Learning is not a spectator sport
Connor McDonald on SQL and the Oracle Database
Statistics on Object tables
Way back in Oracle 8.0 we introduced the “Object-Relational” database, which was “the next big thing” in the database community back then. Every vendor was scrambling to show just how cool their database technology was with the object-oriented programming paradigm.
Don’t get me wrong – using the Oracle database object types and features associated with them has made my programming life a lot easier over the years. But for me, it’s always been pretty much limited to that, ie, programming, not actually using the object types in a database design as such. Nevertheless, using objects as columns, or even creating tables of objects is supported by the database. For example, I can create a object type of MY_OBJECT (which could itself be made up of objects) and then have a table, not with that object as a column, but actually a table of that object.
SQL> create type myobj as object ( x int, y int );
2 /
Type created.
SQL> create table t of myobj;
Table created.
To populate that table, I need to construct objects before they can be inserted, because are inserting objects not rows.
SQL> insert into t
2 select myobj(rownum,rownum)
3 from dual connect by level <= 10;
10 rows created.
Obviously, for good performance, we always need to gather optimizer statistics on database tables so that the optimizer can derive the best execution plans it can for any SQL statements that access this object table. Which leads to the question: Where can we see the optimizer statistics for an object table? Because once we get into object table territory, the first thing that normally takes DBAs and Developers by surprise is that the standard dictionary view for tables looks … sparse.
SQL> exec dbms_stats.gather_table_stats('','T');
PL/SQL procedure successfully completed.
SQL>
SQL> select *
2 from user_tables
3 where table_name = 'T';
no rows selected
A quick perusal of the documentation reveals where we can get information for object tables – and that is the aptly named USER_OBJECT_TABLES view
SQL> select *
2 from user_object_tables
3 where table_name = 'T'
4 @pr
==============================
TABLE_NAME : T
TABLESPACE_NAME : USERS
CLUSTER_NAME :
IOT_NAME :
STATUS : VALID
PCT_FREE : 10
PCT_USED :
INI_TRANS : 1
MAX_TRANS : 255
INITIAL_EXTENT : 65536
NEXT_EXTENT : 1048576
MIN_EXTENTS : 1
MAX_EXTENTS : 2147483645
PCT_INCREASE :
FREELISTS :
FREELIST_GROUPS :
LOGGING : YES
BACKED_UP : N
NUM_ROWS : 10
BLOCKS : 5
EMPTY_BLOCKS : 0
AVG_SPACE : 0
CHAIN_CNT : 0
AVG_ROW_LEN : 23
AVG_SPACE_FREELIST_BLOCKS : 0
NUM_FREELIST_BLOCKS : 0
DEGREE : 1
INSTANCES : 1
CACHE : N
TABLE_LOCK : ENABLED
SAMPLE_SIZE : 10
LAST_ANALYZED : 18-FEB-19
PARTITIONED : NO
IOT_TYPE :
OBJECT_ID_TYPE : SYSTEM GENERATED
TABLE_TYPE_OWNER : MCDONAC
TABLE_TYPE : MYOBJ
TEMPORARY : N
SECONDARY : N
NESTED : NO
BUFFER_POOL : DEFAULT
FLASH_CACHE : DEFAULT
CELL_FLASH_CACHE : DEFAULT
ROW_MOVEMENT : DISABLED
GLOBAL_STATS : YES
USER_STATS : NO
DURATION :
SKIP_CORRUPT : DISABLED
MONITORING : YES
CLUSTER_OWNER :
DEPENDENCIES : DISABLED
COMPRESSION : DISABLED
COMPRESS_FOR :
DROPPED : NO
SEGMENT_CREATED : YES
INMEMORY : DISABLED
INMEMORY_PRIORITY :
INMEMORY_DISTRIBUTE :
INMEMORY_COMPRESSION :
INMEMORY_DUPLICATE :
EXTERNAL : NO
CELLMEMORY :
INMEMORY_SERVICE :
INMEMORY_SERVICE_NAME :
MEMOPTIMIZE_READ : DISABLED
MEMOPTIMIZE_WRITE : DISABLED
HAS_SENSITIVE_COLUMN : NO
PL/SQL procedure successfully completed.
So far so good. But if I want to really dig down into optimizer statistics for table, I need to look further afield than just USER_TABLES and look at the dictionary views dedicated to just optimizer statistics information, and that is when things get a little interesting for object tables.
SQL> select *
2 from user_tab_statistics
3 where table_name = 'T';
no rows selected.
SQL> select *
2 from user_tab_col_statistics
3 where table_name = 'T'
4 @pr
==============================
TABLE_NAME : T
COLUMN_NAME : SYS_NC_OID$
NUM_DISTINCT : 10
LOW_VALUE : 265DF9DB62004A2B90B6FB3D550CB9FD
HIGH_VALUE : E868127216F045C89F54B55A48EAD6CF
DENSITY : .1
NUM_NULLS : 0
NUM_BUCKETS : 1
LAST_ANALYZED : 18-FEB-19
SAMPLE_SIZE : 10
GLOBAL_STATS : YES
USER_STATS : NO
NOTES :
AVG_COL_LEN : 17
HISTOGRAM : NONE
SCOPE : SHARED
==============================
TABLE_NAME : T
COLUMN_NAME : X
NUM_DISTINCT : 10
LOW_VALUE : C102
HIGH_VALUE : C10B
DENSITY : .1
NUM_NULLS : 0
NUM_BUCKETS : 1
LAST_ANALYZED : 18-FEB-19
SAMPLE_SIZE : 10
GLOBAL_STATS : YES
USER_STATS : NO
NOTES :
AVG_COL_LEN : 3
HISTOGRAM : NONE
SCOPE : SHARED
==============================
TABLE_NAME : T
COLUMN_NAME : Y
NUM_DISTINCT : 10
LOW_VALUE : C102
HIGH_VALUE : C10B
DENSITY : .1
NUM_NULLS : 0
NUM_BUCKETS : 1
LAST_ANALYZED : 18-FEB-19
SAMPLE_SIZE : 10
GLOBAL_STATS : YES
USER_STATS : NO
NOTES :
AVG_COL_LEN : 3
HISTOGRAM : NONE
SCOPE : SHARED
PL/SQL procedure successfully completed.
I can get column level statistics, but there is no entry in USER_TAB_STATISTICS for my object table. Checking the documentation indicates that unlike the USER_TABLES/USER_OBJECT_TABLES pairing, there is no partnering object-based view to match USER_TAB_STATISTICS. Digging into the definition for the USER_TAB_STATISTICS view shows that object tables are explicitly excluded:
and bitand(t.property, 1) = 0 /* not a typed table */
That might not seem such a big deal, but what happens if you lock the statistics for a table.
SQL> exec dbms_stats.lock_table_stats('','T');
PL/SQL procedure successfully completed.
The STATTYPE_LOCKED column is not on USER_TABLES and since we do not have an entry for the table in USER_TAB_STATISTICS, there is no direct mean of seeing if an object table has locked statistics. If you are faced with this problem, you have a couple of options at your disposal:
1) It would appear that the same flag on the internal dictionary table that indicates locked statistics is set for object tables as it would be for standard relational tables. Hence you could create a clone of the USER_TAB_STATISTICS view and remove the BITAND condition on the PROPERTY column. That of course is a very unsupported thing to do, and is just a rod for your back every time you patch or upgrade the database.
2) The other option is to assume that no-one is going to “mix and match” locking table statistics with index statistics. Every object table has an underlying index that is automatically created, so you can look at the locked status for this underlying index as a representative indicator of the table’s statistics locked state.
SQL> select *
2 from user_ind_statistics
3 where table_name = 'T'
4 @pr
==============================
INDEX_NAME : SYS_C0028743
TABLE_OWNER : MCDONAC
TABLE_NAME : T
PARTITION_NAME :
PARTITION_POSITION :
SUBPARTITION_NAME :
SUBPARTITION_POSITION :
OBJECT_TYPE : INDEX
BLEVEL : 0
LEAF_BLOCKS : 1
DISTINCT_KEYS : 10
AVG_LEAF_BLOCKS_PER_KEY : 1
AVG_DATA_BLOCKS_PER_KEY : 1
CLUSTERING_FACTOR : 1
NUM_ROWS : 10
AVG_CACHED_BLOCKS :
AVG_CACHE_HIT_RATIO :
SAMPLE_SIZE : 10
LAST_ANALYZED : 18-FEB-19
GLOBAL_STATS : YES
USER_STATS : NO
STATTYPE_LOCKED : ALL
STALE_STATS : NO
SCOPE : SHARED
PL/SQL procedure successfully completed.
TL;DR: Querying optimizer statistics for object tables takes a little more care than with normal tables.
MERGE and ORA-30926
Just a quick blog post on MERGE and the “unable to get a stable set of rows” error that often bamboozles people. This is actually just the script output from a pre-existing YouTube video (see below) that I’ve already done on this topic, but I had a few requests for the SQL example end-to-end, so here it is.
