Auto-completion of widely shared search queries

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.

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.