解決Scrapy-Redis爬取完畢以後繼續空跑的問題

時間 2019-11-09

標籤解決 scrapy redis 完畢以後繼續空跑問題欄目 Python 简体版

原文原文鏈接

解決Scrapy-Redis爬取完畢以後繼續空跑的問題

1. 背景

根據scrapy-redis分佈式爬蟲的原理，多臺爬蟲主機共享一個爬取隊列。當爬取隊列中存在request時，爬蟲就會取出request進行爬取，若是爬取隊列中不存在request時，爬蟲就會處於等待狀態，行以下：html

E:\Miniconda\python.exe E:/PyCharmCode/redisClawerSlaver/redisClawerSlaver/spiders/main.py
2017 -12 -12 15: 54: 18 [scrapy.utils.log] INFO: Scrapy 1.4 .0 started (bot: scrapybot)
2017 -12 -12 15: 54: 18 [scrapy.utils.log] INFO: Overridden settings: { 'SPIDER_LOADER_WARN_ONLY': True}
2017 -12 -12 15: 54: 18 [scrapy.middleware] INFO: Enabled extensions:
[ 'scrapy.extensions.corestats.CoreStats',
'scrapy.extensions.telnet.TelnetConsole',
'scrapy.extensions.logstats.LogStats']
2017 -12 -12 15: 54: 18 [myspider_redis] INFO: Reading start URLs from redis key 'myspider:start_urls' (batch size: 110, encoding: utf -8
2017 -12 -12 15: 54: 18 [scrapy.middleware] INFO: Enabled downloader middlewares:
[ 'scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware',
'scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware',
'scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware',
'redisClawerSlaver.middlewares.ProxiesMiddleware',
'redisClawerSlaver.middlewares.HeadersMiddleware',
'scrapy.downloadermiddlewares.retry.RetryMiddleware',
'scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware',
'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware',
'scrapy.downloadermiddlewares.redirect.RedirectMiddleware',
'scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware',
'scrapy.downloadermiddlewares.stats.DownloaderStats']
2017 -12 -12 15: 54: 18 [scrapy.middleware] INFO: Enabled spider middlewares:
[ 'scrapy.spidermiddlewares.httperror.HttpErrorMiddleware',
'scrapy.spidermiddlewares.offsite.OffsiteMiddleware',
'scrapy.spidermiddlewares.referer.RefererMiddleware',
'scrapy.spidermiddlewares.urllength.UrlLengthMiddleware',
'scrapy.spidermiddlewares.depth.DepthMiddleware']
2017 -12 -12 15: 54: 18 [scrapy.middleware] INFO: Enabled item pipelines:
[ 'redisClawerSlaver.pipelines.ExamplePipeline',
'scrapy_redis.pipelines.RedisPipeline']
2017 -12 -12 15: 54: 18 [scrapy.core.engine] INFO: Spider opened
2017 -12 -12 15: 54: 18 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2017 -12 -12 15: 55: 18 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2017 -12 -12 15: 56: 18 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)

但是，若是全部的request都已經爬取完畢了呢？這件事爬蟲程序是不知道的，它沒法區分結束和空窗期狀態的不一樣，因此會一直處於上面的那種等待狀態，也就是咱們說的空跑。
那有沒有辦法讓爬蟲區分這種狀況，自動結束呢？

2. 環境

系統：win7
scrapy-redis
redis 3.0.5
python 3.6.1

3. 解決方案

從背景介紹來看，基於scrapy-redis分佈式爬蟲的原理，爬蟲結束是一個很模糊的概念，在爬蟲爬取過程當中，爬取隊列是一個不斷動態變化的過程，隨着request的爬取，又會有新的request進入爬取隊列。進進出出。爬取速度高於填充速度，就會有隊列空窗期（爬取隊列中，某一段時間會出現沒有request的狀況），爬取速度低於填充速度，就不會出現空窗期。因此對於爬蟲結束這件事來講，只能模糊定義，沒有一個精確的標準。
因此，下面這兩種方案都是一種大概的思路。