Imagine the AskTOM team had a simple table defining the two core members, Chris Saxon and myself. But in the style of my true Aussie laziness, I was very slack about checking the quality of the data I inserted.
SQL> create table oracle_team (
2 pk number primary key,
3 first_name varchar2(10),
4 last_name varchar2(10)
5 );
Table created.
SQL>
SQL> insert into oracle_team (pk, first_name, last_name) values (1, 'Connor', 'Macdonald');
1 row created.
SQL> insert into oracle_team (pk, first_name, last_name) values (3, 'kris', 'saxon');
1 row created.
SQL> commit;
Commit complete.
SQL> select * from oracle_team;
PK FIRST_NAME LAST_NAME
---------- ---------- ----------
1 Connor Macdonald
3 kris saxon
2 rows selected.
You can see that the data is garbage. Both of our names are wrong so they need fixing. So I build a table called FIXES which lets people “queue up” fix requests to the table. I’ll add the 2 obvious fixes to that table.
SQL> create table fixes (
2 team_pk number,
3 first_name varchar2(10),
4 last_name varchar2(10),
5 requested date
6 );
Table created.
SQL> insert into fixes values (1, 'Connor', 'McDonald',sysdate);
1 row created.
SQL> insert into fixes values (3, 'Chris', 'Saxon',sysdate);
1 row created.
SQL> commit;
Commit complete.
SQL> select * from fixes;
TEAM_PK FIRST_NAME LAST_NAME APPLIED
---------- ---------- ---------- ---------
1 Connor McDonald 18-FEB-19
3 Chris Saxon 18-FEB-19
2 rows selected.
To apply those fixes to the table, a simple MERGE command is all I need. Notice that MERGE does not have to be a “full” merge (ie, update AND insert), you can pick and choose what elements you want. MERGE is very powerful and flexible in that regard.
SQL>
SQL>
SQL> merge into oracle_team target
2 using (select team_pk, first_name, last_name
3 from fixes
4 ) source
5 on (target.pk = source.team_pk)
6 when matched then
7 update set
8 target.first_name = source.first_name,
9 target.last_name = source.last_name
10
SQL> pause
SQL> /
2 rows merged.
SQL>
SQL> select * from oracle_team;
PK FIRST_NAME LAST_NAME
---------- ---------- ----------
1 Connor McDonald
3 Chris Saxon
2 rows selected.
So all looks well. Let me now show how what seems like a simple repeat of that operation can get us into trouble. I’ve dropped all the tables, so that I can recreate the demo from scratch.
SQL>
SQL> create table oracle_team (
2 pk number primary key,
3 first_name varchar2(10),
4 last_name varchar2(10)
5 );
Table created.
SQL>
SQL> insert into oracle_team (pk, first_name, last_name) values (1, 'Connor', 'Macdonald');
1 row created.
SQL> insert into oracle_team (pk, first_name, last_name) values (3, 'kris', 'saxon');
1 row created.
SQL> commit;
Commit complete.
SQL> select * from oracle_team;
PK FIRST_NAME LAST_NAME
---------- ---------- ----------
1 Connor Macdonald
3 kris saxon
2 rows selected.
SQL> create table fixes (
2 team_pk number,
3 first_name varchar2(10),
4 last_name varchar2(10),
5 applied date
6 );
Table created.
This time we’ll assume that repeated fix requests have come in for a single AskTOM team member (PK=1). My first fix request was to the change the “Mac” to “Mc” in McDonald, but then I got all picky and realised that I’d like to have a capital “D” in McDonald. Fussy fussy fussy 
SQL> insert into fixes values (1, 'Connor', 'Mcdonald',sysdate-1);
1 row created.
SQL> insert into fixes values (1, 'Connor', 'McDonald',sysdate);
1 row created.
SQL> insert into fixes values (3, 'Chris', 'Saxon',sysdate);
1 row created.
SQL> commit;
Commit complete.
SQL> select * from fixes;
TEAM_PK FIRST_NAME LAST_NAME APPLIED
---------- ---------- ---------- ---------
1 Connor Mcdonald 17-FEB-19
1 Connor McDonald 18-FEB-19
3 Chris Saxon 18-FEB-19
3 rows selected.
SQL>
Look what happens now when I re-attempt the MERGE.
SQL>
SQL>
SQL> merge into oracle_team target
2 using (select team_pk, first_name, last_name
3 from fixes
4 ) source
5 on (target.pk = source.team_pk)
6 when matched then
7 update set
8 target.first_name = source.first_name,
9 target.last_name = source.last_name
10
SQL> pause
SQL> /
merge into oracle_team target
*
ERROR at line 1:
ORA-30926: unable to get a stable set of rows in the source tables
Conceptually this example (hopefully) makes it clear why the error occurred. Depending on which FIXES row for my row in the target table (PK=1) the database sees first, the end result of the MERGE could be different. And we really can’t allow that because it means the results are pseudo-random.
So how can we fix these things? We need a stable set of rows in the sense that the MERGE results should never be questionable based on order in which we process the input set of rows. In the example above, we could probably make an assumption that the last fix request for a given primary key value is the one that should always take precedence. Hence the source set of fixes can be altered as below.
SQL>
SQL>
SQL> select *
2 from
3 (select team_pk,
4 first_name,
5 last_name,
6 row_number() over ( partition by team_pk order by applied desc ) as r
7 from fixes
8 ) where r = 1;
TEAM_PK FIRST_NAME LAST_NAME R
---------- ---------- ---------- ----------
1 Connor McDonald 1
3 Chris Saxon 1
2 rows selected.
which then becomes an input into the MERGE command and the error is avoided.
SQL>
SQL> merge into oracle_team target
2 using
3 ( select *
4 from
5 (select team_pk,
6 first_name,
7 last_name,
8 row_number() over ( partition by team_pk order by applied desc ) as r
9 from fixes
10 ) where r = 1
11 ) source
12 on (target.pk = source.team_pk)
13 when matched then
14 update set
15 target.first_name = source.first_name,
16 target.last_name = source.last_name
17
SQL> /
2 rows merged.
SQL>
SQL> select * from oracle_team;
PK FIRST_NAME LAST_NAME
---------- ---------- ----------
1 Connor McDonald
3 Chris Saxon
2 rows selected.
The video walking through this demo came from an Office Hours session, and you can watch it below
The death of UTL_FILE – part 2
I wrote a post a while back call “The Death of UTL_FILE”, and probably because of it’s click-bait title I got lots of feedback, so I’m back to flog that horse 
. Seriously though, I stand behind my assertion in that post, that the majority of usages of UTL_FILE I’ve seen my career are mimicking the spooling behaviour of a SQL*Plus script. And as that post pointed out, you can now achieve that functionality directly with the scheduler.
That is well and good for writing files from the database, and I added:
“I’ll come back to UTL_FILE to read files in a future post”.
That time has come! Many developers will be aware of the feature known as external tables but a criticism of those has been that whereas UTL_FILE only needs permissions on the appropriate directory object to read a file, an external table requires a DDL definition, which typically means a lot of red tape and processes to follow when trying to implement changes.
Some of that pain was alleviated in 12c Release 2 when it became possible to modify portions of the external table definition on the fly at query execution time. For example, if you needed to change the name of the file name each day, then rather than having to re-craft an external table DDL, or even an ‘alter’ command, it could be done as required by the query:
SQL> select * from ext_emp
2 external modify ( location ('emp20161002.dat') );
EMPNO ENAME JOB MGR HIREDATE SAL
---------- ---------- --------- ---------- --------- ---------- ---
7902 FORD ANALYST 7566 03-DEC-81 3000
7934 MILLER CLERK 7782 23-JAN-82 1300
7566 JONES MANAGER 7839 02-APR-81 2975
That still of course does not alleviate the need for the initial table DDL. But in 18c, you can query an external file and the only thing you need to do so is appropriate privileges on the directory object. Sounds a lot like UTL_FILE, no? In 18c, we can query an external source directly with query. Here’s a simple example using the following data file (emp.dat) as a source:
7369,SMITH,CLERK,7902,800,,20
7499,ALLEN,SALESMAN,7698,1600,300,30
7521,WARD,SALESMAN,7698,1250,500,30
7566,JONES,MANAGER,7839,2975,,20
7654,MARTIN,SALESMAN,7698,1250,1400,30
7698,BLAKE,MANAGER,7839,2850,,30
7782,CLARK,MANAGER,7839,2450,,10
7788,SCOTT,ANALYST,7566,3000,,20
7839,KING,PRESIDENT,,5000,,10
7844,TURNER,SALESMAN,7698,1500,,30
7876,ADAMS,CLERK,7788,1100,,20
7900,JAMES,CLERK,7698,950,,30
7902,FORD,ANALYST,7566,3000,,20
7934,MILLER,CLERK,7782,1300,,10
The query (in this case) just requires the EXTERNAL modifier and a definition of the columns and we’re done!
