Paul Rogers created IMPALA-7899:
-----------------------------------
Summary: RuntimeFilterGenerator uses Preconditions for normal
conditions
Key: IMPALA-7899
URL: https://issues.apache.org/jira/browse/IMPALA-7899
Project: IMPALA
Issue Type: Bug
Components: Frontend
Affects Versions: Impala 3.0
Reporter: Paul Rogers
Assignee: Paul Rogers
The {{RuntimeFilterGenerator.computeTargetExpr()}} checks if a value can be
cast to a given type. It does so by calling {{Expr.castTo()}}, which uses the
following technique to report that the cast is not valid:
{code:java}
Preconditions.checkArgument(targetType.equals(type),
"targetType=" + targetType + " type=" + type);
{code}
This condition occurs in {{PlannerTest}}. So, if I have a breakpoint set to
catch {{Preconditions}} failures, that breakpoint is hit on every run. I have
to remember, "oh, yeah, it is OK that we are violating this invariant."
In general, it is bad practice to use things like {{assert}}, {{Preconditions}}
or unchecked exceptions to report "expected" conditions: it muddies the water
about what is an invariant or is not.
Instead, use a checked, purpose-built exception, such as {{SqlCastException}},
to report such errors, and include comments that the exception will be thrown
for expected illegal casts.
Or, better, restructure the method so that there is one version that is
expected to succeed (the current one), and another that returns null if the
cast is not legal. Have the enforcing version call the returning-null version.
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