Hi devs,
I've updated the wiki according to feedbacks. Please take another look.
Thanks!
On Fri, Jan 10, 2020 at 2:24 PM Bowen Li <bowenl...@gmail.com> wrote:
> Thanks everyone for the prompt feedback. Please see my response below.
>
> > In Postgress, the TIME/TIMESTAMP WITH TIME ZONE has the
> java.time.Instant semantic, and should be mapped to Flink's TIME/TIMESTAMP
> WITH LOCAL TIME ZONE
>
> Zhenghua, you are right that pg's 'timestamp with timezone' should be
> translated into flink's 'timestamp with local timezone'. I don't find 'time
> with (local) timezone' though, so we may not support that type from pg in
> Flink.
>
> > I suggest that the parameters can be completely consistent with the
> JDBCTableSource / JDBCTableSink. If you take a look to JDBC api:
> "DriverManager.getConnection".
> That allow "default db, username, pwd" things optional. They can included
> in URL. Of course JDBC api also allows establishing connections to
> different databases in a db instance. So I think we don't need provide a
> "base_url", we can just provide a real "url". To be consistent with JDBC
> api.
>
> Jingsong, what I'm saying is a builder can be added on demand later if
> there's enough user requesting it, and doesn't need to be a core part of
> the FLIP.
>
> Besides, unfortunately Postgres doesn't allow changing databases via JDBC.
>
> JDBC provides different connecting options as you mentioned, but I'd like
> to keep our design and API simple and having to handle extra parsing logic.
> And it doesn't shut the door for what you proposed as a future effort.
>
> > Since the PostgreSQL does not have catalog but schema under database,
> why not mapping the PG-database to Flink catalog and PG-schema to Flink
> database
>
> Danny, because 1) there are frequent use cases where users want to switch
> databases or referencing objects across databases in a pg instance 2)
> schema is an optional namespace layer in pg, it always has a default value
> ("public") and can be invisible to users if they'd like to as shown in the
> FLIP 3) as you mentioned it is specific to postgres, and I don't feel it's
> necessary to map Postgres substantially different than others DBMSs with
> additional complexity
>
> >'base_url' configuration: We are following the configuration format
> guideline [1] which suggest to use dash (-) instead of underline (_). And
> I'm a little confused the meaning of "base_url" at the first glance,
> another idea is split it into several configurations: 'driver', 'hostname',
> 'port'.
>
> Jark, I agreed we should use "base-url" in yaml config.
>
> I'm not sure about having hostname and port separately because you can
> specify multiple hosts with ports in jdbc, like
> "jdbc:dbms/host1:port1,host2:port2/", for connection failovers. Separating
> them would make configurations harder.
>
> I will add clear doc and example to avoid any possible confusion.
>
> > 'default-database' is optional, then which database will be used or what
> is the behavior when the default database is not selected.
>
> This should be DBMS specific. For postgres, it will be the <access id>
> database.
>
>
> On Thu, Jan 9, 2020 at 9:48 PM Zhenghua Gao <doc...@gmail.com> wrote:
>
>> Hi Bowen, Thanks for driving this.
>> I think it would be very convenience to use tables in external DBs with
>> JDBC Catalog.
>>
>> I have one concern about "Flink-Postgres Data Type Mapping" part:
>>
>> In Postgress, the TIME/TIMESTAMP WITH TIME ZONE has the java.time.Instant
>> semantic,
>> and should be mapped to Flink's TIME/TIMESTAMP WITH LOCAL TIME ZONE
>>
>> *Best Regards,*
>> *Zhenghua Gao*
>>
>>
>> On Fri, Jan 10, 2020 at 11:09 AM Jingsong Li <jingsongl...@gmail.com>
>> wrote:
>>
>> > Hi Bowen, thanks for reply and updating.
