dmlogv/vertica-python

Native Python client for the Vertica (www.vertica.com) database.

vertica-python

vertica-python is a native Python adapter for the Vertica (http://www.vertica.com) database.

📢 08/14/2018: vertica-python becomes Vertica’s first officially supported open source database client, see the blog here.

Please check out release notes to learn about the latest improvements.

vertica-python is currently in beta stage; it has been tested for functionality and has a very basic test suite. Please use with caution, and feel free to submit issues and/or pull requests (Read up on our contributing guidelines).

vertica-python has been tested with Vertica 9.1.1 and Python 2.7/3.4/3.5/3.6/3.7.

Installation

If you're using pip >= 1.4 and you don't already have pytz installed:

pip install --pre pytz

If you're using pip >= 1.4 and you don't already have python-dateutil installed:

pip install --pre python-dateutil

To install vertica-python with pip:

pip install vertica-python

Source code for vertica-python can be found at:

https://github.com/vertica/vertica-python

Usage

Create connection

import vertica_python

conn_info = {'host': '127.0.0.1',
             'port': 5433,
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             # autogenerated session label by default,
             'session_label': 'some_label',
             # default throw error on invalid UTF-8 results
             'unicode_error': 'strict',
             # SSL is disabled by default
             'ssl': False,
             # using server-side prepared statements is disabled by default
             'use_prepared_statements': False,
             # connection timeout is not enabled by default
             # 5 seconds timeout for a socket operation (Establishing a TCP connection or read/write operation)
             'connection_timeout': 5}

# simple connection, with manual close
connection = vertica_python.connect(**conn_info)
# do things
connection.close()

# using with for auto connection closing after usage
with vertica_python.connect(**conn_info) as connection:
    # do things

You can pass an ssl.SSLContext to ssl to customize the SSL connection options. For example,

import vertica_python
import ssl

ssl_context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
ssl_context.verify_mode = ssl.CERT_REQUIRED
ssl_context.check_hostname = True
ssl_context.load_verify_locations(cafile='/path/to/ca_file.pem')

conn_info = {'host': '127.0.0.1',
             'port': 5433,
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             'ssl': ssl_context}
connection = vertica_python.connect(**conn_info)

See more on SSL options here.

Logging is disabled by default if you do not pass values to both log_level and log_path. The default value of log_level is logging.WARNING. You can find all levels here. The default value of log_path is 'vertica_python.log', the log file will be in the current execution directory. For example,

import vertica_python
import logging

## Example 1: write DEBUG level logs to './vertica_python.log'
conn_info = {'host': '127.0.0.1',
             'port': 5433,
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             'log_level': logging.DEBUG}
with vertica_python.connect(**conn_info) as connection:
    # do things

## Example 2: write WARNING level logs to './path/to/logs/client.log'
conn_info = {'host': '127.0.0.1',
             'port': 5433,
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             'log_path': 'path/to/logs/client.log'}
with vertica_python.connect(**conn_info) as connection:
   # do things

## Example 3: write INFO level logs to '/home/admin/logs/vClient.log'
conn_info = {'host': '127.0.0.1',
             'port': 5433,
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             'log_level': logging.INFO,
             'log_path': '/home/admin/logs/vClient.log'}
with vertica_python.connect(**conn_info) as connection:
   # do things

Connection Failover: Supply a list of backup hosts to backup_server_node for the client to try if the primary host you specify in the connection parameters (host, port) is unreachable. Each item in the list should be either a host string (using default port 5433) or a (host, port) tuple. A host can be a host name or an IP address.

import vertica_python

conn_info = {'host': 'unreachable.server.com',
             'port': 888,
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             'backup_server_node': ['123.456.789.123', 'invalid.com', ('10.20.82.77', 6000)]}
connection = vertica_python.connect(**conn_info)

Connection Load Balancing helps automatically spread the overhead caused by client connections across the cluster by having hosts redirect client connections to other hosts. Both the server and the client need to enable load balancing for it to function. If the server disables connection load balancing, the load balancing request from client will be ignored.

import vertica_python

conn_info = {'host': '127.0.0.1',
             'port': 5433,
             'user': 'some_user',
             'password': 'some_password',
             'database': 'vdb',
             'connection_load_balance': True}

# Server enables load balancing
with vertica_python.connect(**conn_info) as conn:
    cur = conn.cursor()
    cur.execute("SELECT NODE_NAME FROM V_MONITOR.CURRENT_SESSION")
    print("Client connects to primary node:", cur.fetchone()[0])
    cur.execute("SELECT SET_LOAD_BALANCE_POLICY('ROUNDROBIN')")

with vertica_python.connect(**conn_info) as conn:
    cur = conn.cursor()
    cur.execute("SELECT NODE_NAME FROM V_MONITOR.CURRENT_SESSION")
    print("Client redirects to node:", cur.fetchone()[0])

## Output
#  Client connects to primary node: v_vdb_node0003
#  Client redirects to node: v_vdb_node0005

Another way to set connection properties is passing a connection string to the keyword parameter dsn of vertica_python.connect(dsn='...', **kwargs). The connection string is of the form:

vertica://(user):(password)@(host):(port)/(database)?(arg1=val1&arg2=val2&...)