3.1. 利用scrapy的關閉spider擴展功能

參考官方文檔：http://scrapy-chs.readthedocs.io/zh_CN/0.24/topics/extensions.html

# 關閉spider擴展
class scrapy.contrib.closespider.CloseSpider
當某些情況發生，spider會自動關閉。每種狀況使用指定的關閉緣由。
關閉spider的狀況能夠經過下面的設置項配置：
CLOSESPIDER_TIMEOUT
CLOSESPIDER_ITEMCOUNT
CLOSESPIDER_PAGECOUNT
CLOSESPIDER_ERRORCOUNT

CLOSESPIDER_TIMEOUT

CLOSESPIDER_TIMEOUT
默認值: 0
一個整數值，單位爲秒。若是一個spider在指定的秒數後仍在運行，它將以 closespider_timeout 的緣由被自動關閉。若是值設置爲 0（或者沒有設置），spiders不會由於超時而關閉。

CLOSESPIDER_ITEMCOUNT

CLOSESPIDER_ITEMCOUNT
缺省值: 0
一個整數值，指定條目的個數。若是spider爬取條目數超過了指定的數，而且這些條目經過item pipeline傳遞，spider將會以 closespider_itemcount 的緣由被自動關閉。

CLOSESPIDER_PAGECOUNT

CLOSESPIDER_PAGECOUNT
0 .11 新版功能.
缺省值: 0
一個整數值，指定最大的抓取響應( reponses)數。若是 spider抓取數超過指定的值，則會以 closespider_pagecount 的緣由自動關閉。若是設置爲0（或者未設置）， spiders不會由於抓取的響應數而關閉。

CLOSESPIDER_ERRORCOUNT

CLOSESPIDER_ERRORCOUNT
0 .11 新版功能.
缺省值: 0
一個整數值，指定 spider能夠接受的最大錯誤數。若是 spider生成多於該數目的錯誤，它將以 closespider_errorcount 的緣由關閉。若是設置爲0（或者未設置）， spiders不會由於發生錯誤過多而關閉。

示例：打開 settings.py，添加一個配置項，以下

# 爬蟲運行超過23.5小時，若是爬蟲尚未結束，則自動關閉
CLOSESPIDER_TIMEOUT = 84600

特別注意：若是爬蟲在規定時限沒有把request所有爬取完畢，此時強行中止的話，爬取隊列中就還會存有部分request請求。那麼爬蟲下次開始爬取時，必定要記得在master端對爬取隊列進行清空操做。

3.2. 修改scrapy-redis源碼

# ----------- 修改scrapy-redis源碼時，特別須要注意的是：---------
# 第一，要留有原始代碼的備份。
# 第二，當項目移植到其餘機器上時，須要將scrapy-redis源碼一塊兒移植過去。通常代碼位置在\Lib\site-packages\scrapy_redis\下

想象一下，爬蟲已經結束的特徵是什麼？那就是爬取隊列已空，從爬取隊列中沒法取到request信息。那着手點應該就在從爬取隊列中獲取request和調度這個部分。查看scrapy-redis源碼，咱們發現了兩個着手點：

3.2.1. 細節python

# .\Lib\site-packages\scrapy_redis\schedluer.py
def next_request(self):
block_pop_timeout = self.idle_before_close
# 下面是從爬取隊列中彈出request
# 這個block_pop_timeout 我還沒有研究清除其做用。不過確定不是超時時間......
request = self.queue.pop(block_pop_timeout)
if request and self. stats:
self.stats.inc_value( 'scheduler/dequeued/redis', spider= self.spider)
return request

# .\Lib\site-packages\scrapy_redis\spiders.py
def next_requests(self):
"" "Returns a request to be scheduled or none." ""
use_set = self.settings.getbool( 'REDIS_START_URLS_AS_SET', defaults.START_URLS_AS_SET)
fetch_one = self.server.spop if use_set else self.server.lpop
# XXX: Do we need to use a timeout here?
found = 0
# TODO: Use redis pipeline execution.
while found < self. redis_batch_size:
data = fetch_one( self.redis_key)
if not data:
# 表明爬取隊列爲空。可是多是永久爲空，也多是暫時爲空
# Queue empty.
break
req = self.make_request_from_data(data)
if req:
yield req
found += 1
else:
self.logger.debug( "Request not made from data: %r", data)
if found:
self.logger.debug( "Read %s requests from '%s'", found, self.redis_key)

參考註釋，從上述源碼來看，就只有這兩處能夠作手腳。可是爬蟲在爬取過程當中，隊列隨時均可能出現暫時的空窗期。想判斷爬取隊列爲空，通常是設定一個時限，若是在一個時段內，隊列一直持續爲空，那咱們能夠基本認定這個爬蟲已經結束了。因此有了以下的改動：

