Improvements in Database Metadata to prevent Statement leaks and enhance Statement caching

[cheenamalhotra]

This PR introduces below changes to SQLServerDatabaseMetadata:

• Improved Statement caching for different catalogs
• Enables Statement caching for 'null' catalog
• Enables closing un-cached Statements on completion of ResultSet (Prevents Statement Leaks)

[codecov-io]

Codecov Report

Merging #806 into dev will decrease coverage by <.01%.
The diff coverage is 82.97%.

@@             Coverage Diff              @@
##                dev     #806      +/-   ##
============================================
- Coverage     48.58%   48.57%   -0.01%     
+ Complexity     2794     2791       -3     
============================================
  Files           116      116              
  Lines         27879    27890      +11     
  Branches       4651     4652       +1     
============================================
+ Hits          13545    13548       +3     
- Misses        12124    12141      +17     
+ Partials       2210     2201       -9

Flag	Coverage Δ	Complexity Δ
#JDBC42	48.12% <82.97%> (+0.13%)	2750 <0> (+4)	⬆️
#JDBC43	48.49% <82.97%> (-0.06%)	2786 <0> (-7)

Impacted Files	Coverage Δ	Complexity Δ
...om/microsoft/sqlserver/jdbc/SQLServerBulkCopy.java	52.79% <69.23%> (+0.33%)	264 <0> (+1)	⬆️
...soft/sqlserver/jdbc/SQLServerDatabaseMetaData.java	34.91% <88.23%> (+1.42%)	66 <0> (+3)	⬆️
...rc/main/java/com/microsoft/sqlserver/jdbc/DDC.java	44.2% <0%> (-1.54%)	106% <0%> (-2%)
...ncurrentlinkedhashmap/ConcurrentLinkedHashMap.java	38.14% <0%> (-0.87%)	42% <0%> (-1%)
...m/microsoft/sqlserver/jdbc/SQLServerResultSet.java	32.38% <0%> (-0.39%)	252% <0%> (-4%)
...rc/main/java/com/microsoft/sqlserver/jdbc/dtv.java	62.28% <0%> (-0.18%)	0% <0%> (ø)
...in/java/com/microsoft/sqlserver/jdbc/IOBuffer.java	56.35% <0%> (+0.13%)	0% <0%> (ø)	⬇️
...n/java/com/microsoft/sqlserver/jdbc/Parameter.java	63.72% <0%> (+0.2%)	64% <0%> (ø)	⬇️
...om/microsoft/sqlserver/jdbc/ReaderInputStream.java	45.05% <0%> (+1.09%)	15% <0%> (ø)	⬇️

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[cheenamalhotra]

Jars for testing : mssql-jdbc-PR806.zip

[ulvii]

This is less readable to me. Maybe you could only "if else" the query string?

[cheenamalhotra]

Then we can't place it in try with resources block. Also will need another try block, and finally block to manually close it.
I don't see any issues - its a simple ternary operator.

[ulvii]

Suggested change

	+ "object_id=OBJECT_ID('" + Util.escapeSingleQuotes(destinationTableName) + "') "
	/**
	* Returns the column metadata for the destination table (and saves it for later)
	*/
	private void getDestinationMetadata() throws SQLServerException {
	if (null == destinationTableName) {
	SQLServerException.makeFromDriverError(null, null,
	SQLServerException.getErrString("R_invalidDestinationTable"), null, false);
	}
	SQLServerResultSet rs = null;
	SQLServerStatement stmt = null;
	String metaDataQuery = null;
	String bulkCopyEncrytionType = null;
	String escapedTableName = Util.escapeSingleQuotes(destinationTableName);
	try {
	if (null != destinationTableMetadata) {
	rs = (SQLServerResultSet) destinationTableMetadata;
	} else {
	stmt = (SQLServerStatement) connection.createStatement(ResultSet.TYPE_FORWARD_ONLY,
	ResultSet.CONCUR_READ_ONLY, connection.getHoldability(), stmtColumnEncriptionSetting);
	// Get destination metadata
	rs = stmt.executeQueryInternal(
	"sp_executesql N'SET FMTONLY ON SELECT * FROM " + escapedTableName + " '");
	}
	destColumnCount = rs.getMetaData().getColumnCount();
	destColumnMetadata = new HashMap<>();
	destCekTable = rs.getCekTable();
	if (connection.getServerSupportsColumnEncryption()) {
	metaDataQuery = "select collation_name, encryption_type from sys.columns where "
	+ "object_id=OBJECT_ID('" + escapedTableName + "') " + "order by column_id ASC";
	} else {
	metaDataQuery = "select collation_name from sys.columns where " + "object_id=OBJECT_ID('"
	+ escapedTableName + "') " + "order by column_id ASC";
	}
	try (SQLServerStatement statementMoreMetadata = (SQLServerStatement) connection.createStatement();
	SQLServerResultSet rsMoreMetaData = statementMoreMetadata.executeQueryInternal(metaDataQuery)) {
	for (int i = 1; i <= destColumnCount; ++i) {
	if (rsMoreMetaData.next()) {
	if (connection.getServerSupportsColumnEncryption()) {
	bulkCopyEncrytionType = rsMoreMetaData.getString("encryption_type");
	}
	destColumnMetadata.put(i, new BulkColumnMetaData(rs.getColumn(i), bulkCopyEncrytionType, null));
	} else {
	destColumnMetadata.put(i, new BulkColumnMetaData(rs.getColumn(i)));
	}
	}
	}
	} catch (SQLException e) {
	// Unable to retrieve metadata for destination
	throw new SQLServerException(SQLServerException.getErrString("R_unableRetrieveColMeta"), e);
	} finally {
	if (null != rs)
	rs.close();
	if (null != stmt)
	stmt.close();
	}
	}

[ulvii]

Please consider the suggestion above.