Forgot to mention that I'm running SQLAlchemy 0.9.4 on 64-bit Python 3.4.0
on Windows.
On Monday, May 12, 2014 3:48:44 PM UTC-4, Seth P wrote:
>
> After tracking down some extreme slowness in loading a one-to-many
> relationship (e.g. myobject.foobars), I seem to have isolated the issue to
> engine.execute() being much slower with parameterized queries than with
> explicit queries. The following is actual code and output for loading
> 10,971 rows from a database table. (The actual table has more columns than
> I'm including here, and is not designed by me.) Note that each explicit
> query (where I explicitly set the WHERE clause parameter and pass the
> resulting SQL statement to engine.execute()) runs in under 0.1 seconds,
> whereas each parameterized query (where I let SQLAlchemy bind the WHERE
> clause parameter) takes over 8 seconds.
>
> The difference in runtimes is smaller when the number of rows returned is
> smaller, which seems odd since I would have thought that the binding of the
> WHERE clause parameters is just done once and would be virtually
> instantaneous.
>
> Any thoughts?
>
> Thanks,
>
> Seth
>
>
> import sqlalchemy as sa
> from sqlalchemy.orm import sessionmaker
> from sqlalchemy.ext.declarative import declarative_base
> import time
>
> engine = sa.create_engine('mssql+pyodbc://Compustat/Compustat')
> session = sessionmaker(bind=engine, autoflush=False,
> expire_on_commit=False)()
>
> class FooBar(declarative_base()):
> __tablename__ = 'sec_dprc'
> gvkey = sa.Column(sa.String(6), primary_key=True)
> datadate = sa.Column(sa.DateTime, primary_key=True)
> value = sa.Column(sa.Float, name='prcod')
>
> def print_timing(func):
> def wrapper(*arg):
> t1 = time.time()
> rows = func(*arg)
> t2 = time.time()
> print("%30s() len=%d, last=%s, runtime=%0.3fs" %
> (str(func).split(' at')[0][10:], len(rows), rows[-1], t2 - t1))
> return t2 - t1
> return wrapper
>
> if __name__ == '__main__':
>
> key = '001045'
> query = session.query(FooBar.datadate,
> FooBar.value).filter(sa.and_(FooBar.gvkey == key)).order_by(FooBar.datadate)
> sql_select_statement_base = str(query)
> print(sql_select_statement_base)
>
> @print_timing
> def execute_explicit_query():
> sql_select_statement_explicit =
> sql_select_statement_base.replace(":gvkey_1", "'%s'" % key)
> rows =
> engine.execute(sa.text(sql_select_statement_explicit)).fetchall()
> return rows
>
> @print_timing
> def execute_parameterized_query():
> rows = engine.execute(sa.text(sql_select_statement_base),
> {'gvkey_1':key}).fetchall()
> return rows
>
> num_iterations = 5
> explicit_runtime = 0.0
> parameterized_runtime = 0.0
> for i in range(num_iterations):
> explicit_runtime += execute_explicit_query()
> parameterized_runtime += execute_parameterized_query()
> print("Total runtime for %d explicit queries = %0.3fs." %
> (num_iterations, explicit_runtime))
> print("Total runtime for %d parameterized queries = %0.3fs." %
> (num_iterations, parameterized_runtime))
>
>
> SELECT sec_dprc.datadate AS sec_dprc_datadate, sec_dprc.prcod AS
> sec_dprc_prcod
> FROM sec_dprc
> WHERE sec_dprc.gvkey = :gvkey_1 ORDER BY sec_dprc.datadate
> execute_explicit_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=0.082s
> execute_parameterized_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=8.852s
> execute_explicit_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=0.032s
> execute_parameterized_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=8.754s
> execute_explicit_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=0.039s
> execute_parameterized_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=9.182s
> execute_explicit_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=0.028s
> execute_parameterized_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=9.416s
> execute_explicit_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=0.080s
> execute_parameterized_query() len=10971, last=(datetime.datetime(2014,
> 5, 9, 0, 0), 37.96), runtime=8.425s
> Total runtime for 5 explicit queries = 0.260s.
> Total runtime for 5 parameterized queries = 44.629s.
>
>
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