# .\Lib\site-packages\scrapy_redis\schedluer.py
# 原始代碼
def next_request(self):
block_pop_timeout = self.idle_before_close
request = self.queue.pop(block_pop_timeout)
if request and self. stats:
self.stats.inc_value( 'scheduler/dequeued/redis', spider= self.spider)
return request
# 修改後的代碼
def __init__(self, server,
persist=False,
flush_on_start=False,
queue_key=defaults.SCHEDULER_QUEUE_KEY,
queue_cls=defaults.SCHEDULER_QUEUE_CLASS,
dupefilter_key=defaults.SCHEDULER_DUPEFILTER_KEY,
dupefilter_cls=defaults.SCHEDULER_DUPEFILTER_CLASS,
idle_before_close=0,
serializer=None):
# ......
# 增長一個計數項
self.lostGetRequest = 0
def next_request(self):
block_pop_timeout = self.idle_before_close
request = self.queue.pop(block_pop_timeout)
if request and self. stats:
# 若是拿到了就恢復這個值
self.lostGetRequest = 0
self.stats.inc_value( 'scheduler/dequeued/redis', spider= self.spider)
if request is None:
self.lostGetRequest += 1
print(f "request is None, lostGetRequest = {self.lostGetRequest}, time = {datetime.datetime.now()}")
# 100個大概8分鐘的樣子
if self.lostGetRequest > 200:
print(f "request is None, close spider.")
# 結束爬蟲
self.spider.crawler.engine.close_spider( self.spider, 'queue is empty')
return request

