Taras Bobrovytsky 575b5a20e6 IMPALA-5017: Error on decimal overflow ...

Before this patch, decimal operations would either silently overflow (in
the case of sum() and avg()), or produce a warning.

In this patch, the behaviour is changed so that an error is produced in
the case of overflow when DECIMAL_v2 is enabled. Decimal v1 behaviour is
unchanged.

We introduce overflow checks when computing sum() and avg(). This
results in a ~30% performance regression when we are in decimal v2 mode
compared to decimal v1.

Benchmarks:
  Query:
  select sum(dec_38_19) from decimal_tbl
    Decimal v1: 11.57s
    Decimal v2: 16.58s

  Query:
  select avg(dec_38_19) from decimal_tbl
    Decimal v1: 12.08s
    Decimal v2: 17.08s

The performance regression is not as bad if we are computing the sum or
average of decimal column with a lower precision:

  Query:
  select sum(dec_9_5) from decimal_tbl
    Decimal v1: 11.06s
    Decimal v2: 13.08s

  Query:
  select avg(dec_9_5) from decimal_tbl
    Decimal v1: 11.56s
    Decimal v2: 13.57s

Testing:
- Added several end to end tests.
- Updated Expr tests to check for error in case of overflow.

Change-Id: Id98a92c9a9469ec8cf14e518c741a2dab7053019
Reviewed-on: http://gerrit.cloudera.org:8080/8404
Reviewed-by: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Tested-by: Impala Public Jenkins

2017-12-01 23:23:01 +00:00

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