SQL> select * from
2 external (
3 (
4 empno number(4),
5 ename varchar2(12),
6 job varchar2(12),
7 mgr number(4),
8 sal number(7,2),
9 comm number(7,2),
10 deptno number(2)
11 )
12 type oracle_loader
13 default directory TMP
14 location ('emp.dat')
15 );
EMPNO ENAME JOB MGR SAL COMM DEPTNO
---------- ------------ ------------ ---------- ---------- ---------- ----------
7369 SMITH CLERK 7902 800 20
7499 ALLEN SALESMAN 7698 1600 300 30
7521 WARD SALESMAN 7698 1250 500 30
7566 JONES MANAGER 7839 2975 20
7654 MARTIN SALESMAN 7698 1250 1400 30
7698 BLAKE MANAGER 7839 2850 30
7782 CLARK MANAGER 7839 2450 10
7788 SCOTT ANALYST 7566 3000 20
7839 KING PRESIDENT 5000 10
7844 TURNER SALESMAN 7698 1500 30
7876 ADAMS CLERK 7788 1100 20
7900 JAMES CLERK 7698 950 30
7902 FORD ANALYST 7566 3000 20
7934 MILLER CLERK 7782 1300 10
14 rows selected.
Of course, UTL_FILE is more about totally flexibility in the content your read. After all, you (typically) read a line from the file and then parse it however you please. But the same is possible with the 18c syntax. Here I’ll take some free format text from the Oracle documentation in a file plain.dat.
9.5 System Triggers
A system trigger is created on either a schema or the database.
Its triggering event is composed of either DDL statements (listed in "ddl_event") or database operation statements (listed in "database_event").
A system trigger fires at exactly one of these timing points:
Before the triggering statement runs
(The trigger is called a BEFORE statement trigger or statement-level BEFORE trigger.)
After the triggering statement runs
(The trigger is called a AFTER statement trigger or statement-level AFTER trigger.)
Instead of the triggering CREATE statement
(The trigger is called an INSTEAD OF CREATE trigger.)
Topics
SCHEMA Triggers
DATABASE Triggers
INSTEAD OF CREATE Triggers
9.5.1 SCHEMA Triggers
A SCHEMA trigger is created on a schema and fires whenever the user who owns it is the current user and initiates the triggering event.
Suppose that both user1 and user2 own schema triggers, and user1 invokes a DR unit owned by user2. Inside the DR unit, user2 is the current user. Therefore, if the DR unit initiates the triggering event of a schema trigger that user2 owns, then that trigger fires. However, if the DR unit initiates the triggering event of a schema trigger that user1 owns, then that trigger does not fire.
Example 9-19 creates a BEFORE statement trigger on the sample schema HR. When a user connected as HR tries to drop a database object, the database fires the trigger before dropping the object.
To mimic the line-by-line read style of UTL_FILE, I can simple define a single column holding a line from the data file.
SQL> select * from
2 external (
3 (
4 text varchar2(4000)
5 )
6 type oracle_loader
7 default directory TMP
8 location ('plain.dat')
9 );
TEXT
------------------------------------------------------------
9.5 System Triggers
A system trigger is created on either a schema or the databa
se.
Its triggering event is composed of either DDL statements (l
isted in "ddl_event") or database operation statements (list
ed in "database_event").
A system trigger fires at exactly one of these timing points
:
Before the triggering statement runs
(The trigger is called a BEFORE statement trigger or stateme
nt-level BEFORE trigger.)
After the triggering statement runs
(The trigger is called a AFTER statement trigger or statemen
t-level AFTER trigger.)
Instead of the triggering CREATE statement
(The trigger is called an INSTEAD OF CREATE trigger.)
Topics
SCHEMA Triggers
DATABASE Triggers
INSTEAD OF CREATE Triggers
9.5.1 SCHEMA Triggers
A SCHEMA trigger is created on a schema and fires whenever t
he user who owns it is the current user and initiates the tr
iggering event.
Suppose that both user1 and user2 own schema triggers
Example 9-19 creates a BEFORE statement trigger on the sampl
e schema HR. When a user connected as HR tries to drop a dat
abase object
18 rows selected.
So there is plenty of potential there to reduce the amount of source code to maintain using this nice syntax. The line between database data and external data gets blurrier, which is a great convenience for developers and ad-hoc users in being able to bring all the power of SQL to more data sources.
Footnote: When you query an external data source in 18c in the way mentioned above, behind the scenes, the database may create global temporary tables to support the operation. In the first example above, the database performed the following DDL recursively:
CREATE GLOBAL TEMPORARY TABLE "SCOTT"."SYS_TEMP_0FD9D678B_BDA818A8" SHARING=NONE
("EMPNO" NUMBER(4),
"ENAME" VARCHAR2(12) COLLATE "USING_NLS_COMP" ,
"JOB" VARCHAR2(12) COLLATE "USING_NLS_COMP" ,
"MGR" NUMBER(4),"SAL" NUMBER(7,2),
"COMM" NUMBER(7,2),
"DEPTNO" NUMBER(2)
)
IN_MEMORY_METADATA CURSOR_SPECIFIC_SEGMENT INLINE_XT
STORAGE (OBJNO 4254951307 ) NOPARALLEL
That should not be cause for concern, but if you have hundreds of differently structured external data sources, and/or triggers that fire on DDL operations on the database, then you might see some impact. As with all things, thorough testing should always precede production implementation.
Use the features available!
Advance warning: This post is a just another normal Friday morning rant. If you’re not interested in my pontificating, move along…nothing else to see here 
Sometimes you can’t make use of a facility that you normally would, and you have to substitute in something else. For example, if I would normally take the train to the basketball game, but today it’s not running due to track maintenance, then I’ll take the bus. I have no problem with that, because there’s a reason that I can’t take the train that day.
What does get my goat is on a day when the train is running, you come to me and say:
“Can you tell how to get the basketball game? Oh, by the way, I can’t take the train; I won’t use the bus; I don’t have a car; planes bother me; I get sea sick; I’m allergic to horses, and my feet hurt when I walk.”
Because all I’m thinking then is: “Then just don’t go to the damn game!”
So lets bring that metaphor into the world of Oracle. I always chuckle when AskTOM questions come in along the lines of:
“I need to achieve ‘X’. I have read that there is a feature ‘Y’ that achieves ‘X’. But I cannot use ‘Y'”
Don’t get me wrong. If there is a reason why “Y” is not a potential solution (eg, requires Enterprise Edition or perhaps an optional feature), then fine. We can then try work within those restrictions. But often what seems to be the case is that the statement:
“I cannot use ‘Y'”
is really just someone saying:
“I am not familiar with ‘Y’ so I’d rather not take the time and effort to become familiar with it”
and that’s…well…annoying.
No-one expects you to have immediate grasp and knowledge of the entire suite of features available in the Oracle database. I doubt that anyone does that breadth of knowledge. That is why we have the documentation; that is why we have community forums and sites like AskTOM, so that the collective knowledge of the community can be of assistance. But if you’re not prepared to spread your wings a little, and learn those new things, then you’re missing out on some of the great functionality available to you in the Oracle database.
AskTOM Question: How I can restrict the number of sessions a user has ?
Us: You can use a profile for this.
Response: I’d rather not use a profile
Us: OK then, then perhaps look at using Resource Manager to limit session activity.
Response: I’d rather not Resource Manager
Us: OK then, then perhaps look at using a logon trigger to perform your own custom logic to manage sessions.
Response: I don’t to write a trigger for this.
Us: Then just don’t go to the damn game!
The 19c database has just come out, and I know it’s always tempting just to focus on the new features that come with a release, but rest assured that inside Oracle, the focus for 19c was less on new features, but more on honing and improving the existing features in the Oracle database, to make them even more compelling solutions for your business requirements. But all of that won’t count for much if you’re not prepared to give them a chance.
DBMS_JOB is an asynchronous mechanism
One of the very cool things about DBMS_JOB is that a job does not “exist” as such until the session that submitted the job is commits the transaction. (This in my opinion is a critical feature that is missing from the DBMS_SCHEDULER package which, other than this omission, is superior to DBMS_JOB in every way).
Because DBMS_JOB is transactional, we can use it to make “non-transactional” things appear transactional. For example, if part of the workflow for hiring someone is to send an email to the Human Resources department, we can do the email via job submission so that an email is not sent if the employee record is not created successfully or is rolled back manually, eg:
begin
insert into EMP (empno, ename) values (123, 'CONNOR');
dbms_job.submit( :j,'notify_hr(empno=>123);');
end;
This post is not about that – that cool usage scenario is well known. But as a consequence, people tend to think that as soon as I commit, the job will spring into life. This is typically the case, but there are no guarantees that your job will run immediately, even if job queue processes are available.
Here’s a couple of examples of that in action
--
-- This one is almost instant
--
SQL> create table t
2 ( submitted timestamp,
3 started timestamp );
Table created.
