Hi Igor, Local queries feature is broadly used together with affinity-based compute tasks: https://apacheignite.readme.io/docs/collocate-compute-and-data#section-affinity-call-and-run-methods
The use case is as follows. The user knows that all required data needed for computation is collocated, and SQL is used as an advanced API for data retrieval from the computation code. The affinity task ensures that partitions won't be discarded from the node(s) if the topology changes during the task execution and, thus, it's safe to run SQL locally skipping distributed phases. The combination of affinity compute tasks with local SQL is a real and valuable use case, and this is what we need to support with Calcite. Do you see any challenges? - Denis On Fri, Nov 1, 2019 at 8:46 AM Roman Kondakov <kondako...@mail.ru.invalid> wrote: > Hi Igor! > > IMO we need to maintain the backward compatibility between old and new > query engines as much as possible. And therefore we shouldn't change the > behavior of local queries. > > So, for local queries Calcite's planner shouldn't consider the > distribution trait at all. > > > -- > Kind Regards > Roman Kondakov > > On 01.11.2019 17:07, Seliverstov Igor wrote: > > Hi Igniters, > > > > Working on new generation of Ignite SQL I faced a question: «Do we need > local queries at all and, if so, what semantic they should have?». > > > > Current planing flow consists of next steps: > > > > 1) Parsing SQL to AST > > 2) Validating AST (against Schema) > > 3) Optimizing (Building execution graph) > > 4) Splitting (into query fragments which executes on target nodes) > > 5) Mapping (query fragments to nodes/partitions) > > > > At last step we check that all Fragment sources (a table or result) have > the same distribution (in other words all sources have to be co-located) > > > > Planner and Splitter guarantee that all caches in a Fragment are > co-located, an Exchange is produced otherwise. But if we force local > execution we cannot produce Exchanges, that means we may face two > non-co-located caches inside a single query fragment (result of local query > planning is a single query fragment). So, we cannot pass the check. > > > > Should we throw an exception or omit the check for local query planning > or prohibit local queries at all? > > > > Your thoughts? > > > > Regards, > > Igor >
