Turning rows into columns

Penshaw Monument
Turning Moo’s into Columns?

It’s odd how some things pass you by in new Oracle releases. Today I discovered “sys.odcinumberlist” and “sys.odcivarchar2list“.

I was wanting to generate a pre-defined list for a join to ensure each value was represented, and came up with the new in Oracle 12 function “sys.odcinumberlist”, so not new! Well, there’s 2 straightforward functions: “sys.odcinumberlist” and “sys.odcivarchar2list”.

How are they used?

SELECT column_value AS number_list
FROM sys.odcinumberlist(1,2,5,7,9,5,2,-34,5,43,2,0)
ORDER BY number_list;

NUMBER_LIST
-----------
        -34
          0
          1
          2
          2
          2
          5
          5
          5
          7
          9
         43

12 rows selected.

Note how I have had to alias the "column value" virtual column to allow mne to sort the list
SELECT column_value AS char_list FROM sys.odcivarchar2list('A','V','DD');

CHAR_LIST
---------
A
V
DD

Nice, simple, with a limit of 32768 items in the list. So how was I using it? I was checking to see which profiles existed in a database (the list was somewhat longer than this, as was the SQL, but this is good for a demo) so I generated my full list of known profiles to join to the existing profiles in each database.

WITH my_profiles AS (
    SELECT
        column_value AS profile_name
    FROM
        sys.odcivarchar2list(
            'DEFAULT'
          , 'SOME_OTHER_PROFILE' --etc etc etc 
        )
)
SELECT
    mp.profile_name
  , nvl( profile , '<does-not-exist>') AS profile
  , resource_name
  , limit
FROM
    my_profiles  mp
    LEFT OUTER JOIN dba_profiles dp ON ( mp.profile_name = dp.profile )
ORDER BY
    profile
  , resource_name;

PROFILE_NAME         PROFILE              RESOURCE_NAME                  LIMIT
-------------------- -------------------- ------------------------------ -----------
SOME_OTHER_PROFILE   <does-not-exist>
DEFAULT              DEFAULT              COMPOSITE_LIMIT                UNLIMITED
DEFAULT              DEFAULT              CONNECT_TIME                   UNLIMITED
DEFAULT              DEFAULT              CPU_PER_CALL                   UNLIMITED
DEFAULT              DEFAULT              CPU_PER_SESSION                UNLIMITED
DEFAULT              DEFAULT              FAILED_LOGIN_ATTEMPTS          10
DEFAULT              DEFAULT              IDLE_TIME                      UNLIMITED
DEFAULT              DEFAULT              INACTIVE_ACCOUNT_TIME          UNLIMITED
DEFAULT              DEFAULT              LOGICAL_READS_PER_CALL         UNLIMITED
DEFAULT              DEFAULT              LOGICAL_READS_PER_SESSION      UNLIMITED
DEFAULT              DEFAULT              PASSWORD_GRACE_TIME            7
DEFAULT              DEFAULT              PASSWORD_LIFE_TIME             180
DEFAULT              DEFAULT              PASSWORD_LOCK_TIME             1
DEFAULT              DEFAULT              PASSWORD_REUSE_MAX             UNLIMITED
DEFAULT              DEFAULT              PASSWORD_REUSE_TIME            UNLIMITED
DEFAULT              DEFAULT              PASSWORD_ROLLOVER_TIME         -1
DEFAULT              DEFAULT              PASSWORD_VERIFY_FUNCTION       NULL
DEFAULT              DEFAULT              PRIVATE_SGA                    UNLIMITED
DEFAULT              DEFAULT              SESSIONS_PER_USER              UNLIMITED

There’s a number of other ways to do this, including using the UNPIVOT function, creating your own table type, etc, but this was the nice and simple option I was looking for.

SQL Developer insight

When using SQL Developer, there is a feature called Completion Insight which help you write SQL and PL/SQL in the SQL Worksheets. It will auto-pop helpful things, like object name when typing a SELECT statement, column names if it is aware of the object which you are accessing and things like that.

The pop-up seems to pop-up inconsistently, appearing when I don’t want it and not appearing when I do. I finally snapped and decided to work out (look up) exactly how this feature works. And it’s like this.

1. Make sure your SQL is correctly formed. If you have multiple bits of SQL in the Worksheet, and they are not terminated with a “;” or “/“, then it can get confused about where you are contextually within a statement and not pop-up.

2. The Auto-popup has a delay of either 0.3s (SQL) or 0.6s (PL/SQL). This can be changed in Tools -> Preferences -> Code Editor -> Completion Insight. I have now set a 1.0s delay so it’s not quite so eager to appear.

3. You want the pop-up to appear? Press CTRL + SPACE. If it still does not appear, then it cannot determine your SQL Context (see point 1) or there’s nothing to pop.

Hope this helps you. It’s certainly helped me.

The 10046 trace. Largely useless, isn’t it?

The other night I was sat in the pub with some like-minded individuals discussing the relative merits of the 10046 trace (we Rock! in the pub, dudes!) and somebody asked me how often I has actually used it in anger? A well-respected DBA / Architect maintained it was a pretty useless and difficult option to use, given the topology of modern applications (e.g. How do you find the correct session with all that connection pooling going on from multiple web servers.)

My answer surprised me – I thought back to one client where I spent 90% of my time performance tuning a large (TiB-ish) OLTP/Batch hybrid system and concluded that I had ran a 10046 against production about once a year. Once. So if the 10046 is the holy grail of plan information, why wasn’t I using it that much. And why did I never use a 10053 against Production there?

The answer for me is a little more complex than that given in the pub:

1. as stated above, it’s hard to catch the in-flight session unless the application is instrumented to inject the trace statement when needed (and how many applications are instrumented to help you discover problems? Screen ST03 in SAP is very helpful. Any others in major ERP’s? Thought not.)

2. In many places that I have worked, getting authorisation to make any a change to a 24×7 mission-critical system is highly bureaucratic, involving cast-iron justification for the change and it’s positive benefits, requirement that there will be no adverse effects because of the change, very senior sign-off, more red-tape, etc. This causes a significant amount of work simply to put a trace on, even if you can catch the SQL. This can end up being more work than actually fixing the problem.

3. An awful lot of SQL tuning is a fairly blunt affair, as the developer (who is frequently database-blind) has usually missed something obvious. It is frequently to do with incorrectly using or not using an index (or using a poor index), or lack of filtering data at the right point to minimise the I/O.

4. Most importantly, if you have AWR and ASH, it’s not really needed. For each plan created by the optimizer the database stores the bind variables along with it, so we can usually understand why the optimizer makes the decisions it makes. ASH contains the main event waits. Why bother trying to capture all of the detail in a trace when you really don’t need that much detail, and it’s all already there; ready to be extracted from the relevant tables (e.g. dba_hist_active_sess_history, dba_hist_sql_plan and dba_hist_sql_bind.)

I have never used a 10053 trace on a Production system. I have simply never needed to know the decisions taken by the optimizer in that much detail. Like most DBA’s and Oracle consultants, I don’t go from site-to-site on a weekly basis resolving edge-case problems that the incumbent DBA’s haven’t had the time, or possibly don’t have the skills, to resolve themselves. I usually don’t need that level of confirmation that I’m right about why the plan is wrong, and I don’t have the time to conclusively prove it over and over again – I just need to get the fix into place and move onto the next problem.

That said, perhaps I should get fully to the bottom of these problems to ensure that they never occur again – which is the fundamental problem with Adaptive Cursor Sharing.