How to implement MySQL Buffer Logic in a Scrapy Web Crawler
In web crawlers, buffer logic refers to the set of rules or algorithms used to manage and manipulate the URLs that are being crawled. These rules determine how URLs are added to, removed from, and processed within the buffer.
One example of buffer logic in web crawlers is using a queue data structure as a buffer to store the URLs to be crawled. The URLs are added to the end of the queue and are removed from the front of the queue, following a First-In-First-Out (FIFO) buffer logic. This ensures that the URLs are crawled in the order they were discovered.
Another perspective on buffer logic, it is like a cache you calculate a unique hash (UUID, ULID, SHA1) of the data and save it in the DB. If the hash exists in the DB you skip the duplicate entry (cause the write query cost is more expensive rather than the read), else proceed to transform the data.
Remember from a system design perspective you should choose your hash creation algorithm wisely. Learn more about it here.
Here’s an example of how you might implement buffer logic using MySQL in a Scrapy spider:
import mysql.connector
class MySpider(scrapy.Spider):
name = "myspider"
start_urls = [ ... ]
def __init__(self, *args, **kwargs):
super(MySpider, self).__init__(*args, **kwargs)
self.conn = mysql.connector.connect(
host="hostname",
user="username",
password="password",
database="database"
)
self.cursor = self.conn.cursor()
def parse(self, response):
item = MyItem()
# Extract item data here
# Check if the item's data already exists in the database
self.cursor.execute("SELECT COUNT(*) FROM mytable WHERE column = %s", (item['column'],))
if self.cursor.fetchone()[0] > 0:
# Data already exists, skip this item
return
else:
# Data does not exist, process the item
# ...
# Add item to the database
self.cursor.execute("INSERT INTO mytable (column) VALUES (%s)", (item['column'],))
self.conn.commit()
yield item
def closed(self, reason):
self.cursor.close()
self.conn.close()You need to connect to the mysql database using mysql.connector.connect(...) method, and slight change in the way of passing the values in the query by %s instead of ?. Make sure that you have mysql-connector-python library installed in your environment.
This is just a simple example, you can adjust it to your specific needs. You might want to add error handling and other functionalities. Also, It’s a best practice to use a connection pool in production to maintain many concurrent connections to the database and also prevents opening and closing too many connections.
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