Direct Path Inserts = By DBWR or by Shadow Process

Hello guys,
if i use the append hint (direct path inserts) - which process is writting the data to the datafile?
In the documentation of oracle:
http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96524/c21dlins.htm#10778
Oracle appends the inserted data after existing data in the table. Data is written directly into datafiles, bypassing the buffer cache Ok that is clear - but who is writing down the data? The shadow process which is handling the insert statement or is it given to the dbwr and it flushes the data directly to the datatfile without putting it into the buffer cache.
And another question regarding direct path inserts:
http://sai-oracle.blogspot.com/2006/03/parallel-query-is-it-good-or-bad.html
If you want to do direct path insert in parallel, you would block all other non direct path insert operations on that table. This is because direct path insert would append above highwater mark, and no other process is allowed to update HWM until your operation is doneIf i insert data in serial with direct path insert... i also write data behind the High-HWM .. why is it only locked in parallel mode?
And why does oracle not check if there is enough space in some other blocks below the High-HWM and using these blocks for "normal" inserts?
Regards
Stefan

It's the server process that's responsible for writing direct path blocks to disk.
DBWR only ever flushes out of the buffer cache.
You do NOT write "data behind the HWM" in direct path mode, ever. Direct path works so fast because all you do is slam whole blocks of data onto disk ABOVE the high water mark. You can slam whole blocks down without worrying about what you're over-writing precisely because the blocks are above the HWM and thus cannot possibly be in use by anyone for anything. Under the HWM and you have to start worrying about locking and contention and stuff like that.
Parallel operations (or simultaneous serial operations by two different users) inevitably have to block each other for this sort of thing: if I am busy writing to blocks above the HWM, great. But if you want to do it too... well, what's to stop us from over-writing each other's blocks?! Nothing, actually. So Oracle simply has to lock the entire table from any other direct path operation to make the situation manageable.

Similar Messages

Insert /*+ Append */ and direct-path INSERT

Hi Guys
Does insert /*+ Append */ into hint cause Oracle 10G to use direct-path INSERT?
and if insert /*+ Append */ into hint does cause Oracle to use direct-path INSERT, does insert /*+ Append */ is subject to the same restrictions as direct-path such as "The target table cannot have any triggers or referential integrity constraints defined on it."
Thanks

Dear,
Here below a simple example showing the effet of existing trigger on the append hint
mhouri@mhouri> select * from v$version where rownum=1;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
mhouri@mhouri> create table b as select * from all_objects where 1 = 2;
Table créée.
mhouri@mhouri> insert /*+ append */ into b
2 select * from all_objects;
70986 ligne(s) créée(s).
mhouri@mhouri> select * from b;
select * from b
ERREUR à la ligne 1 :
ORA-12838: impossible de lire/modifier un objet après modification en parallèle
mhouri@mhouri> rollback;
Annulation (rollback) effectuée.The direct path took place as far as I can't select from the table before I commit
mhouri@mhouri> create trigger b_trg before insert on b
2 for each row
3 begin
4 null;
5 end;
6 /
Déclencheur créé.
mhouri@mhouri> insert /*+ append */ into b
2 select * from all_objects;
70987 ligne(s) créée(s).
424 ligne(s) sélectionnée(s).
mhouri@mhouri> select count(1) from b;
COUNT(1)
     70987                                                                      While in the presence of this trigger on the table, the append hint has been silently ignored by Oracle. The fact that I can select from the table immediately afte the insert has finished is the indication that the table has not be inserted using direct path load
Best Regards
Mohamed Houri

Direct path insert

Hi Friends,
If i used direct path insert from a (LAN) remote table with 5 million rows using:
sql> insert /*+ append */ into EMP using select * from EMP@dblink1;
1) Do i need to create big rollback segment?
*Note that in direct path sqlloader, no big rollback is needed.
2.) Can i still undo it or rollback it the 5 millions rows?
If i can then it sure holds or need a big rollback segment.
Thanks a lot
Message was edited by:
[email protected]

From same link see below points from Tom
b) a direct path load always loads above the high water mark, since it is formatting and writing blocks directly to disk - it cannot reuse any existing space. Think about this - if you direct pathed an insert of a 100 byte row that loaded say just two rows - and you did that 1,000 times, you would be using at least 1,000 blocks (never reuse any existing space) - each with two rows. Now, if you did that using a conventional path insert - you would get about 70/80 rows per block in an 8k block database. You would use about 15 blocks. Which would you prefer?+
c) you cannot query a table after direct pathing into it until you commit.+
See point c. So, this will mark block header transaction flag to commit. if you rollback as they are written above HWM and since there is no commit flag yet it just need to set table HWM to original one and that's it.

