially relate interesting alone.
1009 | 2018-04-02 10:20:10.048562 | Michelle Glenn   | Sound already save glass particular certain idea course cause agent onto improve exist lose physical star little note officer you director someone.
1010 | 2018-04-02 10:20:10.048562 | James Walker Jr. | Physical word course high product best girl blood west continue environmental major hand.

Now you have access to all the wonderful features of PostgreSQL, such as finding out the top 10 authors that appeared in this blog feed:

feeds=# SELECT author,count(*) FROM blog_feed GROUP BY author ORDER BY count DESC LIMIT 10;

     author       | count
-------------------+-------
Michael Smith     | 455
David Smith       | 354
Michael Johnson   | 337
Michael Williams  | 317
James Smith       | 313
John Smith        | 312
Jennifer Smith    | 305
Christopher Smith | 291
Robert Smith      | 284
Michael Jones     | 260

Ingesting JSON Data

Now let’s perform the same exercise but for JSON data. We will be ingesting the JSON data into the “news_feed” table. First, let’s generate some JSON data that can be placed into a file named data.json. The script below is similar to the CSV generation script: tweak the number of JSON objects generated by adjusting the value in MAX_RANGE:

import csv
import datetime
import json
import uuid
from faker import Faker

fake = Faker()
MAX_RANGE = 1000000
datetime_end = datetime.datetime.now()
datetime_start = datetime_end - datetime.timedelta(days=365)

# geneate JSON
with open('data.json', 'w') as f:
    for i in range(0, MAX_RANGE):
        f.write(json.dumps({
            'id': str(uuid.uuid4()),
            'author': fake.name(),
            'content': fake.sentence(nb_words=16, variable_nb_words=True),
            'source': fake.company(),
            'published_at': fake.date_time_between_dates(
                datetime_start=datetime_start,
                datetime_end=datetime_end,
            ).isoformat()
        }) + "\n")

Save this script into a file named generator_json.py.  You can generate the data with the following command:

python generator_json.py

Now let’s ingest the JSON data. The command to ingest this data is similar to that of the CSV, substituting table and column names where appropriate:

cat data.json | psql -h localhost -p 5432 feeds -c "COPY news_feed (data) FROM STDIN;"

Much like the CSV ingestion, the JSON ingestion should run relatively quickly. If you inspect the data, you will find that the JSON data was ingested as expected:

feeds=# SELECT * FROM news_feed LIMIT 2 OFFSET 1000;

 id  |     ingested_at         |                                                                                                                                                                     data    
------+----------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1953 | 2018-04-02 10:44:59.838267 | {"id": "17b70258-d2e6-4ae5-aa29-89e6568899c1", "author": "Civil stock current executive top stand effect near claim tell final east music option officer thing.", "source": "Williams-Pacheco", "content": "Foot tough bad meet third particularly share western expert air detail reality read option wind too while hotel your interest.", "published_at": "2018-02-07T19:19:56"}
1954 | 2018-04-02 10:44:59.838267 | {"id": "5614ab36-3f8d-4382-b92f-3038b6bcce88", "author": "Spring worker book example your others wrong order better lose hard whatever well morning official.", "source": "Summers, Hall and Harrell", "content": "Space something six east happy impact dinner opportunity region.", "published_at": "2017-07-16T01:47:02"}

With the JSON data ingested, we can now use PostgreSQL to analyze the data. For instance, if we wanted to find the top 10 authors in the news feed: 

feeds=# SELECT data->>'author' AS author, count(*)
FROM news_feed
GROUP BY author
ORDER BY count DESC LIMIT 10;


     author       | count
-------------------+-------
Michael Smith     | 475
Michael Johnson   | 390
Jennifer Smith    | 321
John Smith        | 310
Michael Williams  | 308
James Smith       | 302
David Smith       | 299
Christopher Smith | 294
Michael Brown     | 283
Robert Smith      | 278

Bonus: Inspecting JSON Documents

PostgreSQL 9.4 introduced both the JSONB data type as well as the tools to quickly search for data stored within a JSON document via GIN indexes. To create a GIN index on the news_feed column, execute the following command:

CREATE INDEX news_feed_data_gin_idx ON news_feed USING GIN(data);

This enables you to perform several key JSONB operations, such searching for elements inside the document. For example, let’s say I know there is a document with a UUID of 81865b56-4b76-4d33-86fe-660f96861ea0 and I want to pull all of its contents. I can do so quickly with the following query:

SELECT * FROM news_feed WHERE data @> '{ "id": "81865b56-4b76-4d33-86fe-660f96861ea0" }';

There are many other things you can do with JSON objects with PostgreSQL, including interacting with them via procedural languages. Now you have the tools to ingest JSON data quickly and manipulate it!

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