Netscape NETSCAPE DIRECTORY SERVER 6.02, Administrator'S Manual

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Managing Indexes
368 Netscape Directory Server Administrator’s Guide • May 2002
When All IDs Threshold is Too Low
When you set the All IDs Threshold too low, too many index keys will contain the
All IDs token. This can result in too many directory searches examining every entry
in your directory. The performance hit on searches can be considerable.
For example, suppose you are managing an equality index on the common name
(
cn
) attribute. One of the index keys stored in your
cn
index is
cn=James
. The
corresponding entry ID list contains the ID number of every entry containing an
attribute that is set to
James
.
The equality index on the
cn
attribute is easy to maintain because only small
fraction of the entries in your directory will include
cn=James
. Performance for
searches that use a
cn=James
filter will be improved because only that small
fraction of entry IDs needs to be examined when servicing the search request.
However, over time your directory may continue to grow. As it does, more and
more
James
may be added, but at the same relatively small proportion of total
directory entries. Eventually, the
cn=James
entry ID list can become quite large,
but it will still be a list that is necessary for search performance. If your directory
grows large enough that so many
cn=James
entries are added that the All IDs
threshold is met, then the
cn=James
entry ID list is replaced with an All IDs token.
Every time you search for
cn=James
, the Directory Server will examine every
single entry in the directory in response to the search request.
When the database grows large, the All IDs threshold will be set for a large
percentage of all index keys and your search performance will significantly
degrade.
When All IDs Threshold is Too High
Setting the All IDs Threshold too high can also cause performance problems. An
excessively high All IDs Threshold results in large entry ID lists that must be
maintained and loaded into memory when servicing search requests. An
excessively high All IDs Threshold can eliminate all of the benefits of the All IDs
mechanism (see “Benefits of the All IDs Mechanism,” on page 367 for details).
All IDs Threshold Tuning Advice for Single-
Enterprise Directories
Be careful when changing the default All IDs Threshold value for your server. If
you change the threshold to an inappropriate value, you can compromise rather
than improve your server performance. This tuning advice is intended primarily
for single-enterprise directories of up to 80,000 entries.