Question

我使用scrapy下载大量数据。我使用默认的16个并发请求。如指南所示，我使用管道方法process_item来收集共享变量的数据。并在close_spider将数据保存到SQL。如果我加载太大的网站，我会丢失所有系统内存。我该如何避免这个问题？

现在我使用一个以open_spider方法准备的数据库连接，我无法同时在每个process_item中使用它。

Answer 1

在管道中创建已删除项目的列表，一旦该列表的大小大于N，则调用DB函数以保存数据。这是我项目的100％工作代码。请参阅close_spider()，在蜘蛛关闭时，self.items可能包含少于N个项目，因此self.items列表中的任何剩余数据也将保存在数据库中蜘蛛关闭了。

from scrapy import signals

class YourPipeline(object):

    def __init__(self):
        self.items = []

    def process_item(self, item, spider):

        self.items.extend([ item ])

        if len(self.items) >= 50:
            self.insert_current_items(spider)   
        return item

    def insert_current_items(self, spider):
        for item in self.items:
            update_query = ', '.join(["`" + key + "` = %s " for key, value in item.iteritems()])

            query = "SELECT asin FROM " + spider.tbl_name + " WHERE asin = %s LIMIT 1"

            spider.cursor.execute(query, (item['asin']))

            existing = spider.cursor.fetchone()

            if spider.cursor.rowcount > 0:

                query = "UPDATE " + spider.tbl_name + " SET " + update_query + ", date_update = CURRENT_TIMESTAMP WHERE asin = %s"

                update_query_vals = list(item.values())
                update_query_vals.extend([existing['YOUR_UNIQUE_COLUMN']])


                try:
                    spider.cursor.execute(query, update_query_vals)
                except Exception as e:
                    if 'MySQL server has gone away' in str(e):
                        spider.connectDB()
                        spider.cursor.execute(query, update_query_vals)
                    else:
                        raise e

            else:

                # This ELSE is likely never to get executed because we are not scraping ASINS from Amazon website, we just import ASINs into DB from another script
                try:
                    placeholders = ', '.join(['%s'] * len(item))
                    columns = ', '.join(item.keys())
                    query = "INSERT INTO %s ( %s ) VALUES ( %s )" % (spider.tbl_name, columns, placeholders)
                    spider.cursor.execute(query, item)
                except Exception as e:
                    if 'MySQL server has gone away' in str(e):
                        spider.connectDB()
                        spider.cursor.execute(query, item)
                    else:
                        raise e


        self.items = []



    def close_spider(self, spider):
        self.insert_current_items(spider)

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