Sergio Peña created HIVE-11611:
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Summary: A bad performance regression issue with Parquet happens
if Hive does not select any columns
Key: HIVE-11611
URL: https://issues.apache.org/jira/browse/HIVE-11611
Project: Hive
Issue Type: Sub-task
Affects Versions: 2.0.0
Reporter: Sergio Peña
Assignee: Ferdinand Xu
A possible performance issue may happen with the below code when using a query
like this {{SELECT count(1) FROM parquetTable}}.
{code}
if (!ColumnProjectionUtils.isReadAllColumns(configuration) &&
!indexColumnsWanted.isEmpty()) {
MessageType requestedSchemaByUser =
getSchemaByIndex(tableSchema, columnNamesList, indexColumnsWanted);
return new ReadContext(requestedSchemaByUser, contextMetadata);
} else {
return new ReadContext(tableSchema, contextMetadata);
}
{code}
If there are not columns nor indexes selected, then the above code will read
the full schema from Parquet even if Hive does not do anything with such values.
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