/**
* Returns a list of the columns making up a table. The argument is a serialized
* TDescribeTableParams object. The return type is a serialised TDescribeTableResult object.
*
* @see Frontend#describeTable
*/
public byte[] describeTable(byte[] thriftDescribeTableParams) throws ImpalaException {
TDescribeTableParams params = new TDescribeTableParams();
deserializeThrift(params, thriftDescribeTableParams);
TDescribeTableResult result = new TDescribeTableResult();
result.setColumns(frontend.describeTable(params.getDb(), params.getTable_name()));
TSerializer serializer = new TSerializer(protocolFactory);
try {
return serializer.serialize(result);
} catch (TException e) {
throw new InternalException(e.getMessage());
}
}
/*
* Builds results for a DESCRIBE <table> command. This consists of the column
* definition for each column in the table.
*/
private static TDescribeTableResult describeTableMinimal(Table table) {
TDescribeTableResult descResult = new TDescribeTableResult();
descResult.results = Lists.newArrayList();
// Get description of all the table's columns (includes partition columns).
for (Column column : table.getColumnsInHiveOrder()) {
TColumnValue colNameCol = new TColumnValue();
colNameCol.setString_val(column.getName());
TColumnValue dataTypeCol = new TColumnValue();
dataTypeCol.setString_val(column.getType().toString().toLowerCase());
TColumnValue commentCol = new TColumnValue();
commentCol.setString_val(column.getComment() != null ? column.getComment() : "");
descResult.results.add(
new TResultRow(Lists.newArrayList(colNameCol, dataTypeCol, commentCol)));
}
return descResult;
}
/*
* Builds a TDescribeTableResult that contains the result of a DESCRIBE FORMATTED
* <table> command. For the formatted describe output the goal is to be exactly the
* same as what Hive (via HiveServer2) outputs, for compatibility reasons. To do this,
* Hive's MetadataFormatUtils class is used to build the results.
*/
private static TDescribeTableResult describeTableFormatted(Table table) {
TDescribeTableResult descResult = new TDescribeTableResult();
descResult.results = Lists.newArrayList();
org.apache.hadoop.hive.metastore.api.Table msTable = table.getMetaStoreTable().deepCopy();
// Fixup the metastore table so the output of DESCRIBE FORMATTED matches Hive's.
// This is to distinguish between empty comments and no comments (value is null).
for (FieldSchema fs : msTable.getSd().getCols())
fs.setComment(table.getColumn(fs.getName()).getComment());
for (FieldSchema fs : msTable.getPartitionKeys()) {
fs.setComment(table.getColumn(fs.getName()).getComment());
}
// To avoid initializing any of the SerDe classes in the metastore table Thrift
// struct, create the ql.metadata.Table object by calling the empty c'tor and
// then calling setTTable().
org.apache.hadoop.hive.ql.metadata.Table hiveTable =
new org.apache.hadoop.hive.ql.metadata.Table();
hiveTable.setTTable(msTable);
StringBuilder sb = new StringBuilder();
// First add all the columns (includes partition columns).
sb.append(
MetaDataFormatUtils.getAllColumnsInformation(
msTable.getSd().getCols(), msTable.getPartitionKeys()));
// Add the extended table metadata information.
sb.append(MetaDataFormatUtils.getTableInformation(hiveTable));
for (String line : sb.toString().split("\n")) {
// To match Hive's HiveServer2 output, split each line into multiple column
// values based on the field delimiter.
String[] columns = line.split(MetaDataFormatUtils.FIELD_DELIM);
TResultRow resultRow = new TResultRow();
for (int i = 0; i < NUM_DESC_FORMATTED_RESULT_COLS; ++i) {
TColumnValue colVal = new TColumnValue();
colVal.setString_val(null);
if (columns.length > i) {
// Add the column value.
colVal.setString_val(columns[i]);
}
resultRow.addToColVals(colVal);
}
descResult.results.add(resultRow);
}
return descResult;
}