Hi Danny,
compared to the hints, FLIP-110 is fully compliant to the SQL standard.
I don't think that `CREATE TEMPORARY TABLE Temp (LIKE t) WITH (k=v)` is
too verbose or awkward for the power of basically changing the entire
connector. Usually, this statement would just precede the query in a
multiline file. So it can be change "in-place" like the hints you proposed.
Many companies have a well-defined set of tables that should be used. It
would be dangerous if users can change the path or topic in a hint. The
catalog/catalog manager should be the entity that controls which tables
exist and how they can be accessed.
> what’s the problem there if we user the table hints to support “start
offset”?
IMHO it violates the meaning of a hint. According to the dictionary, a
hint is "a statement that expresses indirectly what one prefers not to
say explicitly". But offsets are a property that are very explicit.
If we go with the hint approach, it should be expressible in the
TableSourceFactory which properties are supported for hinting. Or do you
plan to offer those hints in a separate Map<String, String> that cannot
overwrite existing properties? I think this would be a different story...
Regards,
Timo
On 10.03.20 10:34, Danny Chan wrote:
Thanks Timo ~
Personally I would say that offset > 0 and start offset = 10 does not have the
same semantic, so from the SQL aspect, we can not implement a “starting offset”
hint for query with such a syntax.
And the CREATE TABLE LIKE syntax is a DDL which is just verbose for defining
such dynamic parameters even if it could do that, shall we force users to
define a temporal table for each query with dynamic params, I would say it’s an
awkward solution.
"Hints should give "hints" but not affect the actual produced result.” You
mentioned that multiple times and could we give a reason, what’s the problem there if we user
the table hints to support “start offset” ? From my side I saw some benefits for that:
• It’s very convent to set up these parameters, the syntax is very much like
the DDL definition
• It’s scope is very clear, right on the table it attathed
• It does not affect the table schema, which means in order to specify the
offset, there is no need to define an offset column which is weird actually,
offset should never be a column, it’s more like a metadata or a start option.
So in total, FLIP-110 uses the offset more like a Hive partition prune, we can
do that if we have an offset column, but most of the case we do not define
that, so there is actually no conflict or overlap.
Best,
Danny Chan
在 2020年3月10日 +0800 PM4:28，Timo Walther <twal...@apache.org>，写道：
Hi Danny,
shouldn't FLIP-110[1] solve most of the problems we have around defining
table properties more dynamically without manual schema work? Also
offset definition is easier with such a syntax. They must not be defined
in catalog but could be temporary tables that extend from the original
table.
In general, we should aim to keep the syntax concise and don't provide
too many ways of doing the same thing. Hints should give "hints" but not
affect the actual produced result.
Some connector properties might also change the plan or schema in the
future. E.g. they might also define whether a table source supports
certain push-downs (e.g. predicate push-down).
Dawid is currently working a draft that might makes it possible to
expose a Kafka offset via the schema such that `SELECT * FROM Topic
WHERE offset > 10` would become possible and could be pushed down. But
this is of course, not planned initially.
Regards,
Timo
[1]
https://cwiki.apache.org/confluence/display/FLINK/FLIP-110%3A+Support+LIKE+clause+in+CREATE+TABLE
On 10.03.20 08:34, Danny Chan wrote:
Thanks Wenlong ~
For PROPERTIES Hint Error handling
Actually we have no way to figure out whether a error prone hint is a
PROPERTIES hint, for example, if use writes a hint like ‘PROPERTIAS’, we do not
know if this hint is a PROPERTIES hint, what we know is that the hint name was
not registered in our Flink.
If the user writes the hint name correctly (i.e. PROPERTIES), we did can
enforce the validation of the hint options though the pluggable
HintOptionChecker.
For PROPERTIES Hint Option Format
For a key value style hint option, the key can be either a simple identifier or
a string literal, which means that it’s compatible with our DDL syntax. We
support simple identifier because many other hints do not have the component
complex keys like the table properties, and we want to unify the parse block.
Best,
Danny Chan
在 2020年3月10日 +0800 PM3:19，wenlong.lwl <wenlong88....@gmail.com>，写道：
Hi Danny, thanks for the proposal. +1 for adding table hints, it is really
a necessary feature for flink sql to integrate with a catalog.
For error handling, I think it would be more natural to throw an
exception when error table hint provided, because the properties in hint
will be merged and used to find the table factory which would cause an
exception when error properties provided, right? On the other hand, unlike
other hints which just affect the way to execute the query, the property
table hint actually affects the result of the query, we should never ignore
the given property hints.
For the format of property hints, currently, in sql client, we accept
properties in format of string only in DDL: 'connector.type'='kafka', I
think the format of properties in hint should be the same as the format we
defined in ddl. What do you think?
