#------------------------------------------------------------------------------
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#
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#------------------------------------------------------------------------------
# query_arraysize.py
#
# Demonstrates how to alter the array size and prefetch rows values in order to
# tune the performance of fetching data from the database.  Increasing these
# values can reduce the number of network round trips and overhead required to
# fetch all of the rows from a large table. The value affect internal buffers
# and do not affect how, or when, rows are returned to your application.
#
# The best values need to be determined by tuning in your production
# environment.
#------------------------------------------------------------------------------

import time

import oracledb
import sample_env

# determine whether to use python-oracledb thin mode or thick mode
if not sample_env.get_is_thin():
    oracledb.init_oracle_client(lib_dir=sample_env.get_oracle_client())

connection = oracledb.connect(user=sample_env.get_main_user(),
                              password=sample_env.get_main_password(),
                              dsn=sample_env.get_connect_string())

# Global values can be set to override the defaults used when a cursor is
# created
oracledb.defaults.prefetchrows = 200  # default is 2
oracledb.defaults.arraysize = 200     # default is 100

with connection.cursor() as cursor:

    # Example 1

    start = time.time()

    cursor.execute('select * from bigtab')
    res = cursor.fetchall()

    elapsed = (time.time() - start)
    print("Prefetchrows:", cursor.prefetchrows, "Arraysize:", cursor.arraysize)
    print("Retrieved", len(res), "rows in", elapsed, "seconds")

    # Example 2

    start = time.time()

    # values can be set per-cursor
    cursor.prefetchrows = 1000
    cursor.arraysize = 1000

    cursor.execute('select * from bigtab')
    res = cursor.fetchall()
    # print(res)  # uncomment to display the query results

    elapsed = (time.time() - start)
    print("Prefetchrows:", cursor.prefetchrows, "Arraysize:", cursor.arraysize)
    print("Retrieved", len(res), "rows in", elapsed, "seconds")