In short, Ignite replaces H2’s storage level with its own. For example, Ignite implements H2’s Index interface with its own off-heap data structures underneath. When Ignite executes an SQL query, it will ask H2 to process it, then H2 will callback to Ignite’s implementations of H2’s interfaces (such as Index) to actually retrieve the data. I guess the on-heap processing is mostly H2, although there is a lot of work done by Ignite to make the distributed map-reduce work like creating temporary tables for intermediate results.
Stan From: eugene miretsky Sent: 9 октября 2018 г. 21:52 To: user@ignite.apache.org Subject: Re: Role of H2 datbase in Apache Ignite Hello, I have been struggling with this question myself for a while now too. I think the documents are very ambiguous on how exactly H2 is being used. The document that you linked say "Apache Ignite leverages from H2's SQL query parser and optimizer as well as the execution planner. Lastly, H2 executes a query locally on a particular node and passes a local result to a distributed Ignite SQL engine for further processing." And "However, the data, as well as the indexes, are always stored in the Ignite that executes queries in a distributed and fault-tolerant manner which is not supported by H2." To me, this leaves a lot of ambiguity on how H2 is leveraged on a single Ignite node. (I get that the Reduce stage, as well as distributed transactions, are handled by Ignite, but how about the 'map' stage on a single node). How is a query executed on a single node? Example query: Select count(customer_id) from user where (age > 20) group by customer_id What steps are taken? 1. execution plan: H2 creates an execution plan 2. data retrieval: Since data is stored off-heap, it has to be brought into heap. Does H2 have anything to do with this step, or is it only Ignite? When are indexes used for that? 3. Query execution: Once the data is on heap, what executes the Query (the group_by, aggregations, filters that were not handled by indexes, etc.)? H2 or Ignite? On Fri, Sep 21, 2018 at 9:27 AM Mikhail <michael.cherka...@gmail.com> wrote: Hi, Could you please formulate your question? Because right not your message looks like a request for google. I think the following article has answer for your question: https://apacheignite-sql.readme.io/docs/how-ignite-sql-works Thanks, Mike. -- Sent from: http://apache-ignite-users.70518.x6.nabble.com/
