Taras Bobrovytsky has uploaded a new patch set (#4).
Change subject: IMPALA-4939, IMPALA-4939: Decimal V2 multiplication
......................................................................
IMPALA-4939, IMPALA-4939: Decimal V2 multiplication
Implement the new DECIMAL return type rules for multiply expressions,
active when query option DECIMAL_V2=1. The algorithm for determining
the type of the result of multiplication is described in the JIRA.
DECIMAL V1:
+-----------------------------------------------------------------------+
| typeof(cast('0.1' as decimal(38,38)) * cast('0.1' as decimal(38,38))) |
+-----------------------------------------------------------------------+
| DECIMAL(38,38) |
+-----------------------------------------------------------------------+
+-----------------------------------------------------------------------+
| typeof(cast('0.1' as decimal(38,15)) * cast('0.1' as decimal(38,15))) |
+-----------------------------------------------------------------------+
| DECIMAL(38,30) |
+-----------------------------------------------------------------------+
DECIMAL V2:
+-----------------------------------------------------------------------+
| typeof(cast('0.1' as decimal(38,38)) * cast('0.1' as decimal(38,38))) |
+-----------------------------------------------------------------------+
| DECIMAL(38,37) |
+-----------------------------------------------------------------------+
+-----------------------------------------------------------------------+
| typeof(cast('0.1' as decimal(38,15)) * cast('0.1' as decimal(38,15))) |
+-----------------------------------------------------------------------+
| DECIMAL(38,6) |
+-----------------------------------------------------------------------+
In this patch, we also fix the early multiplication overflow. We compute
an int256 intermediate value, which we then attempt to scale down and
round to int128.
Benchmarks:
Query:
select
sum(l_quantity * l_tax) +
sum(l_extendedprice * l_discount)
from lineitem_big;
Before:
DECIMAL_V2 disabled: 6.68s
DECIMAL_V2 enabled : 6.77s
After:
DECIMAL_V2 disabled: 6.66s
DECIMAL_V2 enabled : 6.58s
In the above benchmark, we are selecting from lineitem_big, which has
about 100 times as many rows as the normal lineitem.
Query:
select
sum(l_quantity * l_tax * cast(1 as decimal(38, 37))) +
sum(l_extendedprice * l_discount * cast(1 as decimal(38, 37)))
from lineitem
Before:
DECIMAL_V2 disabled: 0.23s
DECIMAL_V2 enabled : 0.45s
After:
DECIMAL_V2 disabled: 2.65s
DECIMAL_V2 enabled : 2.54s
The query is slower after the patch because the intermediate result is
int256.
Change-Id: I37ad6232d7953bd75c18dc86e665b2b501a1ebe1
---
M be/src/exprs/expr-test.cc
M be/src/runtime/decimal-value.inline.h
M be/src/util/bit-util.h
M fe/src/main/java/org/apache/impala/analysis/TypesUtil.java
4 files changed, 253 insertions(+), 58 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/38/7438/4
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I37ad6232d7953bd75c18dc86e665b2b501a1ebe1
Gerrit-PatchSet: 4
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Taras Bobrovytsky <[email protected]>
Gerrit-Reviewer: Dan Hecht <[email protected]>
Gerrit-Reviewer: Michael Ho <[email protected]>
Gerrit-Reviewer: Taras Bobrovytsky <[email protected]>
Gerrit-Reviewer: Tim Armstrong <[email protected]>
Gerrit-Reviewer: Zach Amsden <[email protected]>
