Top N biggest tables (with lobs, indexes and nested table)

with 
  seg as (
     select 
       owner,segment_name
      ,segment_type
      ,tablespace_name
      ,sum(blocks) blocks
      ,sum(bytes)  bytes
     from dba_segments s
     where  segment_type not in (
       'TYPE2 UNDO'
      ,'ROLLBACK'
      ,'SYSTEM STATISTICS'
     )
     and segment_name not like 'BIN$%' --not in recyclebin
     group by owner,segment_name,segment_type,tablespace_name
  )
 ,segs as (
     select 
       owner,segment_name
      ,case when segment_name like 'DR$%$%' then 'CTX INDEX' else segment_type end segment_type
      ,tablespace_name
      ,case 
         when segment_name like 'DR$%$%' 
           then (select table_owner||'.'||table_name from dba_indexes i where i.owner=s.owner and i.index_name  (more...)

“Collection iterator pickler fetch”: pipelined vs simple table functions

Alex R recently discovered interesting thing: in SQL pipelined functions work much faster than simple non-pipelined table functions, so if you already have simple non-pipelined table function and want to get its results in sql (select * from table(fff)), it’s much better to create another pipelined function which will get and return its results through PIPE ROW().

A bit more details:

Assume we need to return collection “RESULT” from PL/SQL function into SQL query “select (more...)

SQL*Plus tips #8: How to read the output of dbms_output without “serveroutput on”

When “serveroutput” is enabled, SQL*Plus executes “BEGIN DBMS_OUTPUT.GET_LINES(:LINES, :NUMLINES); END;” after each command.
That’s why I don’t like when it is always enabled: it adds extra calls and round-trips and it is inconvenient when I want to get a plan of the last executed query:

SQL> set serverout on;
SQL> select * from dual;

D
-
X

SQL> select * from table(dbms_xplan.display_cursor('','','allstats last'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------
SQL_ID  9babjv8yq8ru3, child number 0

BEGIN  (more...)

Bug with integer literals in PL/SQL

This interesting question was posted on our russian forum yesterday:

We have a huge PL/SQL package and this simple function returns wrong result when it’s located at the end of package body:

create or replace package body PKGXXX as
  ...
  function ffff return number is
  nRes number;
  begin        
    nRes :=  268435456;
    return nRes;
  end;
end;
/

But it works fine in any of the following cases:
* replace 268435456 with power(2, 28), or
* replace (more...)

Oracle issues after upgrade to 12.2

Sometimes it’s really hard even to create reproducible test case to send it to oracle support, especially in case of intermittent errors.
In such cases, I think it would be really great to have access to similar service requests or bugs of other oracle clients.
So while my poll about knowledge sharing is still active, I want to share a couple of bugs we have faced after upgrade to 12.2 (and one bug from (more...)

Triggers and Redo: changes on 12.2

In one of the previous posts I showed How even empty trigger increases redo generation, but running the test from that post, I have found that this behaviour a bit changed on 12.2:
In my old test case, values of column A were equal to values of B, and on previous oracle versions including 12.1.0.2 we can see that even though “update … set B=A” doesn’t change really “B”, even (more...)

Adaptive serial direct path read decision ignores object statistics since 12.1

On versions 11.2.0.2 – 11.2.0.4 Oracle uses objects’ statistics to make direct path reads decision (of course, if “_direct_read_decision_statistics_driven” haven’t changed it to “false”), and we can force serial direct reads on statement level using sql profiles with hints INDEX_STATS/TABLES_STATS, but since at least 12.1.0.2 this decision ignores statistics.

Btw, thanks to Jure Bratina, we know now, that we need to repeat hint TABLE_STATS at (more...)

Easy(lazy) way to check which programs have properly configured FetchSize

select 
   s.module
  ,ceil(max(s.rows_processed/s.fetches)) rows_per_fetch
from v$sql s
where 
    s.rows_processed>100
and s.executions    >1
and s.fetches       >1
and s.module is not null
and s.command_type  = 3    -- SELECTs only
and s.program_id    = 0    -- do not account recursive queries from stored procs
and s.parsing_schema_id!=0 -- <> SYS
group by s.module
order by rows_per_fetch desc nulls last
/

PL/SQL functions: Iterate and keys for associative arrays

Unfortunately associative arrays still require more “coding”:
we still can’t use “indices of” or “values of” in simple FOR(though they are available for FORALL for a long time), don’t have convinient iterators and even function to get all keys…
That’s why I want to show my templates for such things like iterator and keys function. You can adopt these functions and create them on schema level.

declare 
   type numbers  is table of number;
   type anumbers  (more...)

How to group connected elements (or pairs)

I see quite often when developers ask questions about connected components:

Table “MESSAGES” contains fields “SENDER” and “RECIPIENT”, which store clients id.
How to quickly get all groups of clients who are connected even through other clients if the table has X million rows?
So for this table, there should be 4 groups:
  • (1, 2, 4, 8, 16)
  • (3, 6, 12)
  • (5, 10, 20)
  • (7, 14)
  • (9, 18)
SENDERRECIPIENT
12
24
3 (more...)