多进程对 MySQL update的影响

今天要做数据清洗的时候，要更新一个数据库字段，考虑到用多进程去更新数据库，也许程序会跑得快一些，结果开了64个进程，

结果是其他程序更新的时候，速度非常慢，最后发现的原因是，数据库中有64个SQL语句执行更新，这样就导致了对数据库进行增删改查的速度很慢。

这是一个血的教训，所有以后的操作尽量少用多进程更新数据库。即使是想用多进程进行SQL update，可以少开几个进程，提升效果比较明显

粘贴查来代码，以供以后学习参考

#-*-coding:utf-8-*-

from common.contest import *
import time

def spider(item):

    print "正在清晰地url是：", item['item_url']

    item_url = item['item_url']
    item_lotnum1 = item['item_lotnum']
    item_sold = item['item_sold']
    artron_session_url = item['artron_session_url']
    artfoxlive_session_url = item['artfoxlive_session_url']
    print item_lotnum1
    print item_sold

    try:
        item_lotnum2 = "@@@" + item_lotnum1 + "@@@"
        item_lotnum = re.findall('@@@000(.*?)@@@',item_lotnum2)[0]
    except:
        try:
            item_lotnum2 = "@@@" + item_lotnum1 + "@@@"
            item_lotnum = re.findall('@@@00(.*?)@@@', item_lotnum2)[0]
        except:
            try:
                item_lotnum2 = "@@@" + item_lotnum1 + "@@@"
                item_lotnum = re.findall('@@@0(.*?)@@@', item_lotnum2)[0]
            except:
                item_lotnum = item_lotnum1

    item_sold_cur_spider = ""
    if '流拍' in item_sold:
        item_sold = -2
        item_sold_cur_spider = -2
    elif '撤拍' in item_sold:
        item_sold = -3
        item_sold_cur_spider = -3

    elif '落槌价' in item_sold:
        item_sold1 = str(item_sold).replace('落槌价', '').replace(':', '').replace(',', '').replace('：', '').replace('  ', '').replace('  ', '')
        item_sold = re.findall('\d+', item_sold1)[0]
        item_sold_cur_spider = re.findall('[^\d]+', item_sold1)[0]

    else:
        pass

    print item_sold
    print item_sold_cur_spider
    print artron_session_url
    print artfoxlive_session_url

    item_lotnum = item_lotnum.replace('@','')
    print item_lotnum

    sql = 'update  spider_yachang_2017_2_update_sold_price set item_sold_price_spider2 = %s, item_sold_cur_spider2 = %s 
　　　　　　where session_url=%s and item_lotnum= %s '
    data = (str(item_sold), str(item_sold_cur_spider), str(artron_session_url), str(item_lotnum))
    update_data1(sql, data=data)

if __name__ == "__main__":
    time1 = time.time()
    sql = """
SELECT
    *
FROM
    oversea_artfoxlive_2017_2_detail_info
 """

    resultList = select_data(sql)
    print len(resultList)
    pool = multiprocessing.Pool(64)
    for item in resultList:
        # print "正在爬取的位置是：",resultList.index(item)
        # spider(item)
        pool.apply_async(spider, (item,))
    pool.close()
    pool.join()