使用pyspark连接PostgreSQL

Question

I am trying to connect to a database with pyspark and I am using the following code:

sqlctx = SQLContext(sc)
df = sqlctx.load(
    url = "jdbc:postgresql://[hostname]/[database]",
    dbtable = "(SELECT * FROM talent LIMIT 1000) as blah",
    password = "MichaelJordan",
    user =  "ScottyPippen",
    source = "jdbc",
    driver = "org.postgresql.Driver"
)

and I am getting the following error:

Any idea why is this happening?

Edit : I am trying to run the code locally in my computer.

Answer 1

Download the PostgreSQL JDBC Driver from https://jdbc.postgresql.org/download.html

Then replace the database configuration values by yours.

from pyspark.sql import SparkSession

spark = SparkSession \
    .builder \
    .appName("Python Spark SQL basic example") \
    .config("spark.jars", "/path_to_postgresDriver/postgresql-42.2.5.jar") \
    .getOrCreate()

df = spark.read \
    .format("jdbc") \
    .option("url", "jdbc:postgresql://localhost:5432/databasename") \
    .option("dbtable", "tablename") \
    .option("user", "username") \
    .option("password", "password") \
    .option("driver", "org.postgresql.Driver") \
    .load()

df.printSchema()

More info:https://spark.apache.org/docs/latest/sql-data-sources-jdbc.html

Answer 2

The following worked for me with postgres on localhost:

Download the PostgreSQL JDBC Driver from https://jdbc.postgresql.org/download.html .

For the pyspark shell you use the SPARK_CLASSPATH environment variable:

$ export SPARK_CLASSPATH=/path/to/downloaded/jar
$ pyspark

For submitting a script via spark-submit use the --driver-class-path flag:

$ spark-submit --driver-class-path /path/to/downloaded/jar script.py

In the python script load the tables as a DataFrame as follows:

from pyspark.sql import DataFrameReader

url = 'postgresql://localhost:5432/dbname'
properties = {'user': 'username', 'password': 'password'}
df = DataFrameReader(sqlContext).jdbc(
    url='jdbc:%s' % url, table='tablename', properties=properties
)

or alternatively:

df = sqlContext.read.format('jdbc').\
    options(url='jdbc:%s' % url, dbtable='tablename').\
    load()

Note that when submitting the script via spark-submit , you need to define the sqlContext .

Answer 3

It is necesary copy postgresql-42.1.4.jar in all nodes... for my case, I did copy in the path /opt/spark-2.2.0-bin-hadoop2.7/jars

Also, i set classpath in ~/.bashrc (export SPARK_CLASSPATH="/opt/spark-2.2.0-bin-hadoop2.7/jars" )

and work fine in pyspark console and jupyter

Answer 4

You normally need either:

1. to install the Postgres Driver on your cluster,
2. to provide the Postgres driver jar from your client with the --jars option
3. or to provide the maven coordinates of the Postgres driver with --packages option.

If you detail how are you launching pyspark, we may give you more details.

Some clues/ideas:

spark-cannot-find-the-postgres-jdbc-driver

Not able to connect to postgres using jdbc in pyspark shell

Answer 5

One approach, building on the example per the quick start guide , is this blog post which shows how to add the --packages org.postgresql:postgresql:9.4.1211 argument to the spark-submit command.

This downloads the driver into ~/.ivy2/jars directory, in my case /Users/derekhill/.ivy2/jars/org.postgresql_postgresql-9.4.1211.jar . Passing this as the --driver-class-path option gives the full spark-submit command of:

/usr/local/Cellar/apache-spark/2.0.2/bin/spark-submit\
 --packages org.postgresql:postgresql:9.4.1211\
 --driver-class-path /Users/derekhill/.ivy2/jars/org.postgresql_postgresql-9.4.1211.jar\
 --master local[4] main.py

And in main.py :

from pyspark.sql import SparkSession

spark = SparkSession.builder.getOrCreate()

dataframe = spark.read.format('jdbc').options(
        url = "jdbc:postgresql://localhost/my_db?user=derekhill&password=''",
        database='my_db',
        dbtable='my_table'
    ).load()

dataframe.show()

Answer 6

To use pyspark and jupyter notebook notebook: first open pyspark with

pyspark --driver-class-path /spark_drivers/postgresql-42.2.12.jar  --jars /spark_drivers/postgresql-42.2.12.jar

Then in jupyter notebook

import os
jardrv = "~/spark_drivers/postgresql-42.2.12.jar"


from pyspark.sql import SparkSession
spark = SparkSession.builder.config('spark.driver.extraClassPath', jardrv).getOrCreate()
url = 'jdbc:postgresql://127.0.0.1/dbname'
properties = {'user': 'usr', 'password': 'pswd'}
df = spark.read.jdbc(url=url, table='tablename', properties=properties)

Answer 7

I had trouble to get a connection to the postgresDB with the jars i had on my computer. This code solved my problem with the driver

 from pyspark.sql import SparkSession
 import os

 sparkClassPath = os.environ['PYSPARK_SUBMIT_ARGS'] = '--packages org.postgresql:postgresql:42.1.1 pyspark-shell'

 spark = SparkSession \
    .builder \
    .config("spark.driver.extraClassPath", sparkClassPath) \
    .getOrCreate()

 df = spark.read \
    .format("jdbc") \
    .option("url", "jdbc:postgresql://localhost:5432/yourDBname") \
    .option("driver", "org.postgresql.Driver") \
    .option("dbtable", "yourtablename") \
    .option("user", "postgres") \
    .option("password", "***") \
    .load()

df.show()

Answer 8

This exception means jdbc driver does not in driver classpath. you can spark-submit jdbc jars with --jar parameter, also add it into driver classpath using spark.driver.extraClassPath .

Answer 9

I also get this error

java.sql.SQLException: No suitable driver
 at java.sql.DriverManager.getDriver(Unknown Source)

and add one item .config('spark.driver.extraClassPath', './postgresql-42.2.18.jar') in SparkSession - that worked.

eg:

from pyspark import SparkContext, SparkConf
import os
from pyspark.sql.session import SparkSession

spark = SparkSession \
    .builder \
    .appName('Python Spark Postgresql') \
    .config("spark.jars", "./postgresql-42.2.18.jar") \
    .config('spark.driver.extraClassPath', './postgresql-42.2.18.jar') \
    .getOrCreate()


df = spark.read \
    .format("jdbc") \
    .option("url", "jdbc:postgresql://localhost:5432/abc") \
    .option("dbtable", 'tablename') \
    .option("user", "postgres") \
    .option("password", "1") \
    .load()

df.printSchema()

Answer 10

Just initialize pyspark with --jars <path/to/your/jdbc.jar>

Eg: pyspark --jars /path/Downloads/postgresql-42.2.16.jar

then create a dataframe as suggested above in other answers

Eg:

df2 = spark.read.format("jdbc").option("url", "jdbc:postgresql://localhost:5432/db").option("dbtable", "yourTableHere").option("user", "postgres").option("password", "postgres").option("driver", "org.postgresql.Driver").load()

Answer 11

1. Download postgresql jar from here :
2. Add this to ~Spark/jars/ folder.
3. Restart your kernel. It should work.