Indexes speed up searches by effectively reducing the number of entries a search has to check to find a match. An index contains a list of values. Each value is associated with a list of entry identifiers. Directory Server can look up entries quickly by using the lists of entry identifiers in indexes. Without an index to manage a list of entries, Directory Server must check every entry in a suffix to find matches for a search.
Directory Server processes each search request as follows:
Directory Server receives a search request from a client.
Directory Server examines the request to confirm that the search can be processed.
If Directory Server cannot perform the search, it returns an error to the client and might refer the search to another instance of Directory Server.
Directory Server determines whether it manages one or more indexes that are appropriate to the search.
If Directory Server manages indexes that are appropriate to the search, the server looks in all of the appropriate indexes for candidate entries. A candidate entry is an entry that might be a match for the search request.
If Directory Server does not manage an index appropriate to the search, the server generates the set of candidate entries by checking all of the entries in the database.
When Directory Server cannot use indexes, this process consumes more time and system resources.
Directory Server examines each candidate entry to determine whether the entry matches the search criteria.
Directory Server returns matching entries to the client application as it finds the entries.
You can optimize search performance by doing the following:
Preventing Directory Server from performing searches on non-indexed entries
Ensuring that cache sizes are appropriately tuned
Limiting the length of an index
For a comprehensive overview of how indexes work, see Chapter 6, Directory Server Indexing, in Sun Java System Directory Server Enterprise Edition 6.1 Reference. For information about defining indexes, see Chapter 12, Directory Server Indexing, in Sun Java System Directory Server Enterprise Edition 6.1 Administration Guide.