>> >
>> > > I don't see much value in providing a builder for jdbc catalogs, as
>> they
>> > only have 4 or 5 required params, no optional ones. I prefer users just
>> > provide a base url without default db, usrname, pwd so we don't need to
>> > parse url all around, as I mentioned jdbc catalog may need to establish
>> > connections to different databases in a db instance,
>> >
>> > I suggest that the parameters can be completely consistent with the
>> > JDBCTableSource / JDBCTableSink.
>> > If you take a look to JDBC api: "DriverManager.getConnection".
>> > That allow "default db, username, pwd" things optional. They can
>> included
>> > in URL. Of course JDBC api also allows establishing connections to
>> > different databases in a db instance.
>> > So I think we don't need provide a "base_url", we can just provide a
>> real
>> > "url".
>> > To be consistent with JDBC api.
>> >
>> > Best,
>> > Jingsong Lee
>> >
>> > On Fri, Jan 10, 2020 at 10:34 AM Jark Wu <imj...@gmail.com> wrote:
>> >
>> > > Thanks Bowen for the reply,
>> > >
>> > > A user-facing JDBCCatalog and 'catalog.type' = 'jdbc' sounds good to
>> me.
>> > >
>> > > I have some other minor comments when I went through the updated
>> > > documentation:
>> > >
>> > > 1) 'base_url' configuration: We are following the configuration format
>> > > guideline [1] which suggest to use dash (-) instead of underline (_).
>> > > And I'm a little confused the meaning of "base_url" at the first
>> > > glance, another idea is split it into several configurations:
>> 'driver',
>> > > 'hostname', 'port'.
>> > >
>> > > 2) 'default-database' is optional, then which database will be used or
>> > what
>> > > is the behavior when the default database is not selected.
>> > >
>> > > 3) a builder for jdbc catalogs: I agree with Jingsong to provide a
>> > builder.
>> > > Because there is optional configuration here (the default database),
>> > > and providind Builder as the API will be easier for evolution, I'm
>> not
>> > > sure we won't add/modify parameters in the future.
>> > >
>> > > [1]:
>> > >
>> > >
>> >
>> https://flink.apache.org/contributing/code-style-and-quality-components.html#configuration-changes
>> > >
>> > > On Fri, 10 Jan 2020 at 04:52, Bowen Li <bowenl...@gmail.com> wrote:
>> > >
>> > > > Hi Jark and Jingsong,
>> > > >
>> > > > Thanks for your review. Please see my reply in line.
>> > > >
>> > > > > why introducing a `PostgresJDBCCatalog`, not a generic
>> `JDBCCatalog`
>> > > > (catalog.type = 'postgres' vs 'jdbc') ?
>> > > >
>> > > > Thanks for the reminding and I looked at JDBCDialect. A generic,
>> > > > user-facing JDBCCatalog with catalog.type = jdbc and find specific
>> db
>> > > > implementations (pg v.s. mysql v.s. ...) is more aligned with how
>> jdbc
>> > > > sink/source is handled, indeed. However, the catalogs would also
>> need
>> > to
>> > > > execute the query and parse query results in a db-dependent way.
>> E.g.
>> > > jdbc
>> > > > catalog needs to establish connections to different databases
>> within a
>> > db
>> > > > instance on demand. So just having JDBCDialect won't be enough.
>> > > >
>> > > > I think we can do the following:
>> > > > - provide a user-facing JDBCCatalog, composing a db-specific impl
>> > like
>> > > > PostgresJDBCCatalog and MySQLJDBCCatalog. Users still specify
>> "jdbc" as
>> > > > type in both Table API and SQL CLI, internally it will create a
>> > > db-specific
>> > > > impl depending on jdbc base url.
>> > > > - some statements can reside in JDBCDialect. Query execution and
>> > result
>> > > > parsing logic would be located in db-specific impls.
>> > > >
>> > > > - We can provide a Builder for Catalog, In my opinion,
>> defaultDatabase,
>> > > > username, pwd can be included in JDBC DB url.
