为什么MySQL InnoDB插入这么慢？

Question

我正在使用较大的随机数作为密钥（来自另一个系统）。在相当小的表（如几百万行）上进行插入和更新所花费的时间比我认为合理的长得多。

我已经提炼了一个非常简单的测试来说明。在测试表中，我尝试使其尽可能简单。我的真实代码没有如此简单的布局，并具有关系和附加索引等。但是，更简单的设置将显示等效的性能。

结果如下：

creating the MyISAM table took 0.000 seconds
creating 1024000 rows of test data took 1.243 seconds
inserting the test data took 6.335 seconds
selecting 1023742 rows of test data took 1.435 seconds
fetching 1023742 batches of test data took 0.037 seconds
dropping the table took 0.089 seconds
creating the InnoDB table took 0.276 seconds
creating 1024000 rows of test data took 1.165 seconds
inserting the test data took 3433.268 seconds
selecting 1023748 rows of test data took 4.220 seconds
fetching 1023748 batches of test data took 0.037 seconds
dropping the table took 0.288 seconds

在MyISAM中插入1M行需要6秒钟；进入InnoDB需要 3433秒 ！

我究竟做错了什么？什么是配置错误？（MySQL是具有默认值的普通Ubuntu安装）

这是测试代码：

import sys, time, random
import MySQLdb as db

# usage: python script db_username db_password database_name

db = db.connect(host="127.0.0.1",port=3306,user=sys.argv[1],passwd=sys.argv[2],db=sys.argv[3]).cursor()

def test(engine):

    start = time.time() # fine for this purpose
    db.execute("""
CREATE TEMPORARY TABLE Testing123 (
k INTEGER PRIMARY KEY NOT NULL,
v VARCHAR(255) NOT NULL
) ENGINE=%s;"""%engine)
    duration = time.time()-start
    print "creating the %s table took %0.3f seconds"%(engine,duration)

    start = time.time()
    # 1 million rows in 100 chunks of 10K
    data = [[(str(random.getrandbits(48)) if a&1 else int(random.getrandbits(31))) for a in xrange(10*1024*2)] for b in xrange(100)]
    duration = time.time()-start
    print "creating %d rows of test data took %0.3f seconds"%(sum(len(rows)/2 for rows in data),duration)

    sql = "REPLACE INTO Testing123 (k,v) VALUES %s;"%("(%s,%s),"*(10*1024))[:-1]
    start = time.time()
    for rows in data:
        db.execute(sql,rows)
    duration = time.time()-start
    print "inserting the test data took %0.3f seconds"%duration

    # execute the query
    start = time.time()
    query = db.execute("SELECT k,v FROM Testing123;")
    duration = time.time()-start
    print "selecting %d rows of test data took %0.3f seconds"%(query,duration)

    # get the rows in chunks of 10K
    rows = 0
    start = time.time()
    while query:
        batch = min(query,10*1024)
        query -= batch
        rows += len(db.fetchmany(batch))
    duration = time.time()-start
    print "fetching %d batches of test data took %0.3f seconds"%(rows,duration)

    # drop the table
    start = time.time()
    db.execute("DROP TABLE Testing123;")
    duration = time.time()-start
    print "dropping the table took %0.3f seconds"%duration


test("MyISAM")
test("InnoDB")

Answer 1

InnoDB不能很好地应对“随机”主键。尝试顺序键或自动递增，相信您会看到更好的性能。您的“真实”键字段仍可以建立索引，但是对于批量插入，最好在插入完成后一击就删除并重新创建该索引。有兴趣查看您的基准测试！

一些相关问题

• 使用随机PRIMARY KEY列的值将INSERT缓慢插入InnoDB表
• 当有几个索引时，为什么在大型表上进行MySQL InnoDB插入/更新会变得非常慢？
• InnoDB插入速度非常慢并且变慢