[jira] [Created] (IMPALA-5965) Avoid per-value switch on NeedsConversionInline() when decoding dictionary-encoded strings and timestamps

["Tim Armstrong (JIRA)" <ji...@apache.org>]

Tim Armstrong created IMPALA-5965:
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             Summary: Avoid per-value switch on NeedsConversionInline() when decoding dictionary-encoded strings and timestamps
                 Key: IMPALA-5965
                 URL: https://issues.apache.org/jira/browse/IMPALA-5965
             Project: IMPALA
          Issue Type: Bug
          Components: Backend
    Affects Versions: Impala 2.10.0
            Reporter: Tim Armstrong
            Assignee: Tim Armstrong
            Priority: Minor


I noticed a minor inefficiency in the handling of NeedsConversion() in the parquet scanner. In cases where it's not a runtime constant like dictionary-encoded strings and timestamps, we switch per value. This is probably only a few instructions but in this part of the code that matters.

I did a quick benchmark and saw speedups from ~2.25s->2.11s in scan time on this query:
{code}
use tpch_parquet; 
set num_nodes=1;
set mt_dop=1;
select min(l_returnflag), min(l_linestatus) from biglineitem;
summary;
{code}




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