Bests,
Wenlong Lyu
On Tue, 10 Mar 2020 at 14:22, Danny Chan <yuzhao....@gmail.com> wrote:
To Weike: About the Error Handing
To be consistent with other SQL vendors, the default is to log warnings
and if there is any error (invalid hint name or options), the hint is just
ignored. I have already addressed in the wiki.
To Timo: About the PROPERTIES Table Hint
• The properties hints is also optional, user can pass in an option to
override the table properties but this does not mean it is required.
• They should not include semantics: does the properties belong to
semantic ? I don't think so, the plan does not change right ? The result
set may be affected, but there are already some hints do so, for example,
MS-SQL MAXRECURSION and SNAPSHOT hint [1]
• `SELECT * FROM t(k=v, k=v)`: this grammar breaks the SQL standard
compared to the hints way(which is included in comments)
• I actually didn't found any vendors to support such grammar, and there
is no way to override table level properties dynamically. For normal RDBMS,
I think there are no requests for such dynamic parameters because all the
table have the same storage and computation and they are almost all batch
tables.
• While Flink as a computation engine has many connectors, especially for
some message queue like Kafka, we would have a start_offset which is
different each time we start the query, such parameters can not be
persisted to catalog, because it’s not static, this is actually the
background we propose the table hints to indicate such properties
dynamically.
To Jark and Jinsong: I have removed the query hints part and change the
title.
[1]
https://docs.microsoft.com/en-us/sql/t-sql/queries/hints-transact-sql-query?view=sql-server-ver15
Best,
Danny Chan
在 2020年3月9日 +0800 PM5:46，Timo Walther <twal...@apache.org>，写道：
Hi Danny,
thanks for the proposal. I agree with Jark and Jingsong. Planner hints
and table hints are orthogonal topics that should be discussed
separately.
I share Jingsong's opinion that we should not use planner hints for
passing connector properties. Planner hints should be optional at any
time. They should not include semantics but only affect execution time.
Connector properties are an important part of the query itself.
Have you thought about options such as `SELECT * FROM t(k=v, k=v)`? How
are other vendors deal with this problem?
Regards,
Timo
On 09.03.20 10:37, Jingsong Li wrote:
Hi Danny, +1 for table hints, thanks for driving.
I took a look to FLIP, most of content are talking about query hints.
It is
hard to discussion and voting. So +1 to split it as Jark said.
Another thing is configuration that suitable to config with table
hints:
"connector.path" and "connector.topic", Are they really suitable for
table
hints? Looks weird to me. Because I think these properties are the
core of
table.
Best,
Jingsong Lee
On Mon, Mar 9, 2020 at 5:30 PM Jark Wu <imj...@gmail.com> wrote:
Thanks Danny for starting the discussion.
+1 for this feature.
If we just focus on the table hints not the query hints in this
release,
could you split the FLIP into two FLIPs?
Because it's hard to vote on partial part of a FLIP. You can keep
the table
hints proposal in FLIP-113 and move query hints into another FLIP.
So that we can focuse on the table hints in the FLIP.
Thanks,
Jark
On Mon, 9 Mar 2020 at 17:14, DONG, Weike <kyled...@connect.hku.hk>
wrote:
Hi Danny,
This is a nice feature, +1.
One thing I am interested in but not mentioned in the proposal is
the
error
handling, as it is quite common for users to write inappropriate
hints in
SQL code, if illegal or "bad" hints are given, would the system
simply
ignore them or throw exceptions?
Thanks : )
Best,
Weike
On Mon, Mar 9, 2020 at 5:02 PM Danny Chan <yuzhao....@gmail.com>
wrote:
Note:
we only plan to support table hints in Flink release 1.11, so
please
focus
mainly on the table hints part and just ignore the planner
hints, sorry
for
that mistake ~
Best,
Danny Chan
在 2020年3月9日 +0800 PM4:36，Danny Chan <yuzhao....@gmail.com>，写道：
Hi, fellows ~
I would like to propose the supports for SQL hints for our
Flink SQL.
We would support hints syntax as following:
select /*+ NO_HASH_JOIN, RESOURCE(mem='128mb',
parallelism='24') */
from
emp /*+ INDEX(idx1, idx2) */
join
dept /*+ PROPERTIES(k1='v1', k2='v2') */
on
emp.deptno = dept.deptno
Basically we would support both query hints(after the SELECT
keyword)
and table hints(after the referenced table name), for 1.11, we
plan to
only
support table hints with a hint probably named PROPERTIES:
table_name /*+ PROPERTIES(k1='v1', k2='v2') *+/
I am looking forward to your comments.
You can access the FLIP here:
https://cwiki.apache.org/confluence/display/FLINK/FLIP-113%3A+SQL+and+Planner+Hints
Best,
Danny Chan