Forcing DIRECT PATH INSERT to go CONVENTIONAL.

According to Oracle, to force a statement to avoid using DIRECT-PATH insert it must fall into the following:
Direct-path INSERT is subject to a number of restrictions. If any of these restrictions is violated, then Oracle Database executes conventional INSERT serially without returning any message, unless otherwise noted:
    *     You can have multiple direct-path INSERT statements in a single transaction, with or without other DML statements. However, after one DML statement alters a particular table, partition, or index, no other DML statement in the transaction can access that table, partition, or index.
    *      Queries that access the same table, partition, or index are allowed before the direct-path INSERT statement, but not after it.
    *      If any serial or parallel statement attempts to access a table that has already been modified by a direct-path INSERT in the same transaction, then the database returns an error and rejects the statement.
    *      The target table cannot be part of a cluster.
    *      The target table cannot contain object type columns.
    *      Direct-path INSERT is not supported for an index-organized table (IOT) if it is not partitioned, if it has a mapping table, or if it is reference by a materialized view.
    *      Direct-path INSERT into a single partition of an index-organized table (IOT), or into a partitioned IOT with only one partition, will be done serially, even if the IOT was created in parallel mode or you specify the APPEND hint. However, direct-path INSERT operations into a partitioned IOT will honor parallel mode as long as the partition-extended name is not used and the IOT has more than one partition.
    *      The target table cannot have any triggers or referential integrity constraints defined on it.
    *      The target table cannot be replicated.
    *      A transaction containing a direct-path INSERT statement cannot be or become distributed.Are there any others that are not documented here? We have a vendor based app and want to avoid the DIRECT PATH INSERT and have it go CONVENTIONAL. We tried the TRIGGER approach, but that did not help at all.

Why are you wanting to force conventional ?
Are you sure the application uses direct path ?

Archive log / nologging/ direct path insert

Could you please confirm if following are true or correct me if my understanding is wrong:
1 ) Archive log mode and LOGGING is needed to deal with media recovery; it was not needed for instance recovery.
2) IF insert is in NO APPEND mode , redo is generated even if table is in nologging mode and database is in noachive log mode. This redo is needed for instance recovery.
3) Direct path insert skips undo generation and may skip redo generation if the object is in nologging mode.
Thanks.
In case if it is relevant , I am using Oracle 11.2.0.3.

1) Yes, Archive logs are needed for media recovery.
2 and 3) Even if the table is in nologging mode , it generates little bit of redo for index maintenance and dictionary data. Upon a restart from a failure - Oracle will read the online redo logs and replay any transaction it finds in there. That is the "roll forward" bit. The binary redo information is used to replay everything that did not get written to the datafiles. This replay included regenerating the UNDO information (UNDO is protected by redo).
After the redo has been applied, the database is typically available for use now - and the rollback phase begins. For any transaction that was being processed when the instance failed - we need to undo its changes, roll it back. We do that by processing the undo for all uncommitted transactions.
The database is now fully recovered.
Also read he following link
http://docs.oracle.com/cd/B19306_01/server.102/b14220/startup.htm
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:5280714813869

Direct path read caused by direct path insert?

Oracle 9.2
========
Consider this INSERT statement
INSERT /*+ APPEND USE_HASH*/ INTO schema.tablename (...)
SELECT * FROM view_tablename;
This statement takes about 30 minutes to complete.
If I look at the v$session_wait, I can see that the session waits denoting db file scattered read (which is understandable). However, at the very end of the 30-minute wait, the v$session_wait view shows that it is waiting denoting direct path read. I want to understand how can a direct path INSERT (or for that matter a simple INSERT statement) can cause a direct path read wait. Can you show me some doc which expalain this in more detail than Oracle doc? Thanks in advance.

Hmm....ok, well,first, there's a problem w/ the hint specification.
The USE_HASH hint makes no sense as a hint to the insert statement. It only makes sense in the context of a select statement. Also, it should specify a table alias. So, you could have something like:
insert /*+ APPEND */.into some_tab
select /*+ use_hash(tab_alias) */ col1,col2,col3 from .....
Now, as to the question of direct path read:
The direct path read event indicates a disk sort. So, it's likely the source of the direct path read wait was due to sorting in the processing of the select statement. I can't imagine how the insert would cause direct path read.
Hope that helps,
-Mark

Direct Path Insert on Forms

Hi,
I am using following insert statement on my forms application to do direct path insert.
insert into /*+append*/ abc select * from xyz;
as redo is not generated if you do direct path insert but in above case redo is generating for the above insert statement.
I then created a procedure test_insert as below
create procedure test_insert is
begin
insert into /*+append*/ abc select * from xyz;
end;
i then replaced the insert statement with above procedure on form and after that redo for the insert statement stopped.
i was wondering if we could use append hint for direct path insert on forms?

