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https://issues.apache.org/jira/browse/FLINK-21573?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17347654#comment-17347654
]
Qishang Zhong commented on FLINK-21573:
---------------------------------------
Hi [~lzljs3620320] . In this case, UDF `split_str` will be called twice.
{code:java}
//代码占位符
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env =
StreamExecutionEnvironment.getExecutionEnvironment();
EnvironmentSettings settings =
EnvironmentSettings.newInstance().inStreamingMode().useBlinkPlanner().build();
StreamTableEnvironment tEnv = StreamTableEnvironment.create(env, settings);
DataStream<Order> orderA =
env.fromCollection(
Arrays.asList(
new Order(1L, "beer", 3)));
Table tableA = tEnv.fromDataStream(orderA, $("user"), $("product"),
$("amount"));
tEnv.createTemporaryFunction("split_str", new SubstringFunction());
Table table =
tEnv.sqlQuery("SELECT user, product, amount, d, UPPER(d) as e\n" +
"FROM (\n" +
" SELECT split_str(product,1,2) as d, *\n" +
" FROM " + tableA + "\n" +
") T");
tEnv.toAppendStream(table, Row.class).print();
env.execute();
}
public static class Order {
public Long user;
public String product;
public int amount;
public Order() {
}
public Order(Long user, String product, int amount) {
this.user = user;
this.product = product;
this.amount = amount;
}
}
public static class SubstringFunction extends ScalarFunction {
public String eval(String s, Integer begin, Integer end) {
System.out.println(s);
return s.substring(begin, end);
}
}
{code}
I have some ETL jobs need to connect jdbc or RPC calls in the UDF. It will have
a big effect.
> Support expression reuse in codegen
> -----------------------------------
>
> Key: FLINK-21573
> URL: https://issues.apache.org/jira/browse/FLINK-21573
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Runtime
> Reporter: Benchao Li
> Priority: Major
>
> Currently there is no expression reuse in codegen, and this may result in
> more CPU overhead in some cases. E.g.
> {code:java}
> SELECT my_map['key1'] as key1, my_map['key2'] as key2, my_map['key3'] as key3
> FROM (
> SELECT dump_json_to_map(col1) as my_map
> FROM T
> )
> {code}
> `dump_json_to_map` will be called 3 times.
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