Improved delay handling#57
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EgbertW wants to merge 1 commit intoyasserg:masterfrom
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CrawlController / PageFetcher instance which means that any two requests are at least 200 ms apart. This only makes sense for the same host. The new approach stores the last fetch time for each hostname and maintains a list of recently visited hosts, making sure that at least 200 ms are between requests to the same host while allowing multiple requests within the same ms over different hosts. Now, to optimally utilize this, the distribution of getNextURLs from the frontier should be such that the pages are distributed over the various hosts. This is still a todo. Additionally, a method to return the best URL to visit now, given a selection of URLs, has been added. It checks the delay that would result from each available URL and if any delay is 0 it is returned. If none result in no delay, the one with the lowest delay is returned. Reduces the delay significantly.
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Note: I recently discovered that you moved from google code to Github. I've been using and modifying crawlerj4 for a while now and now I'm able to submit pull requests to allow you to merge them. I rebased all my (relevant) patches on the new master, so they should be easy to merge. I hope you consider some or all of them useful.
Description of this patch:
The original version had a politeness delay per CrawlController / PageFetcher instance which means that any two requests are at least 200 ms apart. This only makes sense for the same host. The new approach stores the last fetch time for each hostname and maintains a list of recently visited hosts, making sure that at least 200 ms are between requests to the same host while allowing multiple requests within the same ms over different hosts. Now, to optimally utilize this, the distribution of getNextURLs from the frontier should be such that the pages are distributed over the various hosts. For this, a method to return the best URL to visit now, given a
selection of URLs, has been added. It checks the delay that would result from each available URL and if any delay is 0 it is returned. If none result in no delay, the one with the lowest delay is returned. Reduces the delay significantly.