SQL>
SQL> create or replace
2 procedure prc is
3 begin
4 update t set started = systimestamp;
5 commit;
6 end;
7 /
Procedure created.
SQL>
SQL> declare
2 j int;
3 begin
4 dbms_job.submit( j,'prc;');
5 insert into t(submitted) values (systimestamp);
6 commit;
7 end;
8 /
PL/SQL procedure successfully completed.
SQL>
SQL> col submitted format a32
SQL> col started format a32
SQL> select * from t;
SUBMITTED STARTED
-------------------------------- --------------------------------
13-FEB-19 09.31.10.956989 PM 13-FEB-19 09.31.10.994153 PM
--
-- This one not so much :-)
--
SQL> declare
2 j int;
3 begin
4 dbms_job.submit( j,'prc;');
5 insert into t(submitted) values (systimestamp);
6 commit;
7 end;
8 /
PL/SQL procedure successfully completed.
SQL>
SQL> col submitted format a32
SQL> col started format a32
SQL> select * from t;
SUBMITTED STARTED
-------------------------------- --------------------------------
14-FEB-19 01.22.45.928000 PM
SQL> /
SUBMITTED STARTED
-------------------------------- --------------------------------
14-FEB-19 01.22.45.928000 PM
SQL> /
SUBMITTED STARTED
-------------------------------- --------------------------------
14-FEB-19 01.22.45.928000 PM 14-FEB-19 01.22.59.775000 PM
In particular, I tend to notice this more on Windows platforms than others. MOS Note 2109840.1 is also a good starting point if you are seeing huge delays – you may have hit upon a bug.
So just be aware that DBMS_JOB will run your job soon after committing, but “soon” is a flexible term 
Work Life Travel balance
I thought about writing a post on juggling work commitments, travel with my job and time at home with children and family. And then I came across this post from community friend Robin Moffatt.
https://rmoff.net/2019/02/08/travelling-for-work-with-kids-at-home/
And … well … it’s exactly the thoughts, sentiments and motivation that I wanted to put in writing. Pretty much exactly. (Except the part about a spreadsheet – I’m a DBA, we don’t use spreadsheets…ever! 
). Robin will propbably be pissed with me saying this (because he writes some great tech stuff) but I reckon this post is his best work. It captures so well the importance of … the important stuff. This quote in particular is spot on:
In ten years who will give two monkeys if you presented at SuperKool Konference 2008? Conferences come and go. Kids just go
So true.
Hence I don’t need to write a post, because Robin has captured it perfectly. The only augmentation I have is due to the differences in ages of our children. Robin’s are 5 and 7, and mine are now 12 and 14. I’ve never been a huge fan of getting children onto the tech gadget bandwagon too soon, but now that mine are both in secondary school, I’ve changed that tune a little and got them a phone each. Obviously that comes with risks and the drawbacks that all kids tend to exhibit once they have phone (I’m looking at you Instagram and Snapchat!). But (for me) the positives of being able to reach out to the boys at a moment’s notice when I’m away outweighs that. Now I can immediately share with them the experiences of overseas adventures, and hopefully pique their interest to one day travel and explore the world when they’re older. Or even if it’s just a “Hey, I’ve just landed in transit in Dubai” it’s a reminder to them that their Dad is thinking about them when he’s away. Similarly, if they’re concerned about something or even stuck on their Maths homework, a quick Whatsapp or Telegram and we’re hooked up at least academically albeit not geographically. My next plan is to get them to occasionally come to these work trips with me; such experiences I think will be more benefit than the smattering of school days they might miss.
So kudos to Robin. If you travel for work, or even if you just work long hours – that post is well worth your time.
LISTAGG hits prime time
It’s a simple requirement. We want to transform this:
SQL> select deptno, ename
2 from emp
3 order by 1,2;
DEPTNO ENAME
---------- ----------
10 CLARK
10 KING
10 MILLER
20 ADAMS
20 FORD
20 JONES
20 SCOTT
20 SMITH
30 ALLEN
30 BLAKE
30 JAMES
30 MARTIN
30 TURNER
30 WARD
into this:
DEPTNO MEMBERS
---------- -------------------------------------
10 CLARK,KING,MILLER
20 SMITH,JONES,SCOTT,ADAMS,FORD
30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
Dinosaurs like myself remember the terrible trouble we used to go to in order to solve this seemingly simple problem. We could use the MODEL clause,
SQL> select deptno , rtrim(ename,',') enames
2 from ( select deptno,ename,rn
3 from emp
4 model
5 partition by (deptno)
6 dimension by (
7 row_number() over
8 (partition by deptno order by ename) rn
9 )
10 measures (cast(ename as varchar2(40)) ename)
11 rules
12 ( ename[any]
13 order by rn desc = ename[cv()]||','||ename[cv()+1])
14 )
15 where rn = 1
16 order by deptno;
DEPTNO ENAMES
---------- ----------------------------------------
10 CLARK,KING,MILLER
20 ADAMS,FORD,JONES,SCOTT,SMITH
30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
or we could use hierarchical trickery,
SQL> select deptno,
2 substr(max(sys_connect_by_path(ename, ',')), 2) members
3 from (select deptno, ename,
4 row_number ()
5 over (partition by deptno order by empno) rn
6 from emp)
7 start with rn = 1
8 connect by prior rn = rn - 1
9 and prior deptno = deptno
10 group by deptno
11 /
DEPTNO MEMBERS
---------- ---------------------------------------------------------
30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
20 SMITH,JONES,SCOTT,ADAMS,FORD
10 CLARK,KING,MILLER
or we could build our own aggregation routine from the ground up,
SQL> create or replace type string_agg_type as object
2 (
3 total varchar2(4000),
4
5 static function
6 ODCIAggregateInitialize(sctx IN OUT string_agg_type )
7 return number,
8
9 member function
10 ODCIAggregateIterate(self IN OUT string_agg_type ,
11 value IN varchar2 )
12 return number,
13
14 member function
15 ODCIAggregateTerminate(self IN string_agg_type,
16 returnValue OUT varchar2,
17 flags IN number)
18 return number,
19
20 member function
21 ODCIAggregateMerge(self IN OUT string_agg_type,
22 ctx2 IN string_agg_type)
23 return number
24 );
25 /
Or we had some sort of personality disorder 
then we could resort to manipulating some XML via XMLDB.
SQL> select deptno,
2 xmltransform
3 ( sys_xmlagg
4 ( sys_xmlgen(ename)
5 ),
6 xmltype
7 (
8 '<?xml version="1.0"?><xsl:stylesheet version="1.0"
9 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
10 <xsl:template match="/">
11 <xsl:for-each select="/ROWSET/ENAME">
12 <xsl:value-of select="text()"/>,</xsl:for-each>
13 </xsl:template>
14 </xsl:stylesheet>'
15 )
16 ).getstringval() members
17 from emp
18 group by deptno;
DEPTNO MEMBERS
---------- --------------------------------------------------------
10 CLARK,MILLER,KING,
20 SMITH,FORD,ADAMS,SCOTT,JONES,
30 ALLEN,JAMES,TURNER,BLAKE,MARTIN,WARD,
Thankfully all of these were solved once we made it to 11g with the simple LISTAGG function
SQL> select deptno,
2 listagg( ename, ',')
3 within group (order by empno) members
4 from emp
5 group by deptno;
DEPTNO MEMBERS
---------- -----------------------------------------
10 CLARK,KING,MILLER
20 SMITH,JONES,SCOTT,ADAMS,FORD
30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
I’ve always liked LISTAGG because the function reads like the business requirement we are trying to meet:
“AGG-regate a LIST of ENAMEs in sequence of EMPNO within the grouping of DEPTNO”
But there has been once problem with LISTAGG since it’s arrival in 11g, and that is what to do with duplicate data. Duplicates can either just look messy, for example, when I swap out ENAME for JOB:
SQL> select deptno
2 listagg(job,',') within group ( order by job) as jobs
3 from scott.emp
4 group by deptno
5 order by 1;
DEPTNO JOBS
--------- --------------------------------------------------
10 CLERK,MANAGER,PRESIDENT
20 ANALYST,ANALYST,CLERK,CLERK,MANAGER
30 CLERK,MANAGER,SALESMAN,SALESMAN,SALESMAN,SALESMAN
Or they could be even worse in the situation where the number of duplicates results in data exceeding allowing database limits. In the example below, there are hundreds of objects each with the same object type within a schema, and hence the aggregation blows the length limit for a varchar2.
SQL> select owner
2 listagg(object_type,',') within group
3 ( order by object_id ) as types
4 from all_ojects
5 group by owner
6 order by 1;
ERROR:
ORA-01499: result of string concatenation is too long
With 19c, our (technical) prayers have been answered with the long awaited arrival of the DISTINCT extension to the syntax.
