Thanks! So does it mean that CacheConfiguration.queryParallelism is really an H2 settings?
On Tue, Oct 9, 2018 at 4:27 PM Stanislav Lukyanov <stanlukya...@gmail.com> wrote: > 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 <eugene.miret...@gmail.com> > *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/ > > >