My point, though, is that if you're doing your hourly load into a separate table and building the index(es) on that table before moving the partition into the partitioned table, there is no risk of doing anything to screw up the partitioned table. It's also a very handy way to ensure that your load process doesn't interfere with your production data.
If i have understood your point right, what about the space required ( tablespaces and the indexes). Trust me, my table at source gets populated @ over 230 MIL records /day. If i have a temp table, i will have to maintain hourly partitions/indexes/tablespaces for the temp table to hold so much data, isn't it? And, the data i move (say today's data) will be used by the user only after 4 days (because it is available in the source). We have provisioned our user interface to connect to 2 databases, one with 5 days of data (incl. sysdate) and the other one is a archive DB that holds 45 days worth of data.
</>
I wouldn't expect that a direct path load into a single partition of a partitioned table would invalidate local indexes on other partitions, but since I'd never do a direct path load into a single partition of a partitioned table, I've not tested this to make sure.
No problem, if i try this out i will share it in the forum. </>Thanks

How can I tell if direct-path insert is really being used?

I have a number of INSERT statements with /*+ APPEND */ hints, that I suspect are not using direct-path insert processing. How can I tell (via the plan, via Enterprise Manager, whatever) if direct-path is being used?
If it is not being used, then I can research why that might be, and try to resolve the obstacles there. But if it is being used, then I want to know that so I can focus elsewhere.
Thanks,
Mike

mtefft wrote:
The question of whether direct-path is possible with multi-table inserts has been on my mind...
Moreover, in another forum post, we have eyewitnesses that it has happened at least once:
APPEND Hint in Multi-table insert
So I think that post (giving examples of Explain plans with multi-table inserts successfully using direct-path) answers my question.
Mike,
Thanks for that link. When I checked my example again I realised that it had a foreign key constraint between the two tables I was inserting into. (It was a demonstration of how to normalise an incoming denormalised address table, so converted a flat table into address/address lines). When I removed the constraint I got the multi-table insert.
However, I followed this up with a check on the execution plans and for the 10.2.0.3 I was running noted the following:
Plan reported after running the insert and select from dbms_xplan.display_cursor()
| Id | Operation           | Name | Rows | Bytes | Cost |
|   0 | INSERT STATEMENT    |      |       |       |    30 |
|   1 | MULTI-TABLE INSERT |      |       |       |       |
|   2 |   TABLE ACCESS FULL | T3   | 10000 | 1240K|    30 |
------------------------------------------------------------Plan reported after explain plan / select from dbms_xplan.display()
| Id | Operation           | Name | Rows | Bytes | Cost |
|   0 | INSERT STATEMENT    |      | 10000 | 1240K|    30 |
|   1 | MULTI-TABLE INSERT |      |       |       |       |
|   2 |   DIRECT LOAD INTO | T1   |       |       |       |
|   3 |   DIRECT LOAD INTO | T2   |       |       |       |
|   4 |    TABLE ACCESS FULL| T3   | 10000 | 1240K|    30 |
------------------------------------------------------------If you try to check for direct path inserts by looking at the in-memory plans, you might not see the direct load that is really happening. (Perhaps the a check that both / all the target tables are locked with TM mode 6 may give you a clue.)
Regards
Jonathan Lewis

Nologging direct-path insert into an indexed table

Hello,
Does anyone have an idea how I can suppress generation of undo logs for direct-path insert into an indexed table on 11.2.0.1.0:
CREATE TABLE TBL(ID NUMBER) NOLOGGING;
CREATE INDEX IDX ON TBL(ID) NOLOGGING;
INSERT /*+ APPEND */ INTO TBL SELECT /*+ APPEND */ ROWNUM FROM ...; -- Source table has 400,000,000+ rows
Regards,
Angel Tsankov

Pl do not post duplicates - Why does Oracle not use direct-path insert when instructed to do so - pl continue the discussion in your original thread

Direct load insert vs direct path insert vs nologging

Hello. I am trying to load data from table A(only 4 columns) to table B. Table B is new. I have 25 million records in table A. I have debating between direct load insert,, direct path insert and nologging. What is the diference between the three methods of data load? What is the best approach??

