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Date: Thu, 2 Mar 2017 00:11:38 +0000
From: "Zach Amsden (Code Review)" <gerrit@cloudera.org>
To: impala-cr@cloudera.com, reviews@impala.incubator.apache.org
CC: Michael Ho <kwho@cloudera.com>, Dan Hecht <dhecht@cloudera.com>
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Subject: =?UTF-8?Q?=5BImpala-ASF-CR=5D_IMPALA-4813=3A_Round_on_divide_and_multiply=0A?=
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archived-at: Thu, 02 Mar 2017 00:11:57 -0000

Zach Amsden has uploaded a new patch set (#11).

Change subject: IMPALA-4813: Round on divide and multiply
......................................................................

IMPALA-4813: Round on divide and multiply

Address rounding on divide and multiply when results are truncated.

Testing: Manually ran some divides that should overflow, then added
the results to the test.  Made the decimal-test use rounding behavior
by default, and now the error margin of the test has decreased.

Initial perf results:

Multiply is totall uninteresting so far, all implementations
return the same values in the same time:

+-------------------------+-----------------------------------+
| sum(l_quantity * l_tax) | sum(l_extendedprice * l_discount) |
+-------------------------+-----------------------------------+
| 61202493.3700           | 114698450836.4234                 |
+-------------------------+-----------------------------------+
Fetched 1 row(s) in 1.13s

Divide shows no regression from prior with DECIMAL_V2 off:

+-----------------------------+-----------------------------------+
| sum(l_quantity / l_tax)     | sum(l_extendedprice / l_discount) |
+-----------------------------+-----------------------------------+
| 46178777464.523809516381723 | 61076151920731.010714279183910    |
+-----------------------------+-----------------------------------+
before:  Fetched 1 row(s) in 13.08s
after:   Fetched 1 row(s) in 13.06s

And with DECIMAL_V2 on:

+-----------------------------+-----------------------------------+
| sum(l_quantity / l_tax)     | sum(l_extendedprice / l_discount) |
+-----------------------------+-----------------------------------+
| 46178777464.523809523847285 | 61076151920731.010714285714202    |
+-----------------------------+-----------------------------------+
Fetched 1 row(s) in 16.06s

So the performance regression is not as bad as expected.  Still,
divide performance could use some work.

Change-Id: Ie6bfcbe37555b74598d409c6f84f06b0ae5c4312
---
M be/src/exprs/aggregate-functions-ir.cc
M be/src/exprs/decimal-operators-ir.cc
M be/src/exprs/expr-test.cc
M be/src/runtime/decimal-test.cc
M be/src/runtime/decimal-value.h
M be/src/runtime/decimal-value.inline.h
M be/src/runtime/types.cc
M be/src/runtime/types.h
M be/src/util/bit-util-test.cc
M be/src/util/bit-util.h
M be/src/util/string-parser.h
11 files changed, 849 insertions(+), 414 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/32/6132/11
-- 
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Ie6bfcbe37555b74598d409c6f84f06b0ae5c4312
Gerrit-PatchSet: 11
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Zach Amsden <zamsden@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dhecht@cloudera.com>
Gerrit-Reviewer: Michael Ho
Gerrit-Reviewer: Michael Ho <kwho@cloudera.com>
Gerrit-Reviewer: Zach Amsden <zamsden@cloudera.com>