[IMPALA-5939] StringConcatUpdate() UDA example uses StringVal::CopyFrom() incorrectly.

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: Impala 2.10.0
• Component/s: Backend
• Target Version: Product Backlog
• Epic Color: ghx-label-2
• Assignee: Unassigned
• Reporter: Tim Armstrong
• Created: 14/Sep/17 21:35
• Updated: 14/Sep/17 21:35

Description

http://community.cloudera.com/t5/Interactive-Short-cycle-SQL/Memory-handling-in-Impala-UDA-functions/m-p/59877#M3574?eid=1&aid=1 pointed out that StringConcatUpdate() uses a local allocation to store the intermediate value (returned from StringVal::CopyFrom()) when it show be using a non-local allocation from Allocate().

void StringConcatUpdate(FunctionContext* context, const StringVal& arg1,
    const StringVal& arg2, StringVal* val) {
  if (val->is_null) {
    val->is_null = false;
    *val = StringVal::CopyFrom(context, arg1.ptr, arg1.len);
  } else {
    int new_len = val->len + arg1.len + arg2.len;
    StringVal new_val(context, new_len);
    if (!new_val.is_null) {
      memcpy(new_val.ptr, val->ptr, val->len);
      memcpy(new_val.ptr + val->len, arg2.ptr, arg2.len);
      memcpy(new_val.ptr + val->len + arg2.len, arg1.ptr, arg1.len);
    }
    *val = new_val;
  }
}

The bug was fixed in a different repo years ago.
https://github.com/cloudera/impala-udf-samples/commit/3fce648fddb6c41e09572e0de89d3a83b394d47a