>> > > >
>> > > > I don't see much value in providing a builder for jdbc catalogs, as
>> > they
>> > > > only have 4 or 5 required params, no optional ones. I prefer users
>> just
>> > > > provide a base url without default db, usrname, pwd so we don't
>> need to
>> > > > parse url all around, as I mentioned jdbc catalog may need to
>> establish
>> > > > connections to different databases in a db instance,
>> > > >
>> > > > - About timestamp and time, write down the specific Flink precision
>> of
>> > > > Postgres?
>> > > >
>> > > > I've documented that. It's 0-6
>> > > >
>> > > > - I think there is a part missing in your document, that is how to
>> use
>> > > this
>> > > > catalog. If you can write a complete example, I think it will be
>> much
>> > > > clearer.
>> > > >
>> > > > I added some examples in both table api and SQL Cli. It will be no
>> > > > different from existing catalogs.
>> > > >
>> > > > - So a thing is what TableFactory will this catalog use? For
>> example,
>> > > > JDBCTableSourceSinkFactory has different parameters for source or
>> sink?
>> > > How
>> > > > do you think about it?
>> > > >
>> > > > This catalog will directly call JDBCTableSourceSinkFactory without
>> > going
>> > > > thru service discovery because we are sure it's a jdbc table. I
>> added
>> > it
>> > > to
>> > > > the doc.
>> > > >
>> > > > For the different params besides schema, as we discussed offline,
>> > > > unfortunately we can't do anything right now until Flink DDL/DML are
>> > able
>> > > > to distinguish 3 types of params - external data's metada,
>> source/sink
>> > > > runtime params, and Flink semantics params. The latter two can't be
>> > > > provided by catalogs. The problem is actually general to all
>> catalogs,
>> > > not
>> > > > just JDBCCatalog. I'm pushing for such an effort to solve it. At
>> this
>> > > > moment we can only use some default params for some cases, and the
>> > other
>> > > > cases cannot take advantage of the JDBC catalog and users still
>> have to
>> > > > write DDL manually.
>> > > >
>> > > > Thanks,
>> > > > Bowen
>> > > >
>> > > > On Wed, Jan 8, 2020 at 7:46 PM Jingsong Li <jingsongl...@gmail.com>
>> > > wrote:
>> > > >
>> > > > > Thanks Bowen for driving this,
>> > > > >
>> > > > > +1 for this, The DDL schema definition is a headache for users,
>> and
>> > > > catalog
>> > > > > is a solution to this problem.
>> > > > >
>> > > > > I have some questions and suggestions:
>> > > > >
>> > > > > - We can provide a Builder for Catalog, In my opinion,
>> > defaultDatabase,
>> > > > > username, pwd can be included in JDBC DB url.
>> > > > >
>> > > > > - About timestamp and time, write down the specific Flink
>> precision
>> > of
>> > > > > Postgres?
>> > > > >
>> > > > > - I think there is a part missing in your document, that is how to
>> > use
>> > > > this
>> > > > > catalog. If you can write a complete example, I think it will be
>> much
>> > > > > clearer.
>> > > > >
>> > > > > - So a thing is what TableFactory will this catalog use? For
>> example,
>> > > > > JDBCTableSourceSinkFactory has different parameters for source or
>> > sink?
>> > > > How
>> > > > > do you think about it?
>> > > > >
>> > > > > Best,
>> > > > > Jingsong Lee
>> > > > >
>> > > > > On Thu, Jan 9, 2020 at 11:33 AM Jark Wu <imj...@gmail.com> wrote:
>> > > > >
>> > > > > > Thanks Bowen for driving this.
>> > > > > >
>> > > > > > +1 to this feature.
>> > > > > >
>> > > > > > My concern is that why introducing a `PostgresJDBCCatalog`, not
>> a
>> > > > generic
>> > > > > > `JDBCCatalog` (catalog.type = 'postgres' vs 'jdbc') ?
>> > > > > > From my understanding, JDBC catalog is similar to JDBC
>> source/sink.