SQL> select deptno,
2 listagg(distinct job,',') within group ( order by job ) as jobs
3 from scott.emp
4 group by deptno
5 order by 1;
DEPTNO JOBS
---------- ------------------------------------------------------------
10 CLERK,MANAGER,PRESIDENT
20 ANALYST,CLERK,MANAGER
30 CLERK,MANAGER,SALESMAN
3 rows selected.
SQL> select owner,
2 listagg(distinct object_type,',') within group ( order by object_type ) as types
3 from all_objects
4 group by owner
5 order by 1;
OWNER
------------------------------
TYPES
------------------------------------------------------------------------------------------------------------
------------
APPQOSSYS
SYNONYM,TABLE
AUDSYS
INDEX PARTITION,LIBRARY,PACKAGE,PACKAGE BODY,TABLE,TABLE PARTITION,VIEW
CTXSYS
FUNCTION,INDEX,INDEXTYPE,LIBRARY,OPERATOR,PACKAGE,PACKAGE BODY,PROCEDURE,SEQUENCE,TABLE,TYPE,TYPE BODY,VIEW
etc
Patch conflicts
My last post was about patching my home databases from 18.3 to 18.5 on Windows, and how I encountered a patch conflict when I tried to patch the JVM. I thought I’d give a little bit of info for anyone who runs into patch conflicts from time to time. It can be stressful especially if unforeseen, or you are in the middle of limited time outage window etc.
So before you jump into applying a patch, a nice little tool you might like to explore is the patch conflict checker on My Oracle Support. You can get it via:
https://support.oracle.com/epmos/faces/PatchConflictCheck
It is straightforward to use, you simply fill in the platform and your current patch inventory details, and then list out the patches you intend to apply.
One caveat – the online tool does not work with Windows environments 
but you can get around that by downloading the patches you intend to apply to your local machine. Then you can use opatch itself to perform that check:
opatch prereq CheckConflictAmongPatchesWithDetail -phBaseDir path
where “path” is where you have unzipped the patch to.
Like all patching activities, the more preparation work you can do before actually commencing the work, the more likely your chances of not encountering a sticky moment during the work.
From Database 18.3 to 18.5 (on Windows)
Contrary to wild rumours on the internet, it was not a fear of the number 13 that led to a numbering jump from version 12c to version 18c. The jump was part of our new, more flexible release mechanism so that we can get fixes and enhancements to customers on a more frequent and predictable schedule. In a nutshell, smaller bundles of features and fixes, more frequently.
I won’t dwell on that – if you’re unfamiliar with the new strategy, the best place to start is MOS Note 2285040.1, which has a description and a FAQ. But in terms of (as the saying goes) eating one’s own dog food, I downloaded the 18.5 release update which came out this week, and applied it to my 18.3 installation and I thought I’d share the process.
You might be wondering: “Why am I skipping 18.4?” Well that can be summarised simply as ignorance on my part – I missed the email a couple of few months back that told me 18.4 was available 
You might also be wondering: “I read that there were 4 release updates per year, how come there is an 18.5?” That is a common misinterpretation. We aim to provide a release update each quarter, but we never said that this means there would only ever be 4.
Now I stress – I’m just sharing my experiences here, not claiming that this is your go-to guide for applying the release update. I was just updating 18c on a Windows laptop, not a server. You should always follow the installation documents that come with the release update. For example, I had to reboot my Windows machine a couple of times, because it had transpired that some webcam software I’d installed had opted to use the Microsoft C++ shared libraries in my 18c Oracle Home! I think we can safely assume your servers probably don’t have webcams on them!
Step 1: Download a fresh OPatch
Seriously…just do this every time. As it turned out, my OPatch was already at a high enough level to apply the release update, but for me, years ago I adopted the mindset: “If I am going to apply a patch, then download a new OPatch“. It just makes it a no-brainer.
Step 2: Shut everything down.
I am running single instance, no “rolling” patching for me.
Step 3: Unzip the patch, set the environment, and patch
C:\>set ORACLE_HOME=C:\oracle\product\18
C:\>set PATH=%ORACLE_HOME%\OPatch;%ORACLE_HOME%\perl\bin;%PATH%
C:\>set PERL5LIB=
C:\>cd \oracle\stage\29124511
C:\oracle\stage\29124511>opatch apply
Oracle Interim Patch Installer version 12.2.0.1.14
Copyright (c) 2019, Oracle Corporation. All rights reserved.
Oracle Home : C:\oracle\product\18
Central Inventory : C:\Program Files\Oracle\Inventory
from :
OPatch version : 12.2.0.1.14
OUI version : 12.2.0.4.0
Log file location : C:\oracle\product\18\cfgtoollogs\opatch\opatch2019-01-18_09-36-46AM_1.log
Verifying environment and performing prerequisite checks...
Conflicts/Supersets for each patch are:
Patch : 29124511
Conflict with 28267731
Conflict details:
C:\oracle\product\18\javavm\admin\classes.bin
C:\oracle\product\18\javavm\admin\lfclasses.bin
C:\oracle\product\18\javavm\jdk\jdk8\admin\classes.bin
C:\oracle\product\18\javavm\jdk\jdk8\admin\lfclasses.bin
C:\oracle\product\18\rdbms\admin\oracle.sym
C:\oracle\product\18\bin\oracle.exe
Bug Superset of 27783303
Super set bugs are:
27748954, 27604293, 27747869, 27984028, 27550341, 27389352, 27433163, 27538461, 27341181,....
Well…that didn’t go so well Now the first thing confused me was: “How could there be any pre-existing patch to conflict with?”. After all, this was a complete 18c installation that I had downloaded from OTN when it first became available. But then I remembered, this is 18.3. So while it’s true that I download it as a standalone complete piece of software, it is still a patched release of the database. This is so much better than the old days where if you wanted (say) version 9.2.0.8, you had to download 9.2.0.1 and then apply the patch on top of it before using the software. A listing of the patch inventory showed that I already had some patches installed with my initial fresh download.
C:\oracle\stage\29124511>opatch lsinventory
Oracle Interim Patch Installer version 12.2.0.1.14
Copyright (c) 2019, Oracle Corporation. All rights reserved.
Oracle Home : C:\oracle\product\18
Central Inventory : C:\Program Files\Oracle\Inventory
from :
OPatch version : 12.2.0.1.14
OUI version : 12.2.0.4.0
Log file location : C:\oracle\product\18\cfgtoollogs\opatch\opatch2019-01-18_09-39-23AM_1.log
Lsinventory Output file location : C:\oracle\product\18\cfgtoollogs\opatch\lsinv\lsinventory2019-01-18_09-39-23AM.txt
--------------------------------------------------------------------------------
Local Machine Information::
Hostname: gtx
ARU platform id: 233
ARU platform description:: Microsoft Windows (64-bit AMD)
Installed Top-level Products (1):
Oracle Database 18c 18.0.0.0.0
There are 1 products installed in this Oracle Home.
