[IMPALA-2379] Constant argument for UDAF is not accessible in Init function.

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Impala 2.2
• Fix Version/s: Impala 2.8.0
• Component/s: Frontend
• Labels: ramp-up
• Target Version: Product Backlog
• Assignee: Chris Channing
• Reporter: Tim Armstrong
• Created: 21/Sep/15 18:16
• Updated: 04/Jan/17 23:58
• Resolved: 08/Nov/16 04:08

Description

A user reported on the user list that they were unable to access a constant argument from the Init function of a UDAF. It would be convenient in many cases to support this.

I'm adding a parameter to my version of the appx_median function to set the number of samples we want to store. My plan was to require that the number of samples parameter be a constant so I can allocate the memory for the samples in the Init function but I can't seem to access it in the Init function.

  if (! ctx->IsArgConstant(1)) {
    ctx->SetError("The number of samples must be a constant");
    return;

  }

If I include that check in my Init function, it always returns an error and I get back a NULL when I try to access the constant arg:

int max_samples = reinterpret_cast<IntVal*>(ctx->GetConstantArg(1))->val;