What is a Metamorph index?

This is Thunderstone's name for an inverted (search-engine) index on a column of unstructured text, as distinguished from a b-tree (sorted-order) index normally used on numeric or string database fields. This following is somewhat technical and is intended for experienced database programmers.

A Metamorph index is set up and used in a manner analogous to any other database index:

"create metamorph index descriptionindex on products (description)"

As an illustration of the power this provides, consider a typical Texis query of this model:

"select id, name from products where description like 'big fancy gizmo' order by price;"

The Texis database optimizer uses the metamorph index on the description field, along with the B-tree index on the price field, to quickly and efficiently resolve this query. (From a more technical point of view, you'd probably create a single compound index combining the characteristics of those two indexes.)

Any other database, to accomplish something similar, would receive no help from the database optimizer. The text index is a black box to it. It can only hand off the gizmo query to a separate text index; then create a temporary table containing the text-search results; then do a join between that and the table containing the price information.

Texis is the only relational database that can resolve a query of this type without a join. This makes Texis many times more efficient.