Indexes

ActiveSpaces automatically builds a distributed, in-memory index of the tuples in the space when a space is created or loaded. Because indexes are stored in memory, queries locate matching records more quickly because the queries do not have to iterate through every record.

Using indexes, ActiveSpaces also allows you to query for any field of the records contained in the space, and the queries can be serviced faster if indexes are built on the fields used by the query filter statement.

Indexes can be either hash indexes (the default) or tree type indexes, and can contain one or more fields.

• A hash index is more efficient if the set of values to be stored is randomly distributed or the query is selecting for specific values rather than ranges of values.
• A tree index is more efficient when the query is selecting ordered ranges of values.

ActiveSpaces allows you to define as many indexes as you want on a space, as required, depending on the types of queries that will be run over the space. Indexes are part of the space's definition and are built on one or more of the fields that are defined for the space. You can build indexes on any of the fields defined for the space. Indexes have a type, which can be either “HASH” or “TREE.” Hash indexes speed up queries where the filter is an exact match ('=' operator) of a value to the field, e.g.: “field = value”. Tree indexes speed up queries where the filter is a range match ('>', '<', '>=', '<=' operators) of a value to the field, e.g. “field > value.”

If your query filter uses only one field, then you can speed it up by defining an index just on the field that it uses. If your query filter uses more than one field, then you can speed it up by creating a 'composite index' on the fields used in the filter. In this case the order of the fields when the index is defined matters when the TREE index type is used and the query filter contains both equality and range operators separated by 'AND': for example if the query is “field1 = value1 and field2 = value2 and field3 > value3” then in order to benefit from the index, it should be defined on fields “field1”,”field2,”field3” in that order (and only in that order).

A particular field can be used in more than one index, for example if two query filters such as “field = value” and “field > value” are to be used, then you could define two indexes on the field in question: one of type 'HASH' and the other one of type 'TREE,' and the ActiveSpaces query optimizer will automatically use the appropriate index depending on the query being issued.

There is always an index automatically created on the key fields of the space, this index is of type HASH by default (but can be changed to a TREE type if needed).