index-entry-limit Backend configuration property
specifies the maximum number of entries kept in an index record, before the
server stops maintaining that record, begins scanning the whole database, and runs
an expensive unindexed search. If any index keys have already reached this limit,
indexes must be rebuilt before they can be allowed to use a new limit.
index-entry-limit is configured to be larger than 50000, then
any keys that match more than 50000 entries will be stored in a separate database in
an expanded (or "exploded") format.
All keys whose entry count is less than 50000 continue to be stored in one
database in a consolidated format, such that changes to the key require rewriting
all the entry IDs matching the key. All keys whose entry count is greater than
50000 and less than the
index-entry-limit are stored in a
separate database in an exploded format, such that changes to the key require
writing only to the updated entry ID.
For example, as shown in the figure below, the equality index for the
sn attribute is stored in consolidated format, listing each
entry ID for all entries that contain the sn=smith attribute.
index-entry-limit is increased to 100000, any key with
an entry count less than 50000 continues to be stored in consolidated format.
If a key has an entry count greater than 50000, it will be stored in a separate
database where each key is stored with its entry ID individually. The consolidated
format is very efficient for read operations because the server can retrieve a row
of entry IDs at once, while the exploded format is far more efficient for high
volumes of write operations since it avoids large on-disk growth.