Interim patches (3) :
Patch 28267731 : applied on Sat Aug 18 17:34:22 AWST 2018
Unique Patch ID: 22301563
Patch description: "WINDOWS OJVM BUNDLE PATCH : 18.3.0.0.180717 (28267731)"
Created on 8 Jul 2018, 06:48:38 hrs PST8PDT
Bugs fixed:
27642235, 27952586, 27304131, 27461740, 27636900, 27539876
This patch overlays patches:
27783303
This patch needs patches:
27783303
as prerequisites
Patch 27908644 : applied on Sat Aug 18 17:31:26 AWST 2018
Unique Patch ID: 22299245
Patch description: "UPDATE 18.3 DATABASE CLIENT JDK IN ORACLE HOME TO JDK8U171"
Created on 29 Jun 2018, 02:51:19 hrs PST8PDT
Bugs fixed:
27908644
Patch 27783303 : applied on Sat Aug 18 17:25:42 AWST 2018
Unique Patch ID: 22238986
Patch description: "Windows Database Bundle Patch : 18.3.0.0.180717 (27783303)"
Created on 16 Aug 2018, 07:58:43 hrs PST8PDT
Bugs fixed:
27026401, 27994333, 27680509, 27314206, 27345231, 24925863, 27447452
26792891, 27236110, 27608669, 27670484, 27421101, 27240246, 27213140
27740844, 27616657, 18701017, 27177852, 27697092, 27379956, 26598422
27688099, 27580996, 27534509, 27602488, 27333978, 27098733, 27163313
27551855, 27012915, 27603841, 27224987, 28165545, 27259983, 27919283
28039953, 27357773, 27302730, 27263996, 27345498, 27517818, 27377219
26882126, 27396377, 27701279, 27285557, 27779886, 27739006, 27585755
27321834, 27748954, 27950708, 26646549, 26961415, 27061736, 27066519
27498477, 28174926, 21806121, 24489904, 27570318, 27365139, 27028251
27435537, 27869339, 27226913, 27192754, 27038986, 27537472, 27483974
27329812, 27356373, 27714373, 27422874, 27334648, 27339115, 25035594
27128580, 27952762, 27691717, 27534289, 27425622, 27434974, 27518227
27426363, 27352600, 26450454, 27631506, 27143882, 27346949, 27181521
27199245, 27252023, 27911160, 27365702, 27497950, 26586174, 12816839
27389352, 25287072, 27215007, 27345190, 27475272, 25634405, 27813267
27726269, 27463879, 27086406, 27283029, 27850736, 27338838, 27428790
27395404, 27924147, 27284286, 27430254, 27262945, 27250547, 27346329
27693713, 27347126, 27745220, 27341036, 27481765, 28174827, 27450355
27214085, 27503413, 27451182, 27359178, 27625274, 27587672, 28320117
27367194, 27782464, 27735534, 27396365, 27210872, 27501327, 27984028
27309182, 27520070, 27999597, 27381383, 27302415, 27378103, 27861909
27782339, 27254851, 27086821, 27101273, 27465480, 27232983, 27941514
27486253, 27489719, 27222626, 27560562, 27244785, 27458829, 27262650
27155549, 25743479, 27897639, 27615608, 27459909, 27267992, 27304936
27663370, 27602091, 27448162, 27434486, 26933599, 26928317, 27586810
27153755, 27348081, 27314390, 27786669, 27573408, 27532375, 26818960
25824236, 27563767, 27060859, 27126666, 27284499, 27210038, 25726981
9062315, 27301308, 27725967, 27452760, 28188330, 27834984, 27748321
26990202, 27811439, 27376871, 27654039, 27080748, 27333664, 28059199
27420715, 27315159, 27331374, 27398660, 27680162, 25035599, 27718914
27599689, 27595801, 26615291, 27040560, 26476244, 27801774, 27450783
27066451, 27935826, 28098865, 26226953, 27501465, 27558559, 27496806
27381656, 27299455, 27124867, 27496224, 27707544, 27163928, 27147979
27395416, 27532009, 21766220, 27727843, 27607805, 27271876, 26860285
27997875, 28204423, 27204133, 27627992, 27592466, 27395794, 27430802
27511196, 27302800, 27204476, 27941896, 27560702, 27053044, 24689376
27447687, 27451049, 27302695, 26843664, 27181537, 27744211, 27445462
26427905, 27106915, 27896388, 27812593, 27926113, 27487795, 27135647
27496308, 28239335, 27452897, 26986173, 27434050, 27513114, 27114112
27265816, 27274536, 27396624, 28090453, 27396666, 27573409, 27331069
27379846, 27270197, 27016503, 27934468, 27595973, 27410595, 27833369
27577758, 26966120, 27757979, 27434193, 27393421, 27032726, 27613080
27208953, 27538461, 27581484, 27321179, 27263677, 26898279, 27573154
27492916, 27961746, 27591842, 27868727, 27047831, 27783289, 27405242
27970265, 27333693, 27506774, 27112686, 27379233, 27471876, 27425507
28205874, 27544030, 27401637, 27740854, 27993298, 27193810, 27212208
27184253, 27288230, 27399499, 27786772, 27978668, 26423085, 27873643
27481406, 27182006, 27547732, 27889841, 27169796, 27501413, 27679488
27518310, 27545630, 27346644, 27625010, 27360126, 27378959, 27772815
27525909, 27945870, 27275136, 27321575, 28182503, 26336101, 27216224
27375260, 27249544, 27174948, 27294480, 27957892, 27774539, 27664702
27839732, 27166715, 27432355, 27257509, 27657920, 27190851, 27773602
27774320, 27508936, 27457666, 27330161, 27339396, 27092991, 27101652
27803665, 27396672, 27472969, 27579969, 27610269, 27302594, 27778433
27339495, 25724089, 27739957, 28023410, 27433163, 27222121, 27851757
28109698, 27732323, 27691809, 27503208, 26822620, 28264172, 26846077
27189611, 27222423, 28132287, 27121566, 27282707, 27133637, 27451531
27613247, 27560735, 27702244, 27341181, 28240153, 27479358, 27370933
27396357, 27153641, 26827699, 27238258, 27364916, 27307868, 27791223
27041253, 27090765, 27892488, 27034318, 27349393, 27412805, 27399762
27302960, 27679664, 27815347, 27399985, 27241247, 26654411, 27077948
26987877, 27354783, 27701795, 27304410, 27882176, 27119621, 26956033
27300007, 27339165, 28106402, 27451187, 27058530, 21547051, 28025398
27682288, 27398080, 27586895, 27679806, 27164122, 27243810, 13554903
27993289, 27504190, 26587652, 27212837, 27274143, 27768034, 27550341
27558861, 27060167, 27600706, 28022847, 27241221, 27131377, 26992964
27690578, 27747407, 27305318, 27230645, 27818871, 27346709, 28057267
27405696, 27523368, 27574335, 27526362, 27174938, 27931506, 27392187
27221900, 27797290, 28184554, 27401618, 27410300, 26313403, 27864737
27362190, 27439835, 24737581, 27368850, 27593587, 27751006, 23840305
26996813, 27625050, 27657467, 27073066, 27302711, 27453225, 27984314
27274456, 27522245, 27417186, 27469329, 27338946, 27396813, 27786699
27285244, 27692215, 27519708, 23003564, 27339483, 27783059, 26882316
27757567, 26527054, 27862636, 27563629, 27635508, 27508985, 26785169
27472898, 27971575, 28413955, 27302681, 27609819, 27345450, 27788520
27018734, 27766679, 27101527, 27906509, 27593389, 27625620, 27036408
27358232, 27335682, 23698980, 27144533, 27585800, 27458164, 22734786
27523800, 28169711, 27384222, 27723002, 27473800, 27310092, 27604293
27731346, 27365993, 27005278, 27320985, 27445330, 27649707, 27709046
27313687, 27249215, 25348956, 27065091, 26433972, 27339654, 27318988
27333658, 27533819, 27403244, 27520900, 27534651, 27030974, 27427805
27359368, 23310101, 27644757, 27314512, 27044575, 27223171, 27240570
27156355, 27528204, 27989849, 27143756, 27679961, 27110878, 25943740
27747869, 27734470, 27283960, 27682151, 27719187, 26894737, 27869283
27652302, 27182064, 27467543, 27334353, 26843558, 27840386, 27457891
27334316, 27372756, 27705761, 27484556, 27708711, 27753336, 27364891
27964051, 27503318, 27423251, 27865439, 27780562, 26731697, 27358241
27634676, 27726780, 27444727, 27441326, 27326204, 27812560, 27432338
27577122, 27177551, 27275776, 27558557, 27375542, 26299684, 27301568
27593263, 27258578, 27222938, 27703242, 27512439, 27508984, 27398223
27330158, 27807441, 27079545, 27404599, 27259386, 27688692, 28039471
27292213, 27392256, 27307934, 27617522, 27505603, 27450400, 27348707
27460675, 27238077, 27346984, 27364947, 26943660, 27236052, 27338912
27244337, 28021205, 28032758, 28033429, 27263276, 27579353, 27233563
27220610, 28099592, 27433870, 27426277, 26647619, 27847259, 25929650
27738679, 27502420, 25709124, 28045209, 27668379, 27318869, 27832643
27302777, 28072130, 27442041, 27430219, 27614272, 27930478
--------------------------------------------------------------------------------
OPatch succeeded.
The conflict was with 28267731, which is the OJVM patch. I remembered from older 12c versions that the remedy to this was to rollback the older JVM patch before applying the new one. So I ran
C:\oracle\stage\29124511>opatch rollback -id 28267731
and then downloaded the 18.5 OJVM patch (28790647) as well in readiness.
After that, everything went as planned. I applied the DB patch and then applied the 18.5 OJVM patch. The final step was to open my database (and all of the pluggable database) and run in the database-level patch changes using datapatch
Microsoft Windows [Version 10.0.17134.523]
(c) 2018 Microsoft Corporation. All rights reserved.
C:\>set ORACLE_HOME=C:\oracle\product\18
C:\>set PATH=%ORACLE_HOME%\OPatch;%ORACLE_HOME%\perl\bin;%PATH%
C:\>set PERL5LIB=
C:\>cd C:\oracle\product\18\bin
C:\oracle\product\18\bin>sqlplus / as sysdba
SQL*Plus: Release 18.0.0.0.0 - Production on Fri Jan 18 12:33:19 2019
Version 18.5.0.0.0
Copyright (c) 1982, 2018, Oracle. All rights reserved.
Connected to:
Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production
Version 18.5.0.0.0
SQL> alter pluggable database all open;
Pluggable database altered.
SQL> exit
Disconnected from Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production
Version 18.5.0.0.0
C:\oracle\product\18\bin>cd %ORACLE_HOME%/OPatch
C:\oracle\product\18\OPatch>datapatch -verbose
SQL Patching tool version 18.0.0.0.0 Production on Fri Jan 18 12:33:32 2019
Copyright (c) 2012, 2019, Oracle. All rights reserved.
