Scrapy provides various request deduplication mechanisms to avoid crawling the same pages repeatedly. By default, Scrapy uses the RFPDupeFilter class to implement request deduplication, which determines whether requests are duplicates based on request fingerprints. Request fingerprints are unique identifiers generated based on URL, request method, request body, etc. Scrapy also supports custom deduplication filters, and developers can create their own deduplication logic by implementing the DupeFilter interface. For example, Redis can be used to implement distributed deduplication, or specific business rules can be used to determine whether requests are duplicates. Scrapy's deduplication mechanism can also be tuned through configuration files, such as setting the deduplication filter class, setting the size of the deduplication queue, etc. For certain special scenarios, deduplication for specific requests can be disabled through the dont_filter=True parameter. A reasonable deduplication mechanism can avoid repeated crawling, improve spider efficiency, and reduce pressure on target websites.