Encountering exception ORA-01555

Question

I was given a problem to solve , in which there is table called Scenarios in the Master Db which contains the details of all the Tablespace for which I have to find the size. The O/P should contain Table size(actually consumed) and index size and no of rows.

So, I wrote a sizing script(PL/SQL) to find the size of all the Table Space on that particular DB server.

But I am getting this particular exception after it runs for days.

ORA-01555: snapshot too old: rollback segment number 9 with name "_SYSSMU9$" too small

I am not sure what might be causing this, as the data size is not that huge.

I am attaching the Script

    SET SERVEROUTPUT ON size '10000000'
declare
TYPE cur_typ IS REF CURSOR;
a_Temp number := 0;
x_Total number := 0;
i number := 0;
c_cursor cur_typ;
query_str varchar2(500);
num_long Long;
currentScenarioDB nvarchar2(255);
tableExists number := 0;
scenarioId varchar2(50);
scenarioName varchar2(100);
dbIdentifier nvarchar2(50);
queryToFindScenarioNameAndId varchar2(400) := 'select scenarioId,name from scenarios where dbidentifier =  ';
selectQuery varchar2(400) := 'select scenarioId,name from scenarios where dbidentifier =  ';
insertStatement varchar2(2000) := 'Insert Into ScenarioTableAndIndexSize  values (:1,:2,:3,:4,:5,:6,:7) ';
-- scenarioId,scenarioname,,dbIdentifier,tablename,dataSize,IndexSize,rowNumber
tableIndexSize number := 0;
numOfRows number := 0;
rowNum number := 0;
tableDataSize number := 0;
Cursor getScenarioDb is select dbidentifier from scenarios where dbidentifier IN (select Distinct(TABLESPACE_NAME) from dba_tables);
begin
DBMS_OUTPUT.ENABLE(10000000);
execute immediate 'truncate table ScenarioTableAndIndexSize';
open getScenarioDb;
fetch getScenarioDb into currentScenarioDB;
while getScenarioDb%found
loop
queryToFindScenarioNameAndId := selectQuery || '''' || currentScenarioDB || '''';
execute immediate queryToFindScenarioNameAndId  into scenarioId,scenarioName;
              declare
              queryToFindNoofRows varchar2(1000);
        queryConstruct varchar2(32767) := '';
        outputTableInScenarioDb nvarchar2(256);
        Cursor getTablesInScenario is select DISTINCT TABLE_NAME from dba_tables where owner =  currentScenarioDB and TABLE_NAME not like 'BIN%' and table_name != 'SCENARIOTABLEANDINDEXSIZE' order by table_name;
        begin
              tableExists := 0;
        open getTablesInScenario;
        fetch getTablesInScenario into outputTableInScenarioDb;
        while getTablesInScenario%found
        loop
              queryConstruct  := 'select nvl( sum (';
              tableIndexSize  := 0;
              tableDataSize := 0;
              numOfRows := 0;
              queryToFindNoofRows := 'select count(*) from  '||  currentScenarioDB || '.' ||outputTableInScenarioDb;
              execute immediate queryToFindNoofRows into numOfRows;
              if numOfRows > 0 then
---------------------------Beginning Of Section to find Table data Size------------------------------------------------------------------------------------------------
                  declare
                      Cursor getColumnsInTables is select * from dba_tab_columns where Table_Name = outputTableInScenarioDb and owner = currentScenarioDB;
                      dbaTabColumnRow dba_tab_columns%rowtype;
                      dataType varchar2(40);
                      fields varchar2(1000);
                      begin
                      open getColumnsInTables;
                      fetch getColumnsInTables Into dbaTabColumnRow;
                      while getColumnsInTables%found
                      loop
                      dataType := dbaTabColumnRow.DATA_TYPE;
                     if dataType = 'CLOB' then
                        fields := 'nvl(DBMS_LOB.GETLENGTH(' || dbaTabColumnRow.COLUMN_NAME ||'),0)';
                     elsif dataType = 'BLOB' then
                        fields := 'nvl(DBMS_LOB.GETLENGTH('|| dbaTabColumnRow.COLUMN_NAME ||'),0)';
                     elsif dataType = 'LONG' then
                        fields := 'nvl(VSIZE(''''),0)';
                        x_Total := 0;
                        query_str := 'SELECT  ' || dbaTabColumnRow.COLUMN_NAME || '  FROM  ' || currentScenarioDB || '.' ||outputTableInScenarioDb;
                                      OPEN c_cursor FOR query_str;
                                  LOOP
                                  FETCH c_cursor INTO num_long;
                                  EXIT WHEN c_cursor%NOTFOUND;
                             a_Temp:=length(num_long);
                             x_Total:= x_Total + a_Temp;
                                  END LOOP;
                           CLOSE c_cursor;
                     else
                        fields := 'nvl(vsize(' || dbaTabColumnRow.COLUMN_NAME || '),0)';
                     end if;
                           fetch getColumnsInTables Into dbaTabColumnRow;
                         if getColumnsInTables%found then
                       queryConstruct := queryConstruct || fields||'+';
                     else
                     queryConstruct := queryConstruct || fields;
                     end if;
                      end loop;
                      end;
                                      queryConstruct := queryConstruct || '),0) as sizeOfTable from  ' || currentScenarioDB || '.' ||outputTableInScenarioDb;            
                                      --dbms_output.put_line(queryConstruct);
                                      execute immediate queryConstruct into tableDataSize;
---------------------------End Of Section to find Table data Size-------------------------------------------------------------------------------------------------------------