The connection string would be parsed by vertica_python.parse_dsn(connection_str), and the parsing result (a dictionary of keywords and values) would be merged with kwargs. If the same keyword is specified in both the sources, the kwargs value overrides the parsed dsn value. The (arg1=val1&arg2=val2&...) section can handle string/numeric/boolean values, blank and invalid value would be ignored.

import vertica_python

connection_str = ('vertica://admin@localhost:5433/db1?connection_load_balance=True&connection_timeout=1.5&'
                  'session_label=vpclient+123%7E456')
print(vertica_python.parse_dsn(connection_str))
# {'user': 'admin', 'host': 'localhost', 'port': 5433, 'database': 'db1',
#  'connection_load_balance': True, 'connection_timeout': 1.5, 'session_label': 'vpclient 123~456'}

additional_info = {
    'password': 'some_password', 
    'backup_server_node': ['10.6.7.123', ('10.20.82.77', 6000)]  # invalid value to be set in a connection string
    }

with vertica_python.connect(dsn=connection_str, **additional_info) as conn:
   # do things

Stream query results:

cur = connection.cursor()
cur.execute("SELECT * FROM a_table LIMIT 2")

for row in cur.iterate():
    print(row)
# [ 1, 'some text', datetime.datetime(2014, 5, 18, 6, 47, 1, 928014) ]
# [ 2, 'something else', None ]

Streaming is recommended if you want to further process each row, save the results in a non-list/dict format (e.g. Pandas DataFrame), or save the results in a file.

In-memory results as list:

cur = connection.cursor()
cur.execute("SELECT * FROM a_table LIMIT 2")
cur.fetchall()
# [ [1, 'something'], [2, 'something_else'] ]

In-memory results as dictionary:

cur = connection.cursor('dict')
cur.execute("SELECT * FROM a_table LIMIT 2")
cur.fetchall()
# [ {'id': 1, 'value': 'something'}, {'id': 2, 'value': 'something_else'} ]
connection.close()

Query using named parameters:

cur = connection.cursor()
cur.execute("SELECT * FROM a_table WHERE a = :propA b = :propB", {'propA': 1, 'propB': 'stringValue'})

cur.fetchall()
# [ [1, 'something'], [2, 'something_else'] ]

Query using server-side prepared statements:

Vertica server-side prepared statements let you define a statement once and then run it many times with different parameters. Placeholders in the statement are represented by question marks (?). Server-side prepared statements are useful for preventing SQL injection attacks.

import vertica_python

# Enable using server-side prepared statements at connection level
conn_info = {'host': '127.0.0.1',
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             'use_prepared_statements': True,
             }

with vertica_python.connect(**conn_info) as connection:
    cur = connection.cursor()
    cur.execute("CREATE TABLE tbl (a INT, b VARCHAR)")
    cur.execute("INSERT INTO tbl VALUES (?, ?)", [1, 'aa'])
    cur.execute("INSERT INTO tbl VALUES (?, ?)", [2, 'bb'])
    cur.executemany("INSERT INTO tbl VALUES (?, ?)", [(3, 'foo'), (4, 'xx'), (5, 'bar')])
    cur.execute("COMMIT")

    cur.execute("SELECT * FROM tbl WHERE a>=? AND a<=? ORDER BY a", (2,4))
    cur.fetchall()
    # [[2, 'bb'], [3, 'foo'], [4, 'xx']]

Vertica does not support executing a command string containing multiple statements using server-side prepared statements. You can set use_prepared_statements option in cursor.execute*() functions to override the connection level setting.

import vertica_python

# Enable using server-side prepared statements at connection level
conn_info = {'host': '127.0.0.1',
             'user': 'some_user',
             'password': 'some_password',
             'database': 'a_database',
             'use_prepared_statements': True,
             }

with vertica_python.connect(**conn_info) as connection:
    cur = connection.cursor()
    cur.execute("CREATE TABLE tbl (a INT, b VARCHAR)")