Hello,
The fastest way to move data from Table A to Table B is by using direct path insert with no-logging option turned on table B. Meaning this will be produce minimum logging and in case of DR you might not be able to recover data in table B. Now Direct path insert is equivalence of loading data from flat using direct load method. Generally using conventional method it's six phases to move your data from source (table, flat file) to target (table). But with direct path/load it will cut down to 3, and if in addition you will use PARALLEL hint on select and insert you might have faster result.
INSERT /*+ APPEND */ INTO TABLE_B SELECT * from TABLE_A;Regards
Correction to select statement
Edited by: OrionNet on Feb 19, 2009 11:28 PM

Direct Path Insert into temporary table

Hi,
I made the following experiment (temp_idtable is a temp table with a single column id, V_PstSigLink is a complex View):
14:24:28 SQL> insert into temp_idtable select id from V_PstSigLink;
17084 Zeilen wurden erstellt. (in english: rows inswerted)
Statistiken
24 recursive calls
52718 db block gets
38305 consistent gets
16 physical reads
4860544 redo size
629 bytes sent via SQL*Net to client
553 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
4 sorts (memory)
0 sorts (disk)
17084 rows processed
14:24:41 SQL> commit;
Transaktion mit COMMIT abgeschlossen.
14:25:29 SQL> insert /*+ APPEND*/into temp_idtable select id from V_PstSigLink;
17084 Zeilen wurden erstellt. (in english: rows inswerted)
Statistiken
1778 recursive calls
775 db block gets
38847 consistent gets
40 physical reads
427408 redo size
613 bytes sent via SQL*Net to client
565 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
27 sorts (memory)
0 sorts (disk)
17084 rows processed
As you can see, with /*+ APPEND*/ there will be much less REDO generated.
How can it be?
1. /*+ APPEND*/ only doesn't mean that there shouldn't be REDO generated, does it? For that one has to declare the table with NOLOGGING.
2. In the doc there is a statement that for temp. tables there is no REDO log generated, just UNDO (and REDO only for UNDO).
Where is the difference coming from?
If I use Direct Path (APPEND) for a temp table, where will be the table populated - in the Buufer Cache or directly in a temporary segment on the disk?
Balazs

Hi John,
I'm a little confused about your statement " Oracle does not cache data blocks until they are read from a table.". I wanted to make a little experiment with KEEP Buffer Cache to see weather I can 'pin' the content of a temp table. But before getting to pin I realized an interesting behavior. Please see this sqlplus log:
SQL> create global temporary table temp_ins(id NUMBER);
Table created.
SQL> insert into temp_ins values (1);
1 row created.
SQL> insert into temp_ins values (2);
1 row created.
SQL> insert into temp_ins values (3);
1 row created.
SQL> set autotrace on explain statistics;
SQL> select * from temp_ins;
ID
1
2
3
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 TABLE ACCESS (FULL) OF 'TEMP_INS'
Statistics
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
416 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
3 rows processed
SQL>
I realized exectly the opposit of your statement! Oracle apparently cached the content of the temp table before it read from it!! Could you please explain why? Now I'm going to try it with a normal table...
Balazs

Direct-Path Inserts

If the data bypasses the buffer cache and is written to the data files directly, does that mean the insert commits implicitly? Also, would it be safe to say that this would be a means of doing an insert without having to drop or disable constraints?
Matt

There is no implicit commit done.
http://download.oracle.com/docs/cd/B28359_01/server.111/b28286/statements_9014.htm#SQLRF01604
Will show you the restrictions, most notable (for your question).
"The target table cannot have any triggers or referential integrity constraints defined on it."

Direct-Path with (No)Archivelog and recovery

Hi,
In a datawarehouse environment, our database is in NOARCHIVELOG. When we do a Insert /*+ APPEND */ on a table withLOGGING attribute, a miniminal redo log is generated.
We want to switch the database in ARCHIVELOG mode, and change the attribute of the table to NOLOGGING .
My question is, does instance recovery will work ?
I made a matrix of the effect of a crash while a direct-path Insert operation :
Database mode                   Table mode               Instance recovery                      Media recovery
NOARCHIVELOG                     LOGGING                        OK                                     NOT OK
ARCHIVELOG                       LOGGING                        OK                                     OK
ARCHIVELOG                       NOLOGGING                      OK                                     NOT OK
Do you agree with this matrix ?
Regards

