Pranav, You can reference Calcite adaptors implementation, such as JDBC Adaptor[1], MongoDB Adaptor[2]. Their implementation allows pushing down operations (RelNode) to the adapter as much as possible, and the left RelNodes will be implemented using Enumerable Convention.
We have a Converter[3] concept which makes this possible. The converter node allows multiple Conventions in a single query. This also answers your second question. There is a talk[4] about this, it's very helpful for understanding this concept. [1] https://github.com/apache/calcite/blob/main/core/src/main/java/org/apache/calcite/adapter/jdbc/JdbcToEnumerableConverter.java [2] https://github.com/apache/calcite/blob/main/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoToEnumerableConverter.java [3] https://github.com/apache/calcite/blob/main/core/src/main/java/org/apache/calcite/rel/convert/Converter.java [4] https://calcite.apache.org/community/#fast-federated-sql-with-apache-calcite Julian Hyde <[email protected]> 于2022年8月6日周六 02:06写道： > Pranav, > > Please subscribe to this list. You have asked several questions, received > replies, not acknowledged those replies, and asked further questions. Also, > since you are not subscribed, each email you post has to go through manual > moderation. > > Julian > > > On Aug 5, 2022, at 9:38 AM, Pranav Deshpande < > [email protected]> wrote: > > > > Dear Apache Calcite Team, > > I have 2 questions. > > > > --------------------------------- > > 1. > > > > There are plenty of examples on how to push down projects and filters > into > > the leaf nodes (tablescans). > > > > However, I could not find any examples to push down joins to TableScans > (or > > joins+filters+projects etc.) [this is helpful for data federation I > think]. > > > > On the mailing list, many folks are suggesting that I use Drill. However, > > the purpose of my exercise is to gain knowledge about DBMS and Query > > processing etc. > > > > I tried debugging open source engines that use Calcite (Drill, Druid, > Trino > > etc.) but was completely lost. > > > > Any examples/pointers/guidance around the same would be appreciated. > > Example, pushing down a join with a filter to a DBMS(consider jdbc > > msql etc.) > > > > ------------------------------------- > > 2. > > > > The 2nd question I have is regarding conventions and different DBMS. The > > cluster has a method to replace the trait convention(Bindable,JDBC etc.), > > and then we optimize and get the physical plan. > > > > But imagine I have both the MYSQL JDBC convnction and a cassandra > > convention and some user is trying to query both tables. > > > > Something like "SELECT users.username, specialdata.country from > > cassandraDB.user join mysqlDB.specialdata ON users.id > =specialdata.userid" > > > > Now, how will calcite do the optimization here? The planner is not > > accepting 2 different conventions. > > > > Thanks & Regards, > > Pranav > > -- Best, Benchao Li