Log file for this invocation: C:\oracle\cfgtoollogs\sqlpatch\sqlpatch_16792_2019_01_18_12_33_32\sqlpatch_invocation.log
Connecting to database...OK
Gathering database info...done
Note: Datapatch will only apply or rollback SQL fixes for PDBs
that are in an open state, no patches will be applied to closed PDBs.
Please refer to Note: Datapatch: Database 12c Post Patch SQL Automation
(Doc ID 1585822.1)
Bootstrapping registry and package to current versions...done
Determining current state...done
Current state of interim SQL patches:
Interim patch 28267731 (WINDOWS OJVM BUNDLE PATCH : 18.3.0.0.180717 (28267731)):
Binary registry: Not installed
PDB CDB$ROOT: Applied successfully on 23-AUG-18 10.31.18.372000 AM
PDB PDB$SEED: Applied successfully on 23-AUG-18 10.36.41.858000 AM
PDB PDB1: Applied successfully on 23-AUG-18 10.36.41.858000 AM
Interim patch 28790647 (OJVM RELEASE UPDATE: 18.5.0.0.190115 (28790647)):
Binary registry: Installed
PDB CDB$ROOT: Not installed
PDB PDB$SEED: Not installed
PDB PDB1: Not installed
Current state of release update SQL patches:
Binary registry:
18.5.0.0.0 Release_Update 1812202039: Installed
PDB CDB$ROOT:
Applied 18.3.0.0.0 Release_Update 1808132056 successfully on 23-AUG-18 10.31.18.366000 AM
PDB PDB$SEED:
Applied 18.3.0.0.0 Release_Update 1808132056 successfully on 23-AUG-18 10.36.41.852000 AM
PDB PDB1:
Applied 18.3.0.0.0 Release_Update 1808132056 successfully on 23-AUG-18 10.36.41.852000 AM
Adding patches to installation queue and performing prereq checks...done
Installation queue:
For the following PDBs: CDB$ROOT PDB$SEED PDB1
The following interim patches will be rolled back:
28267731 (WINDOWS OJVM BUNDLE PATCH : 18.3.0.0.180717 (28267731))
Patch 29124511 (Windows Database Bundle Patch : 18.5.0.0.190115 (29124511)):
Apply from 18.3.0.0.0 Release_Update 1808132056 to 18.5.0.0.0 Release_Update 1812202039
The following interim patches will be applied:
28790647 (OJVM RELEASE UPDATE: 18.5.0.0.190115 (28790647))
Installing patches...
Patch installation complete. Total patches installed: 9
Validating logfiles...done
Patch 28267731 rollback (pdb CDB$ROOT): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\28267731\22301563/28267731_rollback_DB18_CDBROOT_2019Jan18_12_34_14.log (no errors)
Patch 29124511 apply (pdb CDB$ROOT): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\29124511\22646084/29124511_apply_DB18_CDBROOT_2019Jan18_12_34_47.log (no errors)
Patch 28790647 apply (pdb CDB$ROOT): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\28790647\22646085/28790647_apply_DB18_CDBROOT_2019Jan18_12_35_21.log (no errors)
Patch 28267731 rollback (pdb PDB$SEED): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\28267731\22301563/28267731_rollback_DB18_PDBSEED_2019Jan18_12_35_23.log (no errors)
Patch 29124511 apply (pdb PDB$SEED): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\29124511\22646084/29124511_apply_DB18_PDBSEED_2019Jan18_12_35_37.log (no errors)
Patch 28790647 apply (pdb PDB$SEED): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\28790647\22646085/28790647_apply_DB18_PDBSEED_2019Jan18_12_36_07.log (no errors)
Patch 28267731 rollback (pdb PDB1): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\28267731\22301563/28267731_rollback_DB18_PDB1_2019Jan18_12_35_24.log (no errors)
Patch 29124511 apply (pdb PDB1): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\29124511\22646084/29124511_apply_DB18_PDB1_2019Jan18_12_35_41.log (no errors)
Patch 28790647 apply (pdb PDB1): SUCCESS
logfile: C:\oracle\cfgtoollogs\sqlpatch\28790647\22646085/28790647_apply_DB18_PDB1_2019Jan18_12_36_12.log (no errors)
SQL Patching tool complete on Fri Jan 18 12:36:17 2019
C:\oracle\product\18\OPatch>
C:\oracle\product\18\OPatch>
C:\oracle\product\18\OPatch>sqlplus / as sysdba
SQL*Plus: Release 18.0.0.0.0 - Production on Fri Jan 18 12:36:28 2019
Version 18.5.0.0.0
Copyright (c) 1982, 2018, Oracle. All rights reserved.
Connected to:
Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production
Version 18.5.0.0.0
SQL> shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 2936010432 bytes
Fixed Size 9033408 bytes
Variable Size 1023410176 bytes
Database Buffers 1895825408 bytes
Redo Buffers 7741440 bytes
Database mounted.
Database opened.
SQL> alter pluggable database all open;
Pluggable database altered.
SQL> @?/rdbms/admin/utlrp.sql
Session altered.
TIMESTAMP
----------------------------------------------------------------------------------------------------------------------------------
COMP_TIMESTAMP UTLRP_BGN 2019-01-18 12:37:58
DOC> The following PL/SQL block invokes UTL_RECOMP to recompile invalid
DOC> objects in the database. Recompilation time is proportional to the
DOC> number of invalid objects in the database, so this command may take
DOC> a long time to execute on a database with a large number of invalid
DOC> objects.
DOC>
DOC> Use the following queries to track recompilation progress:
DOC>
DOC> 1. Query returning the number of invalid objects remaining. This
DOC> number should decrease with time.
DOC> SELECT COUNT(*) FROM obj$ WHERE status IN (4, 5, 6);
DOC>
DOC> 2. Query returning the number of objects compiled so far. This number
DOC> should increase with time.
DOC> SELECT COUNT(*) FROM UTL_RECOMP_COMPILED;
DOC>
DOC> This script automatically chooses serial or parallel recompilation
DOC> based on the number of CPUs available (parameter cpu_count) multiplied
DOC> by the number of threads per CPU (parameter parallel_threads_per_cpu).
DOC> On RAC, this number is added across all RAC nodes.
DOC>
DOC> UTL_RECOMP uses DBMS_SCHEDULER to create jobs for parallel
DOC> recompilation. Jobs are created without instance affinity so that they
DOC> can migrate across RAC nodes. Use the following queries to verify
DOC> whether UTL_RECOMP jobs are being created and run correctly:
DOC>
DOC> 1. Query showing jobs created by UTL_RECOMP
DOC> SELECT job_name FROM dba_scheduler_jobs
DOC> WHERE job_name like 'UTL_RECOMP_SLAVE_%';
DOC>
DOC> 2. Query showing UTL_RECOMP jobs that are running
DOC> SELECT job_name FROM dba_scheduler_running_jobs
DOC> WHERE job_name like 'UTL_RECOMP_SLAVE_%';
DOC>#
PL/SQL procedure successfully completed.
TIMESTAMP
----------------------------------------------------------------------------------------------------------------------------------
COMP_TIMESTAMP UTLRP_END 2019-01-18 12:38:01
DOC> The following query reports the number of invalid objects.
DOC>
DOC> If the number is higher than expected, please examine the error
DOC> messages reported with each object (using SHOW ERRORS) to see if they
DOC> point to system misconfiguration or resource constraints that must be
DOC> fixed before attempting to recompile these objects.
DOC>#
OBJECTS WITH ERRORS
-------------------
0
DOC> The following query reports the number of exceptions caught during
DOC> recompilation. If this number is non-zero, please query the error
DOC> messages in the table UTL_RECOMP_ERRORS to see if any of these errors
DOC> are due to misconfiguration or resource constraints that must be
DOC> fixed before objects can compile successfully.
DOC> Note: Typical compilation errors (due to coding errors) are not
DOC> logged into this table: they go into DBA_ERRORS instead.
DOC>#
ERRORS DURING RECOMPILATION
---------------------------
0
Function created.
PL/SQL procedure successfully completed.
Function dropped.
PL/SQL procedure successfully completed.
SQL>
================================
And that was all there was to it. I’ve now picked up over a 1000 fixes and improvements to the software. If you are one of those people who likes to patch rarely, I strongly recommend you have a re-think and take a closer look at the release update cycle. We want to get you better software, faster.
Enjoy your 18.5 release!
EXPORT not GATHER with DBMS_STATS
Just a short post today on something that came in as a question for the upcoming Office Hours session which I thought could be covered quickly in a blog post without needing a lot of additional discussion for which Office Hours is more suited to.
The question was:
“When I gather statistics using DBMS_STATS, can I just create a statistic table and pass that as a parameter to get the results of the gather”
And the answer simply is “No” 
but let me clear up the confusion.
