Oracle CLOB performance

before :

we use null and  assign string value to CLOB object directly. but it will enter the performance issue to print the content in the loop:

 v_clob_xml_body         CLOB := NULL;

v_clob_xml_body := '123344444...............'

 

Performance tunning

after :

v_clob_xml_body         CLOB := empty_clob();

dbms_lob.createtemporary(v_clob_xml_body, true, 1024);  --Initialize the clob

 -- Open workbook
      dbms_lob.append(v_clob_xml_body,
         '<?xml version="1.0" encoding="ISO-8859-9"?>' || chr(10) ||
         '<?mso-application progid="Excel.Sheet"?>'|| chr(10) ||
         '<Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet"'||chr(10) ||
         ' xmlns:o="urn:schemas-microsoft-com:office:office"' || chr(10) ||
         ' xmlns:x="urn:schemas-microsoft-com:office:excel"' || chr(10) ||
         ' xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet"' || chr(10) ||
         ' xmlns:html="http://www.w3.org/TR/REC-html40">' || chr(10)
      );
      -- Set document properties
      dbms_lob.append(v_clob_xml_body,
         ' <DocumentProperties xmlns="urn:schemas-microsoft-com:office:office">' || chr(10) ||
         '  <Author>Sunil Sahasrabudhe</Author>' || chr(10) ||
         '  <LastAuthor>Emerson Process Management</LastAuthor>' || chr(10) ||
         '  <Created>'||TO_CHAR(SYSDATE, 'YYYY-MM-DD"T"HH24:MI:SS"Z"')||'</Created>' || chr(10) ||
         '  <LastSaved>'||TO_CHAR(SYSDATE, 'YYYY-MM-DD"T"HH24:MI:SS"Z"')||'</LastSaved>' || chr(10) ||
         '  <Company>Emerson Process Management</Company>' || chr(10) ||
         '  <Version>14.00</Version>' || chr(10) ||
         '</DocumentProperties>' || chr(10)
      );
      -- Set office document settings
      dbms_lob.append(v_clob_xml_body,
         ' <OfficeDocumentSettings xmlns="urn:schemas-microsoft-com:office:office">' || chr(10) ||
         '  <AllowPNG/>' || chr(10) ||
         ' </OfficeDocumentSettings>' || chr(10)
      );
      -- Start excel workbook
      dbms_lob.append(v_clob_xml_body,
         ' <ExcelWorkbook xmlns="urn:schemas-microsoft-com:office:excel">' || chr(10) ||
         '  <WindowHeight>8445</WindowHeight>' || chr(10) ||
         '  <WindowWidth>15030</WindowWidth>' || chr(10) ||
         '  <WindowTopX>120</WindowTopX>' || chr(10) ||
         '  <WindowTopY>45</WindowTopY>' || chr(10) ||
         '  <ProtectStructure>False</ProtectStructure>' || chr(10) ||
         '  <ProtectWindows>False</ProtectWindows>' || chr(10) ||
         ' </ExcelWorkbook>' || chr(10)
      );
      -- Define styles
      dbms_lob.append(v_clob_xml_body,
         ' <Styles>' || chr(10) ||
         '  <Style ss:ID="Default" ss:Name="Normal">' || chr(10) ||
         '   <Alignment ss:Vertical="Bottom"/>' || chr(10) ||
         '   <Borders/>' || chr(10) ||
         '   <Font ss:FontName="Arial" ss:Size="8"/>' || chr(10) ||
         '   <Interior/>' || chr(10) ||
         '   <NumberFormat/>' || chr(10) ||
         '   <Protection/>' || chr(10) ||
         '  </Style>' || chr(10) ||
         '  <Style ss:ID="s62">' || chr(10) ||
         '   <Borders>' || chr(10) ||
         '    <Border ss:Position="Bottom" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Left" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Right" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Top" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '   </Borders>' || chr(10) ||
         '   <Font ss:FontName="Arial" x:Family="Swiss" ss:Size="8" ss:Bold="1"/>' || chr(10) ||
         '   <Interior ss:Color="#D9D9D9" ss:Pattern="Solid"/>' || chr(10) ||
         '  </Style>' || chr(10) ||
         '  <Style ss:ID="s63">' || chr(10) ||
         '   <Borders>' || chr(10) ||
         '    <Border ss:Position="Bottom" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Left" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Right" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Top" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '   </Borders>' || chr(10) ||
         '   <Font ss:FontName="Arial" x:Family="Swiss" ss:Size="8"/>' || chr(10) ||
         '  </Style>' || chr(10) ||
         '  <Style ss:ID="s64">' || chr(10) ||
         '   <Borders>' || chr(10) ||
         '    <Border ss:Position="Bottom" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Left" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Right" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '    <Border ss:Position="Top" ss:LineStyle="Continuous" ss:Weight="1"/>' || chr(10) ||
         '   </Borders>' || chr(10) ||
         '  </Style>' || chr(10) ||
         ' </Styles>' || chr(10)
      );
      -- Start of Item Sync Report sheet
      dbms_lob.append(v_clob_xml_body,
         ' <Worksheet ss:Name="Item Sync Report">' || chr(10) ||
         '  <Table ss:ExpandedColumnCount="6" ss:ExpandedRowCount="'||
             v_num_exp_rowcount||'" x:FullColumns="1"' || chr(10) ||
         --'   x:FullRows="1" ss:DefaultColumnWidth="42" ss:DefaultRowHeight="11.25">' || chr(10) ||
         '   x:FullRows="1" ss:DefaultColumnWidth="42" ss:AutoFitRowHeight="1">' || chr(10) ||
         '   <Column ss:Width="108.75"/>' || chr(10) ||
         '   <Column ss:Width="74.25"/>' || chr(10) ||
         '   <Column ss:Width="69"/>' || chr(10) ||
         '   <Column ss:Width="96"/>' || chr(10) ||
         '   <Column ss:Width="72"/>' || chr(10) ||
         '   <Column ss:Width="186"/>' || chr(10) ||
         '   <Row>' || chr(10) ||
         '    <Cell><Data ss:Type="String">Item Synchronization Report</Data></Cell>' || chr(10) ||
         '   </Row>' || chr(10) ||
         '   <Row>' || chr(10) ||
         '    <Cell><Data ss:Type="String">Date: '||to_char(SYSDATE, 'DD-MON-YYYY')||'</Data></Cell>' || chr(10) ||
         '   </Row>' || chr(10)
      );
      -- Write table header
      dbms_lob.append(v_clob_xml_body,
         '   <Row ss:Index="4">' || chr(10) ||
         '    <Cell ss:StyleID="s62"><Data ss:Type="String">Item</Data></Cell>' || chr(10) ||
         '    <Cell ss:StyleID="s62"><Data ss:Type="String">Item Description</Data></Cell>' || chr(10) ||
         '    <Cell ss:StyleID="s62"><Data ss:Type="String">User Item Type</Data></Cell>' || chr(10) ||
         '    <Cell ss:StyleID="s62"><Data ss:Type="String">Item Catalog Group ID</Data></Cell>' || chr(10) ||
         '    <Cell ss:StyleID="s62"><Data ss:Type="String">VLS Item Status</Data></Cell>' || chr(10) ||
         '    <Cell ss:StyleID="s62"><Data ss:Type="String">Message</Data></Cell>' || chr(10) ||
         '   </Row>' || chr(10)
      );