Yes instance recovery will work regardless of direct-path and nologgging usage.
Here is an example with Oracle XE on Windows (database runs in ARCHIVELOG mode and FORCE_LOGGING is not set):
c:\tmp>rman target /
Recovery Manager: Release 11.2.0.2.0 - Production on Jeu. Janv. 12 20:05:32 2012
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
connected to target database: XE (DBID=2642463371)
RMAN> report unrecoverable;
using target database control file instead of recovery catalog
Report of files that need backup due to unrecoverable operations
File Type of Backup Required Name
RMAN> exit
Recovery Manager complete.
c:\tmp>sqlplus xxx/xxx @nolog.sql
SQL*Plus: Release 11.2.0.2.0 Production on Jeu. Janv. 12 20:05:48 2012
Copyright (c) 1982, 2010, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - Production
SQL> select log_mode, force_logging from v$database;
LOG_MODE     FOR
ARCHIVELOG   NO
SQL> drop table tnl purge;
Table dropped.
SQL> create table tnl(x int) nologging tablespace users;
Table created.
SQL> insert /*+ APPEND */ into tnl select object_id from all_objects;
17971 rows created.
SQL> commit;
Commit complete.
SQL> connect / as sysdba
Connected.
SQL> startup force
ORACLE instance started.
Total System Global Area 1071333376 bytes
Fixed Size                  1388352 bytes
Variable Size             658505920 bytes
Database Buffers          406847488 bytes
Redo Buffers                4591616 bytes
Database mounted.
Database opened.
SQL> exit
Disconnected from Oracle Database 11g Express Edition Release 11.2.0.2.0 - Production
c:\tmp>rman target /
Recovery Manager: Release 11.2.0.2.0 - Production on Jeu. Janv. 12 20:07:34 2012
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
connected to target database: XE (DBID=2642463371)
RMAN> report unrecoverable;
using target database control file instead of recovery catalog
Report of files that need backup due to unrecoverable operations
File Type of Backup Required Name
4    full or incremental     C:\ORACLEXE\APP\ORACLE\ORADATA\XE\USERS.DBF
RMAN> exit
Recovery Manager complete.
c:\tmp>Edited by: P. Forstmann on 12 janv. 2012 20:08

Regarding Direct Load or Direct Path Load

Why Direct Load and Direct Path Load is faster?
In which situation Direct Load, Direct Path Load are faster?

>
Why Direct Load and Direct Path Load is faster?
In which situation Direct Load, Direct Path Load are faster?
>
See About Direct-Path INSERT in the DBA doc
http://docs.oracle.com/cd/E11882_01/server.112/e17120/tables004.htm#i1009100
>
About Direct-Path INSERT
Oracle Database inserts data into a table in one of two ways:
•During conventional INSERT operations, the database reuses free space in the table, interleaving newly inserted data with existing data. During such operations, the database also maintains referential integrity constraints.
•During direct-path INSERT operations, the database appends the inserted data after existing data in the table. Data is written directly into datafiles, bypassing the buffer cache. Free space in the table is not reused, and referential integrity constraints are ignored. Direct-path INSERT can perform significantly better than conventional insert.

APPEND (direct path) - redo size

I am sure, I might be missing something obvious. I am under the impression that DIRECT PATH loads (such as inserts with APPEND hint )would generate less redo. But, not sure why I am seeing this...
Regular Insert (Not direct path):
====================
SQL> insert into c2 Select * from dba_objects where rownum < 301;
300 rows created.
Statistics
10 recursive calls
74 db block gets
353 consistent gets
1 physical reads
*31044 redo size*
821 bytes sent via SQL*Net to client
752 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
300 rows processed
Direct Path Insert
===========
SQL> insert /*+ APPEND */ into c2 Select * from dba_objects where rownum < 301;
300 rows created.
Statistics
8 recursive calls
13 db block gets
346 consistent gets
1 physical reads
*39048 redo size*
809 bytes sent via SQL*Net to client
770 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
300 rows processed
Not sure, why am I seeing more redo being generated with DIRECT PATH .... either I am missing something obvious or got the DIRECT PATH load completely wrong...would really appreciate any help with this.

Hello,
Check out this thread:
[http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:3224814814761]
Additionally, if you were to switch off logging at the table level, before the INSERT, you should see a (further) reduction in redo:
ALTER TABLE your_table NOLOGGING;

Direct Path Inserts = By DBWR or by Shadow Process

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