相關log信息

2017 -12 -14 16: 18: 06 [scrapy.middleware] INFO: Enabled item pipelines:
[ 'redisClawerSlaver.pipelines.beforeRedisPipeline',
'redisClawerSlaver.pipelines.amazonRedisPipeline',
'scrapy_redis.pipelines.RedisPipeline']
2017 -12 -14 16: 18: 06 [scrapy.core.engine] INFO: Spider opened
2017 -12 -14 16: 18: 06 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
request is None, lostGetRequest = 1, time = 2017 -12 -14 16: 18: 06.370400
request is None, lostGetRequest = 2, time = 2017 -12 -14 16: 18: 11.363400
request is None, lostGetRequest = 3, time = 2017 -12 -14 16: 18: 16.363400
request is None, lostGetRequest = 4, time = 2017 -12 -14 16: 18: 21.362400
request is None, lostGetRequest = 5, time = 2017 -12 -14 16: 18: 26.363400
request is None, lostGetRequest = 6, time = 2017 -12 -14 16: 18: 31.362400
request is None, lostGetRequest = 7, time = 2017 -12 -14 16: 18: 36.363400
request is None, lostGetRequest = 8, time = 2017 -12 -14 16: 18: 41.362400
request is None, lostGetRequest = 9, time = 2017 -12 -14 16: 18: 46.363400
request is None, lostGetRequest = 10, time = 2017 -12 -14 16: 18: 51.362400
2017 -12 -14 16: 18: 56 [scrapy.core.engine] INFO: Closing spider (queue is empty)
request is None, lostGetRequest = 11, time = 2017 -12 -14 16: 18: 56.363400
request is None, close spider.
登陸結果：loginRes = ( 235, b 'Authentication successful')
登陸成功，code = 235
mail has been send successfully. message:Content-Type: text/plain; charset= "utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: base64
From: 548516910@qq.com
To: 548516910@qq.com
Subject: =?utf -8?b? 54is6Jmr57uT5p2f54q25oCB5rGH5oql77yabmFtZSA9IHJlZGlzQ2xhd2VyU2xhdmVyLCByZWFzb24gPSBxdWV1ZSBpcyBlbXB0eSwgZmluaXNoZWRUaW1lID0gMjAxNy0xMi0xNCAxNjoxODo1Ni4zNjQ0MDA=?=
57uG6IqC77yacmVhc29uID0gcXVldWUgaXMgZW1wdHksIHN1Y2Nlc3NzISBhdDoyMDE3LTEyLTE0
IDE2OjE4OjU2LjM2NDQwMA==
2017 -12 -14 16: 18: 56 [scrapy.statscollectors] INFO: Dumping Scrapy stats:
{ 'finish_reason': 'queue is empty',
'finish_time': datetime.datetime(2017, 12, 14, 8, 18, 56, 364400),
'log_count/INFO': 8,
'start_time': datetime.datetime(2017, 12, 14, 8, 18, 6, 362400)}
2017 -12 -14 16: 18: 56 [scrapy.core.engine] INFO: Spider closed (queue is empty)
Unhandled Error
Traceback (most recent call last):
File "E:\Miniconda\lib\site-packages\scrapy\commands\runspider.py", line 89, in run
self.crawler_process.start()
File "E:\Miniconda\lib\site-packages\scrapy\crawler.py", line 285, in start
reactor.run(installSignalHandlers= False) # blocking call
File "E:\Miniconda\lib\site-packages\twisted\internet\base.py", line 1243, in run
self.mainLoop()
File "E:\Miniconda\lib\site-packages\twisted\internet\base.py", line 1252, in mainLoop
self.runUntilCurrent()
--- <exception caught here> ---
File "E:\Miniconda\lib\site-packages\twisted\internet\base.py", line 878, in runUntilCurrent
call.func(* call.args, ** call.kw)
File "E:\Miniconda\lib\site-packages\scrapy\utils\reactor.py", line 41, in __call__
return self._func(*self._a, **self._kw)
File "E:\Miniconda\lib\site-packages\scrapy\core\engine.py", line 137, in _next_request
if self.spider_is_idle(spider) and slot.close_if_idle:
File "E:\Miniconda\lib\site-packages\scrapy\core\engine.py", line 189, in spider_is_idle
if self.slot.start_requests is not None:
builtins.AttributeError: 'NoneType' object has no attribute 'start_requests'
2017 -12 -14 16: 18: 56 [twisted] CRITICAL: Unhandled Error
Traceback (most recent call last):
File "E:\Miniconda\lib\site-packages\scrapy\commands\runspider.py", line 89, in run
self.crawler_process.start()
File "E:\Miniconda\lib\site-packages\scrapy\crawler.py", line 285, in start
reactor.run(installSignalHandlers= False) # blocking call
File "E:\Miniconda\lib\site-packages\twisted\internet\base.py", line 1243, in run
self.mainLoop()
File "E:\Miniconda\lib\site-packages\twisted\internet\base.py", line 1252, in mainLoop
self.runUntilCurrent()
--- <exception caught here> ---
File "E:\Miniconda\lib\site-packages\twisted\internet\base.py", line 878, in runUntilCurrent
call.func(* call.args, ** call.kw)
File "E:\Miniconda\lib\site-packages\scrapy\utils\reactor.py", line 41, in __call__
return self._func(*self._a, **self._kw)
File "E:\Miniconda\lib\site-packages\scrapy\core\engine.py", line 137, in _next_request
if self.spider_is_idle(spider) and slot.close_if_idle:
File "E:\Miniconda\lib\site-packages\scrapy\core\engine.py", line 189, in spider_is_idle
if self.slot.start_requests is not None:
builtins.AttributeError: 'NoneType' object has no attribute 'start_requests'
Process finished with exit code 0

有一個問題，如上所述，當經過engine.close_spider(spider, ‘reason’)來關閉spider時，有時會出現幾個錯誤以後才能關閉。多是由於scrapy會開啓多個線程同時抓取，而後其中一個線程關閉了spider，其餘線程就找不到spider纔會報錯。

3.2.2. 注意事項react

整個調度過程以下：redis

scheduler.py
scrapy
queue.py
分佈式
因此，PriorityQueue和另外兩種隊列FifoQueue，LifoQueue有所不一樣，特別須要注意。若是會使用到timeout這個參數，那麼在setting中就只能指定爬取隊列爲FifoQueue或LifoQueue。

# 指定排序爬取地址時使用的隊列，
# 默認的按優先級排序(Scrapy默認)，由sorted set實現的一種非FIFO、LIFO方式。
# 'SCHEDULER_QUEUE_CLASS': 'scrapy_redis.queue.SpiderPriorityQueue',
# 可選的按先進先出排序（FIFO）
'SCHEDULER_QUEUE_CLASS': 'scrapy_redis.queue.SpiderQueue',
# 可選的按後進先出排序（LIFO）
# SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.SpiderStack'

https://blog.csdn.net/mr_hui_/article/details/81455387