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https://issues.apache.org/jira/browse/DRILL-4963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15854507#comment-15854507
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ASF GitHub Bot commented on DRILL-4963:
---------------------------------------
Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/701#discussion_r99454038
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/FunctionImplementationRegistry.java
---
@@ -140,27 +142,39 @@ public void register(DrillOperatorTable
operatorTable) {
}
/**
- * Using the given <code>functionResolver</code>
- * finds Drill function implementation for given
<code>functionCall</code>.
- * If function implementation was not found,
- * loads all missing remote functions and tries to find Drill
implementation one more time.
+ * First attempts to finds the Drill function implementation that
matches the name, arg types and return type.
+ * If exact function implementation was not found,
+ * syncs local function registry with remote function registry if needed
+ * and tries to find function implementation one more time
--- End diff --
While this sounds pretty good, consider a possible condition. Suppose a
user consistently uses an overloaded method. Every one of those queries will
need to check with ZK. Drill is supposed to handle many concurrent queries.
Each of those will trigger the update. Soon, we'll be pounding on ZK hundreds
of times per second.
The "not found" case was fine to force a sync since a user would not,
presumably, continually issue such queries if the function really were
undefined. But, the overloaded function case is possible, and can lead to
performance issues.
> Issues when overloading Drill native functions with dynamic UDFs
> ----------------------------------------------------------------
>
> Key: DRILL-4963
> URL: https://issues.apache.org/jira/browse/DRILL-4963
> Project: Apache Drill
> Issue Type: Bug
> Components: Functions - Drill
> Affects Versions: 1.9.0
> Reporter: Roman
> Assignee: Arina Ielchiieva
> Fix For: Future
>
> Attachments: subquery_udf-1.0.jar, subquery_udf-1.0-sources.jar,
> test_overloading-1.0.jar, test_overloading-1.0-sources.jar
>
>
> I created jar file which overloads 3 DRILL native functions
> (LOG(VARCHAR-REQUIRED), CURRENT_DATE(VARCHAR-REQUIRED) and
> ABS(VARCHAR-REQUIRED,VARCHAR-REQUIRED)) and registered it as dynamic UDF.
> If I try to use my functions I will get errors:
> {code:xml}
> SELECT CURRENT_DATE('test') FROM (VALUES(1));
> {code}
> Error: FUNCTION ERROR: CURRENT_DATE does not support operand types (CHAR)
> SQL Query null
> {code:xml}
> SELECT ABS('test','test') FROM (VALUES(1));
> {code}
> Error: FUNCTION ERROR: ABS does not support operand types (CHAR,CHAR)
> SQL Query null
> {code:xml}
> SELECT LOG('test') FROM (VALUES(1));
> {code}
> Error: SYSTEM ERROR: DrillRuntimeException: Failure while materializing
> expression in constant expression evaluator LOG('test'). Errors:
> Error in expression at index -1. Error: Missing function implementation:
> castTINYINT(VARCHAR-REQUIRED). Full expression: UNKNOWN EXPRESSION.
> But if I rerun all this queries after "DrillRuntimeException", they will run
> correctly. It seems that Drill have not updated the function signature before
> that error. Also if I add jar as usual UDF (copy jar to
> /drill_home/jars/3rdparty and restart drillbits), all queries will run
> correctly without errors.
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