Query Evaluation According to the Lowest Common Denominator
When queries are evaluated, they use the index settings that are calculated for the database at a given time. The current index settings for a query are determined at the time of query evaluation, and are based on the lowest common denominator of (that is, the index/fragmentation settings that are the least of) the following:
The index/fragmentation settings defined in the database configuration.
The actual index/fragmentation of documents/fragments in the database.
At any given time, the current lowest common denominator is invalidated upon the following events:
system startup
a change to the database configuration settings
when a reindexing operation completes
If the lowest common denominator is invalidated, it is recalculated the next time a query is issued against the database.
The net impact is that, when index/fragmentation settings have changed on a database after any data is loaded, queries cannot take advantage of the new settings until the new settings meet the lowest common denominator criteria. Depending on the types of index setting changes you make, this can cause queries that behaved one way before index settings were changed to behave differently after the changes. The next section provides a sample scenario to help illustrate this behavior.