dbms_lob.append(v_clob_xml_body,
            '   <Row>' || chr(10) ||
            '    <Cell ss:StyleID="s63"><Data ss:Type="String">'||
               tab_item_sync_rpt(v_chr_index).item_name||'</Data></Cell>' || chr(10) ||
            '    <Cell ss:StyleID="s63"><Data ss:Type="String">'||
               tab_item_sync_rpt(v_chr_index).item_description||'</Data></Cell>' || chr(10) ||
            '    <Cell ss:StyleID="s63"><Data ss:Type="String">'||
               tab_item_sync_rpt(v_chr_index).user_item_type||'</Data></Cell>' || chr(10) ||
            '    <Cell ss:StyleID="s64"><Data ss:Type="String">'||
               to_char(tab_item_sync_rpt(v_chr_index).item_catalog_group_id)||'</Data></Cell>'|| chr(10)||
            '    <Cell ss:StyleID="s63"><Data ss:Type="String">'||
               tab_item_sync_rpt(v_chr_index).item_status||'</Data></Cell>' || chr(10) ||
            '    <Cell ss:StyleID="s63"><Data ss:Type="String">'||
               replace(tab_item_sync_rpt(v_chr_index).message,chr(10),'&#10;')||'</Data></Cell>' || chr(10) ||
            '   </Row>' || chr(10)
         );

-- Close workbook      dbms_lob.append(v_clob_xml_body,         '  </Table>' || chr(10) ||         '  <WorksheetOptions xmlns="urn:schemas-microsoft-com:office:excel">' || chr(10) ||         '   <Print>' || chr(10) ||         '    <ValidPrinterInfo/>' || chr(10) ||         '    <HorizontalResolution>600</HorizontalResolution>' || chr(10) ||         '    <VerticalResolution>600</VerticalResolution>' || chr(10) ||         '   </Print>' || chr(10) ||         '   <Selected/>' || chr(10) ||         '   <Panes>' || chr(10) ||         '    <Pane>' || chr(10) ||         '     <Number>3</Number>' || chr(10) ||         '     <ActiveRow>12</ActiveRow>' || chr(10) ||         '    </Pane>' || chr(10) ||         '   </Panes>' || chr(10) ||         '   <ProtectObjects>False</ProtectObjects>' || chr(10) ||         '   <ProtectScenarios>False</ProtectScenarios>' || chr(10) ||         '  </WorksheetOptions>' || chr(10) ||         ' </Worksheet>' || chr(10) ||         '</Workbook>' || chr(10)      );