Hello, Valentin. > I believe we should get rid of this logic and use Ignite schema name as > database name in Spark's catalog.
When I develop Ignite integration with Spark Data Frame I use following
abstraction described by Vladimir Ozerov:
"1) Let's consider Ignite cluster as a single database ("catalog" in ANSI
SQL'92 terms)." [1]
Am I was wrong? If yes - let's fix it.
[1]
http://apache-ignite-developers.2346864.n4.nabble.com/SQL-usability-catalogs-schemas-and-tables-td17148.html
В Ср, 22/08/2018 в 09:26 +0100, Stuart Macdonald пишет:
> Hi Val, yes that's correct. I'd be happy to make the change to have the
> database reference the schema if Nikolay agrees. (I'll first need to do a
> bit of research into how to obtain the list of all available schemata...)
>
> Thanks,
> Stuart.
>
> On Tue, Aug 21, 2018 at 9:43 PM, Valentin Kulichenko <
> valentin.kuliche...@gmail.com> wrote:
>
> > Stuart,
> >
> > Thanks for pointing this out, I was not aware that we use Spark database
> > concept this way. Actually, this confuses me a lot. As far as I understand,
> > catalog is created in the scope of a particular IgniteSparkSession, which
> > in turn is assigned to a particular IgniteContext and therefore single
> > Ignite client. If that's the case, I don't think it should be aware of
> > other Ignite clients that are connected to other clusters. This doesn't
> > look like correct behavior to me, not to mention that with this approach
> > having multiple databases would be a very rare case. I believe we should
> > get rid of this logic and use Ignite schema name as database name in
> > Spark's catalog.
> >
> > Nikolay, what do you think?
> >
> > -Val
> >
> > On Tue, Aug 21, 2018 at 8:17 AM Stuart Macdonald <stu...@stuwee.org>
> > wrote:
> >
> > > Nikolay, Val,
> > >
> > > The JDBC Spark datasource[1] -- as far as I can tell -- has no
> > > ExternalCatalog implementation, it just uses the database specified in the
> > > JDBC URL. So I don't believe there is any way to call listTables() or
> > > listDatabases() for JDBC provider.
> > >
> > > The Hive ExternalCatalog[2] makes the distinction between database and
> > > table using the actual database and table mechanisms built into the
> > > catalog, which is fine because Hive has the clear distinction and
> > > hierarchy
> > > of databases and tables.
> > >
> > > *However* Ignite already uses the "database" concept in the Ignite
> > >
> > > ExternalCatalog[3] to mean the name of an Ignite instance. So in Ignite we
> > > have instances containing schemas containing tables, and Spark only has
> > > the
> > > concept of databases and tables so it seems like either we ignore one of
> > > the three Ignite concepts or combine two of them into database or table.
> > > The current implementation in the pull request combines Ignite schema and
> > > table attributes into the Spark table attribute.
> > >
> > > Stuart.
> > >
> > > [1]
> > > https://github.com/apache/spark/blob/master/sql/core/
> > > src/main/scala/org/apache/spark/sql/execution/
> > > datasources/jdbc/JDBCRelation.scala
> > > [2]
> > > https://github.com/apache/spark/blob/master/sql/hive/
> > > src/main/scala/org/apache/spark/sql/hive/HiveExternalCatalog.scala
> > > [3]
> > > https://github.com/apache/ignite/blob/master/modules/
> > > spark/src/main/scala/org/apache/spark/sql/ignite/
> > > IgniteExternalCatalog.scala
> > >
> > > On Tue, Aug 21, 2018 at 9:31 AM, Nikolay Izhikov <nizhi...@apache.org>
> > > wrote:
> > >
> > > > Hello, Stuart.
> > > >
> > > > Can you do some research and find out how schema is handled in Data
> > >
> > > Frames
> > > > for a regular RDBMS such as Oracle, MySQL, etc?
> > > >
> > > > В Пн, 20/08/2018 в 15:37 -0700, Valentin Kulichenko пишет:
> > > > > Stuart, Nikolay,
> > > > >
> > > > > I see that the 'Table' class (returned by listTables method) has a
> > > >
> > > > 'database' field. Can we use this one to report schema name?
> > > > >
> > > > > In any case, I think we should look into how this is done in data
> > >
> > > source
> > > > implementations for other databases. Any relational database has a
> > >
> > > notion
> > > > of schema, and I'm sure Spark integrations take this into account
> > >
> > > somehow.
> > > > >
> > > > > -Val
> > > > >
> > > > > On Mon, Aug 20, 2018 at 6:12 AM Nikolay Izhikov <nizhi...@apache.org>
> > > >
> > > > wrote:
> > > > > > Hello, Stuart.
> > > > > >
> > > > > > Personally, I think we should change current tables naming and
> > >
> > > return
> > > > table in form of `schema.table`.
> > > > > >
> > > > > > Valentin, could you share your opinion?
> > > > > >
> > > > > >
> > > > > > В Пн, 20/08/2018 в 10:04 +0100, Stuart Macdonald пишет:
> > > > > > > Igniters,
> > > > > > >
> > > > > > > While reviewing the changes for IGNITE-9228 [1,2], Nikolay and I
> > >
> > > are
> > > > > > > discussing whether to introduce a change which may impact
> > >
> > > backwards
> > > > > > > compatibility; Nikolay suggested we take the discussion to this
> > >
> > > list.
> > > > > > >
> > > > > > > Ignite implements a custom Spark catalog which provides an API by
> > > >
> > > > which
> > > > > > > Spark users can list the tables which are available in Ignite
> > >
> > > which
> > > > can be
> > > > > > > queried via Spark SQL. Currently that table name list includes
> > >
> > > just
> > > > the
> > > > > > > names of the tables, but IGNITE-9228 is introducing a change which
> > > >
> > > > allows
> > > > > > > optional prefixing of schema names to table names to disambiguate
> > > >
> > > > multiple
> > > > > > > tables with the same name in different schemas. For the "list
> > > >
> > > > tables" API
> > > > > > > we therefore have two options:
> > > > > > >
> > > > > > > 1. List the tables using both their table names and
> > >
> > > schema-qualified
> > > > table
> > > > > > > names (eg. [ "myTable", "mySchema.myTable" ]) even though they are
> > > >
> > > > the same
> > > > > > > underlying table. This retains backwards compatibility with users
> > >
> > > who
> > > > > > > expect "myTable" to appear in the catalog.
> > > > > > > 2. List the tables using only their schema-qualified names. This
> > > >
> > > > eliminates
> > > > > > > duplication of names in the catalog but will potentially break
> > > > > > > compatibility with users who expect the table name in the catalog.
> > > > > > >
> > > > > > > With either option we will allow for Spark SQL SELECT statements
> > >
> > > to
> > > > use
> > > > > > > either table name or schema-qualified table names, this change
> > >
> > > would
> > > > purely
> > > > > > > impact the API which is used to list available tables.
> > > > > > >
> > > > > > > Any opinions would be welcome.
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Stuart.
> > > > > > >
> > > > > > > [1] https://issues.apache.org/jira/browse/IGNITE-9228
> > > > > > > [2] https://github.com/apache/ignite/pull/4551
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