Many DBMS_STATS routines allow you to pass the name of the “statistics table” into which statistical information for the table, schema, database etc will be stored. For example, you can see the STAT-prefixed parameter to GATHER_TABLE_STATS
PROCEDURE GATHER_TABLE_STATS
Argument Name Type In/Out Default?
------------------------------ ----------------------- ------ --------
OWNNAME VARCHAR2 IN
TABNAME VARCHAR2 IN
PARTNAME VARCHAR2 IN DEFAULT
ESTIMATE_PERCENT NUMBER IN DEFAULT
BLOCK_SAMPLE BOOLEAN IN DEFAULT
METHOD_OPT VARCHAR2 IN DEFAULT
DEGREE NUMBER IN DEFAULT
GRANULARITY VARCHAR2 IN DEFAULT
CASCADE BOOLEAN IN DEFAULT
STATTAB VARCHAR2 IN DEFAULT
STATID VARCHAR2 IN DEFAULT
STATOWN VARCHAR2 IN DEFAULT
NO_INVALIDATE BOOLEAN IN DEFAULT
STATTYPE VARCHAR2 IN DEFAULT
FORCE BOOLEAN IN DEFAULT
CONTEXT CCONTEXT IN DEFAULT
OPTIONS VARCHAR2 IN DEFAULT
The statistics table must be of a certain structure, which is managed via the API as well using the CREATE_STAT_TABLE routine.
SQL> exec dbms_stats.create_stat_table('','st')
PL/SQL procedure successfully completed.
SQL> desc ST
Name Null? Type
----------------------------- -------- --------------------
STATID VARCHAR2(128)
TYPE CHAR(1)
VERSION NUMBER
FLAGS NUMBER
C1 VARCHAR2(128)
C2 VARCHAR2(128)
C3 VARCHAR2(128)
C4 VARCHAR2(128)
C5 VARCHAR2(128)
C6 VARCHAR2(128)
N1 NUMBER
N2 NUMBER
N3 NUMBER
N4 NUMBER
N5 NUMBER
N6 NUMBER
N7 NUMBER
N8 NUMBER
N9 NUMBER
N10 NUMBER
N11 NUMBER
N12 NUMBER
N13 NUMBER
D1 DATE
T1 TIMESTAMP(6) WITH TI
ME ZONE
R1 RAW(1000)
R2 RAW(1000)
R3 RAW(1000)
CH1 VARCHAR2(1000)
CL1 CLOB
BL1 BLOB
But when calling the GATHER_xxx routines, if you pass the name of the statistic table, please note that this is for getting a copy of the relevant statistics before the fresh gathering of statistics is done. We can see this with a simple demo.
SQL> create table t1 as select * from dba_objects;
Table created.
SQL>
SQL> select num_rows
2 from user_tables
3 where table_name = 'T1';
NUM_ROWS
----------
83608
1 row selected.
So we can see that the table T1 has ~83,000 rows in it. Since I’m running this on 12c, there was no need to gather statistics after this initial load, because they were collected automatically as part of the loading process. (Very nifty!).
I now add another ~250,000 rows and perform a new GATHER_TABLE_STATS call, this time passing in the name of the statistics table (ST) that I just created.
SQL>
SQL> insert into t1
2 select * from t1;
83608 rows created.
SQL>
SQL> insert into t1
2 select * from t1;
167216 rows created.
SQL>
SQL> begin
2 dbms_stats.gather_table_stats
3 ( ownname=>'MCDONAC',
4 tabname=>'T1',
5 stattab=>'ST',
6 statid=>'STATS'
7 );
8 end;
9 /
PL/SQL procedure successfully completed.
Digging into the statistic table data, you can see that the number of rows recorded for T1 is 83597, which is the before image of the optimizer stat, not the after image.
SQL> select * from st where c1 = 'T1' and type = 'T'
2 @pr
==============================
STATID : STATS
TYPE : T
VERSION : 8
FLAGS : 2
C1 : T1
C2 :
C3 :
C4 :
C5 : MCDONAC
C6 :
N1 : 83597
N2 : 1607
N3 : 129
N4 : 83597
N5 :
N6 :
N7 :
N8 :
N9 : 0
N10 :
N11 :
N12 :
N13 :
D1 : 16-JAN-19
T1 :
R1 :
R2 :
R3 :
CH1 :
CL1 :
BL1 :
PL/SQL procedure successfully completed.
So just remember that if you want to get the DBMS_STATS information that is the result of a GATHER_xxx call, then you can follow it up with the appropriate EXPORT_xxx call to dump the data.
My APEX was fine and then it wasn’t
I got a nasty shock this morning when I fired up my local Application Expression installation.
It had been working fine and all of a sudden…just dead. I sounded like all of those family members that as I.T practitioners we have to deal with (and that we’re so sceptical of) when they say: “I didn’t change anything…it just stopped!” 
In keeping with the treatment of family members, I then adopted the advice that I normally give them first.
and upon restart, I saw the following during the startup
C:\oracle\ords181>java -jar ords.war standalone
2019-01-11 11:47:36.071:INFO::main: Logging initialized @1378ms to org.eclipse.jetty.util.log.StdErrLog
Jan 11, 2019 11:47:36 AM
INFO: HTTP and HTTP/2 cleartext listening on port: 8080
Jan 11, 2019 11:47:36 AM
INFO: The document root is serving static resources located in: C:\oracle\ords181\conf\ords\standalone\doc_root
2019-01-11 11:47:36.409:INFO:oejs.Server:main: jetty-9.4.z-SNAPSHOT, build timestamp: 2017-11-22T05:27:37+08:00, git hash: 82b8fb23f757335bb3329d540ce37a2a2615f0a8
2019-01-11 11:47:36.422:INFO:oejs.session:main: DefaultSessionIdManager workerName=node0
2019-01-11 11:47:36.423:INFO:oejs.session:main: No SessionScavenger set, using defaults
2019-01-11 11:47:36.423:INFO:oejs.session:main: Scavenging every 600000ms
Jan 11, 2019 11:47:37 AM
WARNING: The pool named: |apex|| is invalid and will be ignored: The connection pool named: apex is not correctly configured, due to the following error(s): ORA-28001: the password has expired
Jan 11, 2019 11:47:37 AM
WARNING: The pool named: |apex|al| is invalid and will be ignored: The connection pool named: apex_al is not correctly configured, due to the following error(s): ORA-28001: the password has expired
Since security is our #1 thing for 2019 and probably should be the #1 item on your agenda for 2019, this was caused by some improvements to the Oracle defaults when you perform a database installation. Rather than the default being an “flexible” (aka loose ) policy we used to have when it comes to password management, we’ve gone for some more sensible options out of the box.
SQL> select * from dba_profiles order by 1,2
PROFILE RESOURCE_NAME RESOURCE LIMIT
---------------- -------------------------------- -------- -----------
DEFAULT COMPOSITE_LIMIT KERNEL UNLIMITED
DEFAULT CONNECT_TIME KERNEL UNLIMITED
DEFAULT CPU_PER_CALL KERNEL UNLIMITED
DEFAULT CPU_PER_SESSION KERNEL UNLIMITED
DEFAULT FAILED_LOGIN_ATTEMPTS PASSWORD 10
DEFAULT IDLE_TIME KERNEL UNLIMITED
DEFAULT INACTIVE_ACCOUNT_TIME PASSWORD UNLIMITED
DEFAULT LOGICAL_READS_PER_CALL KERNEL UNLIMITED
DEFAULT LOGICAL_READS_PER_SESSION KERNEL UNLIMITED
DEFAULT PASSWORD_GRACE_TIME PASSWORD 7
DEFAULT PASSWORD_LIFE_TIME PASSWORD 180
DEFAULT PASSWORD_LOCK_TIME PASSWORD 1
DEFAULT PASSWORD_REUSE_MAX PASSWORD UNLIMITED
DEFAULT PASSWORD_REUSE_TIME PASSWORD UNLIMITED
DEFAULT PASSWORD_VERIFY_FUNCTION PASSWORD NULL
DEFAULT PRIVATE_SGA KERNEL UNLIMITED
DEFAULT SESSIONS_PER_USER KERNEL UNLIMITED
So if you want your APEX public accounts (and I stress, no others!) to have a non-expiring password, then you should create a custom profile for those accounts and assign them accordingly.
create profile no_expire
limit password_life_time unlimited;
alter user apex_public_user profile no_expire ;
alter user apex_rest_public_user profile no_expire ;
alter user apex_listener profile no_expire ;
alter user ords_public_user profile no_expire ;
This will ensure you don’t get an unexpected drama next time you want to fire up Application Express.
2018-what grabbed your attention
Here are the blog posts that you hit on most this year, with the most viewed entry on top. Unsurprisingly it is about the release of 18c, but interestingly the ORA-14758 and the Active Sessions post have come up again from last years list, so it appears they are still common issues for the modern Oracle professional. And of course, it is nice to see that my Openworld Mega-download is helping the community.
Thanks for supporting the blog, and as always, there will be more content next year !
