Many crawlers face the problem of slow grasping, especially if they need to collect large amounts of data. Improving the crawling efficiency of crawlers is a key issue, and the following will introduce some effective methods to improve the efficiency of crawlers:
1. Minimize the number of website visits
A single crawler mainly consumes time in waiting for a response to a network request, so reducing the number of website visits can effectively reduce the time spent on crawling. Optimizing the crawl process, streamlining the process, and avoiding repetitive retrieval of information on multiple pages can reduce unnecessary visits. Deduplication is another very important means, through the unique identification of url or id, has been crawled pages do not need to continue to climb, so as to avoid repeated requests for the same data.
2. Distributed crawlers
Even with various optimization methods, the number of pages that a single machine can crawl per unit time is still limited. Faced with a large number of pages waiting to be crawled, using distributed crawlers can increase the number of machines to buy more crawling time. The first step of the distributed crawler is to split the task so that multiple machines perform independent and non-repetitive tasks, thereby reducing the workload of each machine and greatly reducing the overall crawl time. For example, if you have 2 million pages to crawl, you can use five machines to crawl 400,000 pages each, which is a five-fold reduction in crawl time compared to a single machine.
In some cases, there is a need to communicate, such as a dynamically changing queue to be crawled, each crawl causes the queue to change, and even splitting the task may lead to cross-duplication, because each machine has a different queue to be crawled while the program is running. In this case, only a distributed crawler can be used, where one Master node is responsible for storing the queue, and multiple other Slave nodes obtain tasks from the queue respectively, so that the shared queue is realized and repeated crawling is avoided.
3. Use the agent IP address and User-Agent properly
When crawling, anti-crawler measures such as IP blocking and User-Agent identification are often encountered. To circumvent these problems, you can use proxy IP to hide the real IP address, as well as replace the User-Agent to simulate different types of browser access. By using high-quality proxy IP and random User-Agent, the probability of being identified as a crawler by the website can be reduced, thus improving the efficiency and success rate of crawling.
4. Asynchronous crawl
Using an asynchronous crawl allows the crawler to wait for certain resources without being blocked, thus increasing efficiency. By sending requests asynchronously, multiple requests can be processed simultaneously, rather than sequentially. This can maximize the use of network resources, improve the crawl speed.
5. Scheduled task and incremental crawl
A scheduled task is a crawl task that is automatically triggered at a predetermined time interval to obtain the data of the target website on a regular basis. By setting a scheduled task, you can avoid frequent manual crawling, save human resources, and ensure timely data update. The scheduled task can be executed at different intervals, such as every day, every hour, or every other time. This can maintain the timeliness of the data, so that the crawler can continuously monitor the changes of the target website and obtain the latest data. Incremental crawling is a strategy that only crawls new or updated data from the target website, rather than re-crawls data that has already been retrieved. This saves time and resources and improves the efficiency of the crawler. Before crawling data, you need to record the timestamp or data version number of the last climb, and then on the next climb, only the data that is newer than the last timestamp or version number. This avoids repeated crawling of all the data for the entire site.
In summary, the methods to improve the crawling efficiency include reducing the number of website visits, using distributed crawlers, rational use of proxy IP and User-Agent, asynchronous crawling, and scheduled tasks and incremental crawling. Through rational use of these methods, the efficiency of the crawler can be greatly improved and the required data can be collected more efficiently.