Benoît Paris created FLINK-15775:
------------------------------------
Summary: SourceFunctions are instanciated twice when pulled on
from 2 Sinks
Key: FLINK-15775
URL: https://issues.apache.org/jira/browse/FLINK-15775
Project: Flink
Issue Type: Bug
Components: Table SQL / Planner
Affects Versions: 1.9.1, 1.10.0
Reporter: Benoît Paris
Attachments: flink-test-duplicated-sources.zip
When pulled on by two sinks, the SourceFunctions of a TableSource will get
instantiated twice; (and subsequently opened by the parallelism number, which
is expected behavior):
The following will instantiate the FooTableSource's SourceFunction once (OK
behavior, but not the processing we want):
{code:java}
tEnv.registerTableSource("foo_table", new FooTableSource());
Table out0 = tEnv.sqlQuery("SELECT * FROM foo_table WHERE field_1 = 0");
tEnv.registerTableSink("syso_sink_0", new SysoSink());
out0.insertInto("syso_sink_0");
{code}
This will instantiate the FooTableSource's SourceFunction twice (Not OK, as
we're missing half the inputs in each SysoSink):
{code:java}
tEnv.registerTableSource("foo_table", new FooTableSource());
Table out0 = tEnv.sqlQuery("SELECT * FROM foo_table WHERE field_1 = 0");
Table out1 = tEnv.sqlQuery("SELECT * FROM foo_table WHERE field_1 = 1");
tEnv.registerTableSink("syso_sink_0", new SysoSink());
tEnv.registerTableSink("syso_sink_1", new SysoSink());
out0.insertInto("syso_sink_0");
out1.insertInto("syso_sink_1");
{code}
This might not be a problem for Kafka's SourceFunctions, as we can always
reread from a log; but it is a data loss problem when the source data can't be
reproduced.
Actually, this might be me not understanding the API. Is there a way to make
the runtime read from the same opened SourceFunctions?
Attached is Java code that logs the faulty opening of the SourceFunctions,
pom.xml, and logical execution plans for the duplicated case, and the
workaround.
----
Workaround: make a conversion to an appendStream. Somehow this makes the
planner think it has to put a materialization barrier after the Source and read
from that:
{code:java}
tEnv.registerTableSource("foo_table_source", new FooTableSource());
Table sourceTable = tEnv.sqlQuery("SELECT * FROM foo_table_source");
Table appendingSourceTable = tEnv.fromDataStream(
tEnv.toAppendStream(sourceTable, Types.ROW(new String[]{"field_1"}, new
TypeInformation[]{Types.LONG()}))
);
tEnv.registerTable("foo_table", appendingSourceTable);{code}
Best Regards,
Ben
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