                      ---------------Section To find index size
                          declare
                Index_Name nvarchar2(4000);
                sql_statement varchar2(1000) := 'select nvl(USED_SPACE,0) from index_stats';
                stat1 varchar2(1000) := 'analyze index ';
                stat2 varchar2(1000) := '  validate structure';
                stat3 varchar2(2000) := '';
                size1 number := 0;
                cursor indexOnTable is select INDEX_NAME from dba_indexes where tablespace_name = currentScenarioDB and  table_name = outputTableInScenarioDb and index_type = 'NORMAL';
                    begin
                    open indexOnTable;
                    fetch indexOnTable into Index_Name;
                    while indexOnTable%found
                    loop
                      stat3 := stat1 || currentScenarioDB ||'.' ||Index_Name || stat2;
                      execute immediate stat3;
                      execute immediate  sql_statement into size1;
                      tableIndexSize := tableIndexSize + size1;
                    fetch indexOnTable into Index_Name;
                    end loop;
                    close indexOnTable;
            end;
                      -----end of section to find index size
              else
                rowNum := rowNum + 1;
              end if;
                            tableDataSize := x_Total + tableDataSize;
              execute immediate insertStatement using   scenarioId,scenarioName,currentScenarioDB,outputTableInScenarioDb,tableDataSize,tableIndexSize,numOfRows;
                               x_Total := 0;
              fetch getTablesInScenario into outputTableInScenarioDb;
        end loop;
        end;
fetch getScenarioDb into currentScenarioDB;
end loop;
close getScenarioDb;
end;

The size of the table is found out this way :

1. If the field is of type Lob then to calculate its size I use nvl(DBMS_LOB.GETLENGTH(),0)
2. If the field is of type Long then I loop over all the Long values and find their size
   using the built in Length() function
3. If the field is of any other Type I use nvl(vsize(),0) Just to specify the user has permissions on all the DBs

And then I sum all of them up to find the total Data size in the table.

Can some one tell me what I am doing wrong or What I should do to fix the error ?

Thanks.

Answer 1

Gaius is right, use DBA_TABLES for NUM_ROWS and DBA_SEGMENTS for size:

select owner,table_name,num_rows,last_analyzed from dba_tables;

The num_rows count is as of LAST_ANALYZED date, which should be close enough even without running DBMS_STATS.

For sizing:

select owner,segment_type,sum(bytes)/1024/1024 size_mb
from dba_segments
group by owner,segment_type;

or (depending what level of details you need):

select owner,segment_name,sum(bytes)/1024/1024 size_mb
from dba_segments
group by owner,segment_name;

For LOBs you'll need to join it to DBA_LOBS, for indexes to DBA_INDEXES, for tables to DBA_TABLES. A lot will depend on your specific requirement. Since you mentioned you are trying to figure out used space in tablespace it might be as simple as:

select sum(bytes)/1024/1024 size_mb
from dba_segments
where tablespace_name='YOUR_TBLSP_NAME';

Your solution would really work only with small DB as it would not be feasible to read all data on large DB.

I am hesitant to post how to address ORA-1555 as in this case this it NOT your primary issue but just for completeness - you are on 10g using automatic undo management so your DBA would have to increase undo_retention in your database (the ixora link is relevant to a DB without auto undo management).

Answer 2

Do an analyze (DBMS_STATS.GATHER_SCHEMA_STATS) and look in DBA_TABLES for NUM_ROWS. Look in DBA_SEGMENTS.BYTES to find the size of each object.

You are getting ORA-1555 because your logs have wrapped all the way 'round in that time.