    # Executing compound statements
    cur.execute("INSERT INTO tbl VALUES (?, ?); COMMIT", [1, 'aa'])
    # Error message: Cannot insert multiple commands into a prepared statement

    # Disable prepared statements but forget to change placeholders (?)
    cur.execute("INSERT INTO tbl VALUES (?, ?); COMMIT;", [1, 'aa'], use_prepared_statements=False)
    # TypeError: not all arguments converted during string formatting

    cur.execute("INSERT INTO tbl VALUES (%s, %s); COMMIT;", [1, 'aa'], use_prepared_statements=False)
    cur.execute("INSERT INTO tbl VALUES (:a, :b); COMMIT;", {'a': 2, 'b': 'bb'}, use_prepared_statements=False)

# Disable using server-side prepared statements at connection level
conn_info['use_prepared_statements'] = False
with vertica_python.connect(**conn_info) as connection:
    cur = connection.cursor()

    # Try using prepared statements
    cur.execute("INSERT INTO tbl VALUES (?, ?)", [3, 'foo'])
    # TypeError: not all arguments converted during string formatting

    cur.execute("INSERT INTO tbl VALUES (?, ?)", [3, 'foo'], use_prepared_statements=True)

    # Query using named parameters
    cur.execute("SELECT * FROM tbl WHERE a>=:n1 AND a<=:n2 ORDER BY a", {'n1': 2, 'n2': 4})
    cur.fetchall()
    # [[2, 'bb'], [3, 'foo']]

Note: In other drivers, the batch insert is converted into a COPY statement by using prepared statements. vertica-python currently does not support that.

Insert and commits :

cur = connection.cursor()

# inline commit (when 'use_prepared_statements' is False)
cur.execute("INSERT INTO a_table (a, b) VALUES (1, 'aa'); commit;")

# commit in execution
cur.execute("INSERT INTO a_table (a, b) VALUES (1, 'aa')")
cur.execute("INSERT INTO a_table (a, b) VALUES (2, 'bb')")
cur.execute("commit;")

# connection.commit()
cur.execute("INSERT INTO a_table (a, b) VALUES (1, 'aa')")
connection.commit()

Copy :

cur = connection.cursor()
cur.copy("COPY test_copy (id, name) from stdin DELIMITER ',' ",  csv)

Where csv is either a string or a file-like object (specifically, any object with a read() method). If using a file, the data is streamed.

Rowcount oddities

vertica_python behaves a bit differently than dbapi when returning rowcounts.

After a select execution, the rowcount will be -1, indicating that the row count is unknown. The rowcount value will be updated as data is streamed.

cur.execute('SELECT 10 things')

cur.rowcount == -1  # indicates unknown rowcount

cur.fetchone()
cur.rowcount == 1
cur.fetchone()
cur.rowcount == 2
cur.fetchall()
cur.rowcount == 10

After an insert/update/delete, the rowcount will be returned as a single element row:

cur.execute("DELETE 3 things")

cur.rowcount == -1  # indicates unknown rowcount
cur.fetchone()[0] == 3

Nextset

If you execute multiple statements in a single call to execute(), you can use cursor.nextset() to retrieve all of the data.

cur.execute('SELECT 1; SELECT 2;')

cur.fetchone()
# [1]
cur.fetchone()
# None

cur.nextset()
# True

cur.fetchone()
# [2]
cur.fetchone()
# None

cur.nextset()
# None

UTF-8 encoding issues

While Vertica expects varchars stored to be UTF-8 encoded, sometimes invalid strings get into the database. You can specify how to handle reading these characters using the unicode_error connection option. This uses the same values as the unicode type (https://docs.python.org/2/library/functions.html#unicode)

cur = vertica_python.Connection({..., 'unicode_error': 'strict'}).cursor()
cur.execute(r"SELECT E'\xC2'")
cur.fetchone()
# caught 'utf8' codec can't decode byte 0xc2 in position 0: unexpected end of data

cur = vertica_python.Connection({..., 'unicode_error': 'replace'}).cursor()
cur.execute(r"SELECT E'\xC2'")
cur.fetchone()
# �

cur = vertica_python.Connection({..., 'unicode_error': 'ignore'}).cursor()
cur.execute(r"SELECT E'\xC2'")
cur.fetchone()
# 

License

Apache 2.0 License, please see LICENSE for details.

Contributing guidelines

Have a bug or an idea? Please see CONTRIBUTING.md for details.

Acknowledgements

We would like to thank the contributors to the Ruby Vertica gem (https://github.com/sprsquish/vertica), as this project gave us inspiration and help in understanding Vertica's wire protocol. These contributors are:

• Matt Bauer
• Jeff Smick
• Willem van Bergen
• Camilo Lopez