Copying Table Content to CLOB variable

Question

I have a process that generates two million records into a temporary table (forecasted to increase to 9 million).The data from the temporary table should then be copied into a CLOB and stored back into a database column.

At present I am facing performance issues with copying the data from the temporary table into a CLOB column which takes 12mins . Code snippet is given below.

Is there any better way of doing this ?

Code Snippet

DECLARE
  lv_clob_temp  CLOB;
  lv_content_file REPORT_DETAILS.content_file%type;
  lv_rev_header_file REPORT_DETAILS.rev_header_file%type;
  lv_rev_content_file REPORT_DETAILS.rev_content_file%type;
  type rec_report_temp is table of REPORT_TEMP%ROWTYPE;
  tbl_report_temp rec_report_temp;
  lv_bulk_limit pls_integer := 100000;
BEGIN

  -- fetch master data for the report
  SELECT
    content_file
    , rev_content_file
  INTO
    lv_content_file
    , lv_rev_content_file


  FROM   REPORT_DETAILS
  WHERE  rep_id = 1 for update;

dbms_lob.createtemporary(lv_clob_temp, TRUE, DBMS_LOB.SESSION );

--Data for the content extract
  open cur_rec for 'SELECT COL1, COL2, COL3, COL4, COL5, COL6, COL7 from REPORT_TEMP';

  loop
  FETCH cur_rec BULK COLLECT INTO tbl_report_temp LIMIT lv_bulk_limit;
  EXIT WHEN tbl_report_temp.count = 0;

  for i in 1..tbl_report_temp.count
  loop
  lv_clob_temp :=  tbl_report_temp(i).COL1
  ||','||tbl_report_temp(i).COL2
  ||','||to_char(tbl_report_temp(i).COL3,'DD/MM/YYYY')
  ||','||to_char(tbl_report_temp(i).SPAD,'DD/MM/YYYY')
  ||','||to_char(tbl_report_temp(i).COL5,'DD/MM/YYYY')
  ||','||tbl_report_temp(i).COL7
  ||','||to_char(tbl_report_temp(i).COL6,'DD/MM/YYYY')
  || lv_crlf;

  DBMS_LOB.APPEND(lv_content_file, lv_clob_temp);

  lv_clob_temp :=  tbl_report_temp(i).COL1
  ||','||tbl_report_temp(i).COL2
  ||','||to_char(tbl_report_temp(i).COL3,'DD/MM/YYYY')
  ||','||to_char(tbl_report_temp(i).SPAD,'DD/MM/YYYY')
  ||','||to_char(tbl_report_temp(i).COL5,'DD/MM/YYYY')
  || lv_crlf;

  DBMS_LOB.APPEND(lv_rev_content_file, lv_clob_temp);


  end loop;

  end loop;

  UPDATE REPORT_DETAILS
  set content_file = lv_content_file
    , rev_content_file = lv_rev_content_file
  WHERE  rep_id = 1;

  COMMIt;

END;

Answer 1

My friend suggested me to use the below-given script,

To achieve CLOB concatenation use the function stragg_clob (run the below script).

    create or replace type rmd_agg_type as object
    (
      total clob,

      static function
       ODCIAggregateInitialize(sctx IN OUT rmd_agg_type )
      return number,

      member function
       ODCIAggregateIterate(self IN OUT rmd_agg_type ,value IN varchar2 )
      return number,

      member function
       ODCIAggregateTerminate(self IN rmd_agg_type, returnValue OUT  clob,  flags IN number)
      return number,

      member function
       ODCIAggregateMerge(self IN OUT rmd_agg_type, ctx2 IN rmd_agg_type)
      return number
    );
    /

    create or replace type body rmd_agg_type
    is

      static function ODCIAggregateInitialize(sctx IN OUT rmd_agg_type)
      return number
      is
      begin
        sctx := rmd_agg_type( null );
        return ODCIConst.Success;
      end;

      member function ODCIAggregateIterate(self IN OUT rmd_agg_type,
                                           value IN varchar2 )
      return number
      is
      begin
        self.total := self.total || ',' || value;
        return ODCIConst.Success;
      end;

      member function ODCIAggregateTerminate(self IN rmd_agg_type,
                                            returnValue OUT clob,
                                            flags IN number)
      return number
      is
      begin
        returnValue := ltrim(self.total,',');
        return ODCIConst.Success;
      end;

      member function ODCIAggregateMerge(self IN OUT rmd_agg_type,
                                        ctx2 IN rmd_agg_type)
      return number
      is
      begin
        self.total := self.total || ctx2.total;
        return ODCIConst.Success;
      end;

    end;
    /

    CREATE or replace
    FUNCTION stragg_clob(input varchar2 )
    RETURN clob
    PARALLEL_ENABLE AGGREGATE USING rmd_agg_type;
    /

    grant execute on stragg_clob to user_schema;


    To mimic your scenario I created two table and used it below-populated 2million records and then update the destination table CLOB column by appending values.


    create table seed_values (name1 varchar2(10), col2 varchar2(250));

    insert into seed_values
    select 'TMP'||level, 'ADI'||level from dual connect by level<2000000;

    commit;

    create table clob_value (base_data clob);

    insert into clob_value values ('Value from before seed data#');

    commit;
    update clob_value set base_data = base_data || (
                                                     select sys.stragg_clob(name1||','||col2) as enames from seed_values
                                                     );