Tuesday, February 10, 2015

Autocommit with ceODBC is slow

You already know that in Python it is faster to call executemany() than repeatedly calling execute() to INSERT the same number of rows because executemany() avoids rebinding the parameters, but what about the effect of autocommit on performance? While this is probably not specific to ceODBC, using autocommit is astonishingly slow. Here is how slow.

First, the Python code to run the benchmark:

import ceODBC
import datetime
import os
import time

connection_string="driver=sql server;database=database;server=server;" 
print connection_string

conn = None
cursor = None
def init_db():
    import ceODBC
    global conn
    global cursor
    conn = ceODBC.connect(connection_string)
    cursor = conn.cursor()

def table_exists():
    cursor.execute("select count(1) from information_schema.tables where table_name='zzz_ceodbc_test'")
    return cursor.fetchone()[0] == 1

def create_table():
    print('create_table')
    create_sql="""
CREATE TABLE zzz_ceodbc_test (
    col1 INT,
    col2 VARCHAR(50)
) """
    try:
        cursor.execute(create_sql)
        assert(table_exists())
    except:
        import traceback
        traceback.print_exc()

rows = []
for i in xrange(0,10000):
    rows.append((i,'abcd'))

def log_speed(start_time, end_time, records):
    elapsed_seconds = end_time - start_time
    if elapsed_seconds > 0:
        records_second = int(records / elapsed_seconds)
        # make elapsed_seconds an integer to shorten the string format
        elapsed_str = str(
            datetime.timedelta(seconds=int(elapsed_seconds)))
        print("{:,} records; {} records/sec; {} elapsed".format(records, records_second, elapsed_str))
    else:
        print("counter: %i records " % records)

 
 
def benchmark(bulk, autocommit):
    init_db()
    global conn
    global cursor
    conn.autocommit=True
    cursor.execute('truncate table zzz_ceodbc_test')
    
    conn.autocommit = autocommit
    insert_sql = 'insert into zzz_ceodbc_test (col1, col2) values (?,?)'
    
    start_time = time.time()
    if bulk:
        cursor.executemany(insert_sql, rows)
    else:
        for row in rows:
            cursor.execute(insert_sql, row)
    conn.commit()
    end_time = time.time()
    
    cursor.execute("select count(1) from zzz_ceodbc_test")
    assert cursor.fetchone()[0] == len(rows)
    
    log_speed(start_time, end_time, len(rows))
    conn.autocommit=True
    
    del cursor
    del conn
    return end_time - start_time


def benchmark_repeat(bulk, autocommit, repeats=5):
    description = "%s, autocommit=%s" % ('bulk' if bulk else 'one at a time', autocommit)
    print '\n******* %s' % description
    results = []
    for x in xrange(0, repeats):
        results.append(benchmark(bulk, autocommit))
    print results

benchmark_repeat(True, False)
benchmark_repeat(True, True)
benchmark_repeat(False, True)

And to graph the results in R:

results_table <- 'group seconds
bulk_manual 0.6710000038146973
bulk_manual 0.6710000038146973
bulk_manual 0.9830000400543213
bulk_manual 0.7330000400543213
bulk_manual 0.6710000038146973
bulk_auto 8.486999988555908
bulk_auto 8.269000053405762
bulk_auto 8.980999946594238
bulk_auto 8.453999996185303
bulk_auto 8.480999946594238
one_at_a_time 24.391000032424927
one_at_a_time 23.70300006866455
one_at_a_time 71.66299986839294
one_at_a_time 23.58899998664856
one_at_a_time 37.18400001525879'

results <- read.table(textConnection(results_table), header = TRUE)
closeAllConnections() 

library(ggplot2)
ggplot(results, aes(group, seconds)) + geom_boxplot()

Conclusion: executemany() with autocommit is 76% faster than execute(), and executemany() without autocommit is 91% faster than executemany() with autocommit. Also, executemany() gives more consistent performance.

Ran on Windows 7 Pro 64-bit, Python 2.7.9 32-bit, ceODBC 2.0.1, Microsoft SQL Server 11.0 SP1, R 3.1.2.

2 comments:

  1. This isn't an example of "bulk loading" as understood by most RDBMSs, but rather the result of transaction scoping. The example does single row inserts within one transaction.

    Each RDBMS has its own syntax for loading data from various forms of external flatfiles. (There is also "standard" SQL to copy rows from one table to another.) This method is (in my experience) always the fastest method. Depending on the RDBMS, one may lose (by choice or requirement) transaction semantics, of course.

    ReplyDelete
    Replies
    1. Robert, yes, you are right. I updated the article that executemany() binds the query parameter once, and this is different than bulk loading.

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