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#------------------------------------------------------------------------------

# session_callback_plsql.py

# Demonstrate how to use a connection pool session callback written in

# PL/SQL. The callback is invoked whenever the tag requested by the application

# does not match the tag associated with the session in the pool. It should be

# used to set session state, so that the application can count on known session

# state, which allows the application to reduce the number of round trips to the

# database.

# The primary advantage to this approach over the equivalent approach shown in

# session_callback.py is when DRCP is used, as the callback is invoked on the

# server and no round trip is required to set state.

# This script requires cx_Oracle 7.1 or higher.

# Also see session_callback.py

#------------------------------------------------------------------------------

import cx_Oracle as oracledb

import sample_env

# create pool with session callback defined

pool = oracledb.SessionPool(user=sample_env.get_main_user(),

password=sample_env.get_main_password(),

dsn=sample_env.get_connect_string(), min=2, max=5,

increment=1,

session_callback="pkg_SessionCallback.TheCallback")

# truncate table logging calls to PL/SQL session callback

with pool.acquire() as conn:

cursor = conn.cursor()

cursor.execute("truncate table PLSQLSessionCallbacks")

# acquire session without specifying a tag; the callback will not be invoked as

# a result and no session state will be changed

print("(1) acquire session without tag")

with pool.acquire() as conn:

cursor = conn.cursor()

cursor.execute("select to_char(current_date) from dual")

result, = cursor.fetchone()

print("main(): result is", repr(result))

# acquire session, specifying a tag; since the session returned has no tag,

# the callback will be invoked; session state will be changed and the tag will

# be saved when the connection is closed

print("(2) acquire session with tag")

with pool.acquire(tag="NLS_DATE_FORMAT=SIMPLE") as conn:

cursor = conn.cursor()

cursor.execute("select to_char(current_date) from dual")

result, = cursor.fetchone()

print("main(): result is", repr(result))

# acquire session, specifying the same tag; since a session exists in the pool

# with this tag, it will be returned and the callback will not be invoked but

# the connection will still have the session state defined previously

print("(3) acquire session with same tag")

with pool.acquire(tag="NLS_DATE_FORMAT=SIMPLE") as conn:

cursor = conn.cursor()

cursor.execute("select to_char(current_date) from dual")

result, = cursor.fetchone()

print("main(): result is", repr(result))

# acquire session, specifying a different tag; since no session exists in the

# pool with this tag, a new session will be returned and the callback will be

# invoked; session state will be changed and the tag will be saved when the

# connection is closed

print("(4) acquire session with different tag")

with pool.acquire(tag="NLS_DATE_FORMAT=FULL;TIME_ZONE=UTC") as conn:

cursor = conn.cursor()

cursor.execute("select to_char(current_date) from dual")

result, = cursor.fetchone()

print("main(): result is", repr(result))

# acquire session, specifying a different tag but also specifying that a

# session with any tag can be acquired from the pool; a session with one of the

# previously set tags will be returned and the callback will be invoked;

# session state will be changed and the tag will be saved when the connection

# is closed

print("(4) acquire session with different tag but match any also specified")

with pool.acquire(tag="NLS_DATE_FORMAT=FULL;TIME_ZONE=MST", matchanytag=True) \

as conn:

cursor = conn.cursor()

cursor.execute("select to_char(current_date) from dual")

result, = cursor.fetchone()

print("main(): result is", repr(result))

# acquire session and display results from PL/SQL session logs

with pool.acquire() as conn:

cursor = conn.cursor()

cursor.execute("""

select RequestedTag, ActualTag

from PLSQLSessionCallbacks

order by FixupTimestamp""")

print("(5) PL/SQL session callbacks")

for requestedTag, actualTag in cursor:

print("Requested:", requestedTag, "Actual:", actualTag)

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