【发布时间】：2013-06-28 10:16:01
【问题描述】：
使用 Python 和 Sqlalchemy 在 sqlite 数据库中将相同的值作为布尔值或整数存储会产生以下结果。
Value stored as Boolean:
SqlAlchemy ORM: Total time for 40000 records 62.5009999275 secs
SqlAlchemy Core: Total time for 40000 records 56.0600001812 secs
Value stored as Integer:
SqlAlchemy ORM: Total time for 40000 records 5.72099995613 secs
SqlAlchemy Core: Total time for 40000 records 0.770999908447 secs
为什么在使用布尔类型时会出现这样的性能问题？
我知道 SQLite 没有布尔类型的概念，而是将它们存储为整数 1 (True) 或 0 (False)。我会假设 SqlAlchemy 只是将 python bool 映射到 Sqlite 整数。
上面用来生成输出的脚本（修改自this问题）：
import time
import sqlite3
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, create_engine, Boolean
from sqlalchemy.orm import scoped_session, sessionmaker
Base = declarative_base()
DBSession = scoped_session(sessionmaker())
class CustomerInteger(Base):
__tablename__ = "customerInteger"
id = Column(Integer, primary_key=True)
name = Column(String(255))
value = Column(Integer)
class CustomerBoolean(Base):
__tablename__ = "customerBoolean"
id = Column(Integer, primary_key=True)
name = Column(String(255))
value = Column(Boolean)
def init_sqlalchemy(dbname = 'sqlite:///sqlalchemy.db'):
global engine
engine = create_engine(dbname, echo=False)
DBSession.remove()
DBSession.configure(bind=engine, autoflush=False, expire_on_commit=False)
Base.metadata.drop_all(engine)
Base.metadata.create_all(engine)
def test_sqlalchemy_orm(n, table):
init_sqlalchemy()
t0 = time.time()
for i in range(n):
customer = table()
customer.name = 'NAME ' + str(i)
customer.value = True
DBSession.add(customer)
if i % 1000 == 0:
DBSession.flush()
DBSession.commit()
print "SqlAlchemy ORM: Total time for " + str(n) + " records " + str(time.time() - t0) + " secs"
def test_sqlalchemy_core(n, table):
init_sqlalchemy()
t0 = time.time()
engine.execute(
table.__table__.insert(),
[{"name":'NAME ' + str(i), "value":True } for i in range(n)]
)
print "SqlAlchemy Core: Total time for " + str(n) + " records " + str(time.time() - t0) + " secs"
if __name__ == '__main__':
print "Value stored as Boolean:"
test_sqlalchemy_orm(40000, CustomerBoolean)
test_sqlalchemy_core(40000, CustomerBoolean)
print "Value stored as Integer:"
test_sqlalchemy_orm(40000, CustomerInteger)
test_sqlalchemy_core(40000, CustomerInteger)
【问题讨论】：
-
我怀疑是因为 SQLite 本身不支持布尔类型。因此它需要由 ORM 转换为整数，但是我不希望这样的性能损失。
-
只是让你知道：我在我的机器上运行了这个并且没有这个显着的差异。我正在使用 Python
2.7.5和 SQLAlchemy 版本0.8.1运行 ArchLinux。你能发布你的版本吗？
标签： python sqlite sqlalchemy