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ASF GitHub Bot commented on DRILL-4834: --------------------------------------- Github user daveoshinsky commented on a diff in the pull request: https://github.com/apache/drill/pull/570#discussion_r160777281 --- Diff: exec/java-exec/src/main/codegen/templates/Decimal/CastIntDecimal.java --- @@ -68,15 +68,31 @@ public void setup() { public void eval() { out.scale = (int) scale.value; + + <#if !type.to.endsWith("VarDecimal")> out.precision = (int) precision.value; + </#if> - <#if type.to == "Decimal9" || type.to == "Decimal18"> + <#if type.to.endsWith("VarDecimal")> + out.start = 0; + out.buffer = buffer; + String s = Long.toString((long)in.value); + for (int i = 0; i < out.scale; ++i) { // add 0's to get unscaled integer + s += "0"; --- End diff -- Agreed > decimal implementation is vulnerable to overflow errors, and extremely complex > ------------------------------------------------------------------------------ > > Key: DRILL-4834 > URL: https://issues.apache.org/jira/browse/DRILL-4834 > Project: Apache Drill > Issue Type: Bug > Components: Execution - Data Types > Affects Versions: 1.6.0 > Environment: Drill 1.7 on any platform > Reporter: Dave Oshinsky > Fix For: Future > > > While working on a fix for DRILL-4704, logic was added to CastIntDecimal.java > template to handle the situation where a precision is not supplied (i.e., the > supplied precision is zero) for an integer value that is to be casted to a > decimal. The Drill decimal implementation uses a limited selection of fixed > decimal precision data types (the total number of decimal digits, i.e., > Decimal9, 18, 28, 38) to represent decimal values. If the destination > precision is too small to represent the input integer that is being casted, > there is no clean way to deal with the overflow error properly. > While using fixed decimal precisions as is being done currently can lead to > more efficient use of memory, it often will actually lead to less efficient > use of memory (when the fixed precision is specified significantly larger > than is actually needed to represent the numbers), and it results in a > tremendous mushrooming of the complexity of the code. For each fixed > precision (and there are only a limited set of selections, 9, 18, 28, 38, > which itself leads to memory inefficiency), there is a separate set of code > generated from templates. For each pairwise combination of decimal or > non-decimal numeric types, there are multiple places in the code where > conversions must be handled, or conditions must be included to handle the > difference in precision between the two types. A one-size-fits-all approach > (using a variable width vector to represent any decimal precision) would > usually be more memory-efficient (since precisions are often over-specified), > and would greatly simplify the code. > Also see the DRILL-4184 issue, which is related. -- This message was sent by Atlassian JIRA (v6.4.14#64029)