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https://issues.apache.org/jira/browse/HIVE-15530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15812396#comment-15812396
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Chaoyu Tang commented on HIVE-15530:
------------------------------------
[~Yibing] The patch looks good. However, I have a small question about this:
{code}
static boolean columnsIncluded(List<FieldSchema> oldCols, List<FieldSchema>
newCols) {
if (oldCols.size() > newCols.size()) {
return false;
} else if (oldCols.size() == newCols.size()){
return areSameColumns(oldCols, newCols);
} else {
return areSameColumns(oldCols, newCols.subList(0, oldCols.size()));
}
}
{code}
For the alter table only changing the column name or/and position in a table,
the oldCols.size() equals to newCols.size(), but areSameColumns(oldCols,
newCols) might return false, in this case, should we still update the the
column statistics?
> Optimize the column stats update logic in table alteration
> ----------------------------------------------------------
>
> Key: HIVE-15530
> URL: https://issues.apache.org/jira/browse/HIVE-15530
> Project: Hive
> Issue Type: Bug
> Components: Hive
> Reporter: Yibing Shi
> Assignee: Yibing Shi
> Attachments: HIVE-15530.1.patch, HIVE-15530.2.patch,
> HIVE-15530.3.patch, HIVE-15530.4.patch
>
>
> Currently when a table is altered, if any of below conditions is true, HMS
> would try to update column statistics for the table:
> # database name is changed
> # table name is changed
> # old columns and new columns are not the same
> As a result, when a column is added to a table, Hive also tries to update
> column statistics, which is not necessary. We can loose the last condition by
> checking whether all existing columns are changed or not. If not, we don't
> have to update stats info.
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