>> > > For
>> > > > > > JDBC source/sink, we have a generic
>> > > > > > implementation for JDBC and delegate operations to JDBCDialect.
>> > > > Different
>> > > > > > driver may have different implementation of
>> > > > > > JDBCDialect, e.g `quoteIdentifier()`.
>> > > > > >
>> > > > > > For JDBC catalog, I guess maybe we can do it in the same way,
>> i.e.
>> > a
>> > > > > > generic JDBCCatalog implementation and delegate
>> > > > > > operations to JDBCDialect, and we will have `listDataBase()`,
>> > > > > > `listTables()` interfaces in JDBCDialect. The benefit is that:
>> > > > > > 0) reuse the existing `JDBCDialect`, I guess JDBCCatalog also
>> need
>> > to
>> > > > > quote
>> > > > > > identifiers.
>> > > > > > 1) we can easily to support a new database catalog (e.g. mysql)
>> by
>> > > > > > implementing new dialects (e.g. MySQLDialect).
>> > > > > > 2) this can keep the same behavior as JDBC source/sink, i.e.
>> > > > > > connector.type=jdbc, catalog.type=jdbc
>> > > > > >
>> > > > > > Best,
>> > > > > > Jark
>> > > > > >
>> > > > > >
>> > > > > > On Thu, 9 Jan 2020 at 08:33, Bowen Li <bowenl...@gmail.com>
>> wrote:
>> > > > > >
>> > > > > > > Hi dev,
>> > > > > > >
>> > > > > > > I'd like to kick off a discussion on adding JDBC catalogs,
>> > > > specifically
>> > > > > > > Postgres catalog in Flink [1].
>> > > > > > >
>> > > > > > > Currently users have to manually create schemas in Flink
>> > > source/sink
>> > > > > > > mirroring tables in their relational databases in use cases
>> like
>> > > JDBC
>> > > > > > > read/write and consuming CDC. Many users have complaint about
>> the
>> > > > > > > unnecessary, redundant, manual work. Any mismatch can lead to
>> a
>> > > > failing
>> > > > > > > Flink job at runtime instead of compile time. All these have
>> been
>> > > > quite
>> > > > > > > unpleasant, resulting in a broken user experience.
>> > > > > > >
>> > > > > > > We want to provide a JDBC catalog interface and a Postgres
>> > > > > implementation
>> > > > > > > for Flink as a start to connect to all kinds of relational
>> > > databases,
>> > > > > > > enabling Flink SQL to 1) retrieve table schema automatically
>> > > without
>> > > > > > > requiring user writes duped DDL 2) check at compile time for
>> > schema
>> > > > > > errors.
>> > > > > > > It will greatly streamline user experiences when using Flink
>> to
>> > > deal
>> > > > > with
>> > > > > > > popular relational databases like Postgres, MySQL, MariaDB,
>> AWS
>> > > > Aurora,
>> > > > > > > etc.
>> > > > > > >
>> > > > > > > Note that the problem and solution are actually very general
>> to
>> > > Flink
>> > > > > > when
>> > > > > > > connecting to all kinds of external systems. We just focus on
>> > > solving
>> > > > > > that
>> > > > > > > for relational databases in this FLIP.
>> > > > > > >
>> > > > > > > Thanks,
>> > > > > > > Bowen
>> > > > > > >
>> > > > > > > [1]
>> > > > > > >
>> > > > > > >
>> > > > > >
>> > > > >
>> > > >
>> > >
>> >
>> https://cwiki.apache.org/confluence/display/FLINK/FLIP-92%3A+JDBC+catalog+and+Postgres+catalog
>> > > > > > >
>> > > > > >
>> > > > >
>> > > > >
>> > > > > --
>> > > > > Best, Jingsong Lee
>> > > > >
>> > > >
>> > >
>> >
>> >
>> > --
>> > Best, Jingsong Lee
>> >
>>
>
