Motivation

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• Newly created index is in offline state
• offline index cannot be read, only modified (in scope of index rebuild or regular updates)
• index becomes online after index rebuild
• Index may be created on cache start, by DDL command or by API call (direct call to IndexManager)
• on index create an Index instance is created using provided factory, this way we may introduce geospatial indexes or prefix trees in future just providing specific factory.
• sorted index represents a database index in terms of SQL and requires hash index created first (if not exists).
• hash index is just a proxy to cache partitions and always online, it represents a table in terms of SQL. This way SQL queries may be executed before index is fully built

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On index create

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1. index created - all indexes and definitions registered on all nodes, all indexes starts applying current updates
2. onIndexCreate() callback executes - index is registered in a query execution engine
3. index rebuild started - index is filling up with existing data
4. index rebuild finished - index is ready to use
5. onIndexStateChange() callback executes - index becomes available for a query execution engine.

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