Auto-completion of widely shared search queries

1. A method comprising:

maintaining a prefix index that includes a plurality of prefix index entries, wherein each prefix index entry includes a prefix, a group identifier that identifies a group of users that have access to a particular one of the documents, and a portion of the particular document extracted from the particular document and that begins with the prefix, and associates the prefix with the group identifier, and associates the portion of the particular document with the prefix and the group identifier;

receiving input from a user that is associated with a search field;

determining a user identifier associated with the user that submitted the received input;

mapping the user identifier to a particular group identifier that is associated with the user;

obtaining multiple candidate query suggestions based on the received input and the prefix index by identifying a subset of prefix index entries having a prefix that corresponds to the received input, each candidate query suggestion being the portion of the particular document for a prefix index entry of the subset of prefix index entries;

selecting a subset of the candidate query suggestions based on the particular group identifier that is associated with the user, the selection comprising including in the subset candidate query suggestion that are associated with the particular group identifier that is associated with the user, and excluding from the subset candidate query suggestion that are not associated with the particular group identifier that is associated with the user; and

providing the subset of candidate query suggestions to the user as suggested queries.

2. The method of claim 1 , wherein the input from the user that is associated with the search field includes a zero character input.

3. The method of claim 1 , wherein the input from the user that is associated with the search field includes a single character.

4. The method of claim 1 , the method further comprising:

receiving two or more inputs from the user that are associated with the search field; and

for each received input from the user:

determining a user identifier associated with the user that submitted the received input;

mapping the user identifier to a particular group identifier that is associated with the user;

obtaining one or multiple candidate query suggestions based on the received input and the prefix index;

selecting a subset of the candidate query suggestions based on the particular group identifier that is associated with the user; and

providing the subset of candidate query suggestions to the user as suggested queries.

5. The method of claim 1 , wherein selecting a subset of candidate queries based on the group identifier includes:

determining a subset of prefix index entries that are associated with prefix that corresponds to the received input; and

for each prefix index entry:

determining whether the particular group identifier that is associated with the user corresponds to a group identifier associated with the prefix index entry; and

in response to a determination that the particular group identifier that is associated with the user corresponds to the group identifier associated with the prefix index entry, selecting the portion of the document that is associated with the prefix index entry for inclusion as a candidate query in the subset of candidate queries.

6. The method of claim 1 , further comprising:

generating a group score that is associated with each candidate query suggestion and unique to each particular group; and

ranking the suggested queries based on the group score.

7. The method of claim 1 ,

wherein the candidate query includes one or multiple words,

wherein the group score is based on the number of times the one or multiple words appear in documents associated with each respective group of users.

8. A system comprising:

one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising:

maintaining a prefix index that includes a plurality of prefix index entries, wherein each prefix index entry includes a prefix, a group identifier that identifies a group of users that have access to a particular one of the documents, and a portion of the particular document extracted from the particular document and that begins with the prefix, and associates the prefix with the group identifier, and associates the portion of the particular document with the prefix and the group identifier;

receiving input from a user that is associated with a search field;

determining a user identifier associated with the user that submitted the received input;

mapping the user identifier to a particular group identifier that is associated with the user;

obtaining multiple candidate query suggestions based on the received input and the prefix index by identifying a subset of prefix index entries having a prefix that corresponds to the received input, each candidate query suggestion being the portion of the particular document for a prefix index entry of the subset of prefix index entries;

selecting a subset of the candidate query suggestions based on the particular group identifier that is associated with the user, the selection comprising including in the subset candidate query suggestion that are associated with the particular group identifier that is associated with the user, and excluding from the subset candidate query suggestion that are not associated with the particular group identifier that is associated with the user; and

providing the subset of candidate query suggestions to the user as suggested queries.

9. The system of claim 8 , wherein the input from the user that is associated with the search field includes a zero character input.

10. The system of claim 8 , wherein the input from the user that is associated with the search field includes a single character.

11. The system of claim 8 , the operations further comprising:

receiving two or more inputs from the user that are associated with the search field; and

for each received input from the user:

determining a user identifier associated with the user that submitted the received input;

mapping the user identifier to a particular group identifier that is associated with the user;

obtaining one or multiple candidate query suggestions based on the received input and the prefix index;

selecting a subset of the candidate query suggestions based on the particular group identifier that is associated with the user; and

providing the subset of candidate query suggestions to the user as suggested queries.

12. The system of claim 8 , wherein selecting a subset of candidate queries based on the group identifier includes:

determining a subset of prefix index entries that are associated with prefix that corresponds to the received input; and

for each prefix index entry:

determining whether the particular group identifier that is associated with the user corresponds to a group identifier associated with the prefix index entry; and

in response to a determination that the particular group identifier that is associated with the user corresponds to the group identifier associated with the prefix index entry, selecting the portion of the document that is associated with the prefix index entry for inclusion as a candidate query in the subset of candidate queries.

13. The system of claim 8 , the operations further comprising:

generating a group score that is associated with each candidate query suggestion and unique to each particular group; and

ranking the suggested queries based on the group score,

wherein the candidate query includes one or multiple words,

wherein the group score is based on the number of times the one or multiple words appear in documents associated with each respective group of users.

14. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising:

maintaining a prefix index that includes a plurality of prefix index entries, wherein each prefix index entry includes a prefix, a group identifier that identifies a group of users that have access to a particular one of the documents, and a portion of the particular document extracted from the particular document and that begins with the prefix, and associates the prefix with the group identifier, and associates the portion of the particular document with the prefix and the group identifier;

receiving input from a user that is associated with a search field;

determining a user identifier associated with the user that submitted the received input;

mapping the user identifier to a particular group identifier that is associated with the user;

obtaining multiple candidate query suggestions based on the received input and the prefix index by identifying a subset of prefix index entries having a prefix that corresponds to the received input, each candidate query suggestion being the portion of the particular document for a prefix index entry of the subset of prefix index entries;

selecting a subset of the candidate query suggestions based on the particular group identifier that is associated with the user, the selection comprising including in the subset candidate query suggestion that are associated with the particular group identifier that is associated with the user, and excluding from the subset candidate query suggestion that are not associated with the particular group identifier that is associated with the user; and

providing the subset of candidate query suggestions to the user as suggested queries.

15. The computer-readable medium of claim 14 , wherein the input from the user that is associated with the search field includes a zero character input.

16. The computer-readable medium of claim 14 , wherein the input from the user that is associated with the search field includes a single character.

17. The computer-readable medium of claim 14 , the operations further comprising:

receiving two or more inputs from the user that are associated with the search field; and

for each received input from the user:

determining a user identifier associated with the user that submitted the received input;

mapping the user identifier to a particular group identifier that is associated with the user;

obtaining one or multiple candidate query suggestions based on the received input and the prefix index;

selecting a subset of the candidate query suggestions based on the particular group identifier that is associated with the user; and

providing the subset of candidate query suggestions to the user as suggested queries.

18. The computer-readable medium of claim 14 , wherein selecting a subset of candidate queries based on the group identifier includes:

determining a subset of prefix index entries that are associated with prefix that corresponds to the received input; and

for each prefix index entry:

determining whether the particular group identifier that is associated with the user corresponds to a group identifier associated with the prefix index entry; and

in response to a determination that the particular group identifier that is associated with the user corresponds to the group identifier associated with the prefix index entry, selecting the portion of the document that is associated with the prefix index entry for inclusion as a candidate query in the subset of candidate queries.