[jira] [Commented] (KYLIN-3398) Inaccurate arithmetic operation in LookupTableToHFileJob#calculateShardNum

["jiatao.tao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KYLIN-3398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16504428#comment-16504428 ] 

jiatao.tao commented on KYLIN-3398:
-----------------------------------

Thanks a lot! I'll take a look.

> Inaccurate arithmetic operation in LookupTableToHFileJob#calculateShardNum
> --------------------------------------------------------------------------
>
>                 Key: KYLIN-3398
>                 URL: https://issues.apache.org/jira/browse/KYLIN-3398
>             Project: Kylin
>          Issue Type: Bug
>            Reporter: Ted Yu
>            Assignee: jiatao.tao
>            Priority: Major
>
> There're two issues with the following code:
> {code}
>     private int calculateShardNum(KylinConfig kylinConfig, long dataSize) {
>         long shardSize = kylinConfig.getExtTableSnapshotShardingMB() * 1024 * 1024;
>         return dataSize < shardSize ? 1 : (int) (Math.ceil(dataSize / shardSize));
> {code}
> getExtTableSnapshotShardingMB returns an int. The multiplication is done using 32-bit arithmetic, and then used in a context that expects an expression of type "long".
> Second, Math.ceil expects a double. The integer division would lose some precision.



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