Document reuse in a search engine crawler

1. A method, comprising:

at a computing system having one or more processors and memory storing one or more programs executed by the one or more processors:

retrieving a plurality of records corresponding to prior scheduled crawls of respective documents in a plurality of documents; and

performing a document crawling operation on the plurality of documents, wherein the document crawling operation includes downloading a current version of a respective document from a host computer based on a determination that a document importance score for the respective document exceeds a first threshold, wherein the document importance score is based on a query-independent metric of an importance of the document for a search engine, or reusing a previously downloaded version of a respective document in the plurality of documents instead of downloading a current version of the respective document from a host computer based on a determination that the document importance score does not exceed a first threshold.

2. The method of claim 1 , wherein the plurality of records for a respective document include:

a first record including a first document identifier and a first crawl time for the respective document, and

a second record including a second document identifier and a second crawl time for the respective document,

wherein the first document identifier and the second document identifier correspond to the respective document, and

wherein performing the document crawling operation on the plurality of documents further includes, when the document importance score does not exceed the first threshold:

reusing a previously downloaded version of a respective document in the plurality of documents instead of downloading a current version of the respective document from a host computer when a difference between the first crawl time and a second crawl time does not exceed a second threshold, or

downloading a current version of the respective document from the host computer when a difference between the first crawl time and a second crawl time exceeds the second threshold.

3. The method of claim 1 , further comprising:

retrieving, from a first database, at least a subset of contents of a first document in the plurality of documents, the first document corresponding to a document identifier in a first scheduler record, the first scheduler record including a reuse flag for the first document set to a first state; and

retrieving, from a second database, at least a subset of contents of a second document in the plurality of documents, the second document corresponding to a document identifier in a second scheduler record, the second scheduler record including a reuse flag for the second document set to a second state;

wherein the first and second databases are not the same and wherein the second database stores content from previously crawled documents, including the second document.

4. The method of claim 3 , wherein the first database includes a set of servers and the set of servers is interconnected by a network.

5. The method of claim 3 , wherein the first database includes the World Wide Web.

6. The method of claim 3 , wherein the first database includes a subset of the World Wide Web.

7. The method of claim 3 , further comprising adding the at least a subset of the contents of the first document to the second database.

8. The method of claim 1 , wherein the document importance score associated with the document is based, at least in part, on a number of other documents that reference the document.

9. A computer system comprising:

one or more processors;

memory storing data and one or more programs executed by the one or more processors, the stored data and the one or more programs comprising instructions for:

retrieving a plurality of records corresponding to prior scheduled crawls of respective documents in a plurality of documents; and

performing a document crawling operation on the plurality of documents, wherein the document crawling operation includes downloading a current version of a respective document from a host computer based on a determination that a document importance score for the respective document exceeds a first threshold, wherein the document importance score is based on a query-independent metric of an importance of the document for a search engine, or reusing a previously downloaded version of a respective document in the plurality of documents instead of downloading a current version of the respective document from a host computer based on a determination that the document importance score does not exceed a first threshold.

10. The computer system of claim 9 , wherein the plurality of records for a respective document include:

a first record including a first document identifier and a first crawl time for the respective document, and

a second record including a second document identifier and a second crawl time for the respective document,

wherein the first document identifier and the second document identifier correspond to the respective document, and

wherein performing the document crawling operation on the plurality of documents further includes, when the document importance score does not exceed the first threshold:

reusing a previously downloaded version of a respective document in the plurality of documents instead of downloading a current version of the respective document from a host computer when a difference between the first crawl time and a second crawl time does not exceed a second threshold, or

downloading a current version of the respective document from the host computer when a difference between the first crawl time and a second crawl time exceeds the second threshold.

11. The computer system of claim 9 , the stored data and the one or more programs comprising instructions for:

retrieving, from a first database, at least a subset of contents of a first document in the plurality of documents, the first document corresponding to a document identifier in a first scheduler record, the first scheduler record including a reuse flag for the first document set to a first state; and

retrieving, from a second database, at least a subset of contents of a second document in the plurality of documents, the second document corresponding to a document identifier in a second scheduler record, the second scheduler record including a reuse flag for the second document set to a second state;

wherein the first and second databases are not the same and wherein the second database stores content from previously crawled documents, including the second document.

12. The computer system of claim 11 , wherein the first database includes a set of servers and the set of servers is interconnected by a network.

13. The computer system of claim 11 , wherein the first database includes the World Wide Web.

14. The computer system of claim 11 , wherein the first database includes a subset of the World Wide Web.

15. The computer system of claim 11 , the stored data and one or more programs further comprising instructions for adding the at least a subset of the contents of the first document to the second database.

16. The computer system of claim 9 , wherein the document importance score associated with the document is based, at least in part, on a number of other documents that reference the document.

17. A non-transitory computer-readable storage medium having stored thereon instructions which, when executed by one or more processors of a computer system, cause the one or more processors to perform operations of:

retrieving a plurality of records corresponding to prior scheduled crawls of respective documents in a plurality of documents; and

performing a document crawling operation on the plurality of documents, wherein the document crawling operation includes downloading a current version of a respective document from a host computer based on a determination that a document importance score for the respective document exceeds a first threshold, wherein the document importance score is based on a query-independent metric of an importance of the document for a search engine, or reusing a previously downloaded version of a respective document in the plurality of documents instead of downloading a current version of the respective document from a host computer based on a determination that the document importance score does not exceed a first threshold.

18. The non-transitory computer-readable storage medium of claim 17 , wherein the plurality of records for a respective document include:

a first record including a first document identifier and a first crawl time for the respective document, and

a second record including a second document identifier and a second crawl time for the respective document,

wherein the first document identifier and the second document identifier correspond to the respective document, and

wherein performing the document crawling operation on the plurality of documents further includes, when the document importance score does not exceed the first threshold:

reusing a previously downloaded version of a respective document in the plurality of documents instead of downloading a current version of the respective document from a host computer when a difference between the first crawl time and a second crawl time does not exceed a second threshold, or

downloading a current version of the respective document from the host computer when a difference between the first crawl time and a second crawl time exceeds the second threshold.

19. The non-transitory computer-readable storage medium of claim 17 , wherein the instructions, when executed by the one or more processors, cause the one or more processors to perform operations of:

retrieving, from a first database, at least a subset of contents of a first document in the plurality of documents, the first document corresponding to a document identifier in a first scheduler record, the first scheduler record including a reuse flag for the first document set to a first state; and

retrieving, from a second database, at least a subset of contents of a second document in the plurality of documents, the second document corresponding to a document identifier in a second scheduler record, the second scheduler record including a reuse flag for the second document set to a second state;

wherein the first and second databases are not the same and wherein the second database stores content from previously crawled documents, including the second document.