Informatica Bulk Mode behavior 2004-04-27 - By Khedr, Waleed
We use high setting for the commit interval (hundred million) without =
problems.
The error ORA-01658 (See ORA-01658.ora-code.com) they are talking about, does not make sense.
Waleed
-- --Original Message-- --
From: Thomas Jeff [mailto:jeff.thomas@(protected)]
Sent: Tuesday, April 27, 2004 8:53 AM
To: oracle-l@(protected)
Subject: RE: Informatica Bulk Mode behavior
Tim, Waleed, we got this response from Informatica Support:
We are using the OCI DPL (direct path load) in the following way:
First, We get a block with "x " # of rows.
Do following loop
Call ColArrayToStream for these "x " rows.
Load whatever we can (call DirPathLoadStream)
Do a DirPathStreamReset.
while ColArrayToStream did not convert all the rows, repeat the above
steps for the remainder rows.
Every so often, depending on our "commit " interval, we will call
DirPathFinish (and then reprepare).
The 2 differences between our process and Oracle 's demo program are:
1) the # of rows "x " may be different. They may be optimizing the "x "
that they pick. We derive "x "=3D20
from the buffer block size.
2) Oracle does 1 DirPathFinish at the end of the process, whereas we do
it on every commit. =3D20
Thus, we could probably simulate exactly what Oracle 's test program is
doing by making sure that the=3D20
# of rows in the block matches their test program and the target commit
interval is really high.
So there seem to be 2 possible places where we may be causing more
extents to be created than necessary. =3D20
1) The last load in the loop may be less than the amount of rows that
can fit in a transfer block. Not sure if this matters at all, but if
the last load contains only 1 row, this may be a wasted allocated
extent.
2) The DirPathFinish DEFINITELY seems to be causing a new extent to be
created.
We still have one X factor that we need to account for. The CR mentions
that if the commit interval is high, we=3D20
sometimes get the following error:
ORA-01658 (See ORA-01658.ora-code.com): unable to create INITIAL extent for segment in table =
space=3D20
Our guess is that somehow we ran out of space to get an extent.
(perhaps in the temp table space) Perhaps=3D20
this can be limited somehow if there is a way to turn off logging (if it
was, indeed, on), but I didn 't see=3D20
this option available. Although we haven 't tested this yet, we would
think that the sample program would have=3D20
similar issues, although it may take a little longer because they may
not have wasted extents as listed in option=3D20
1) above.
Solutions:
The workaround fix is to play with the buffer block size and the commit
size. If the buffer block size fits=3D20
the correct amount of rows, we may have a somewhat optimal fix. We may
want to consider logging certain=3D20
information that may help the user pick a correct buffer size, but, of
course, this can be kinda cryptic.
-- --Original Message-- --
From: oracle-l-bounce@(protected)
[mailto:oracle-l-bounce@(protected)] On Behalf Of Khedr, Waleed
Sent: Tuesday, April 27, 2004 12:17 AM
To: oracle-l@(protected)
Subject: RE: Informatica Bulk Mode behavior
I use Informatica 6.x and so far did not have any problem.
But you may be right, that this might have to do with the way =3D3D
Informatica calls Oracle OCI.
The other way I see it, Informatica is giving bulk load as a relational
=3D3D method to load the target instead of external loader, which must =
be =3D
=3D3D
thread-safe to run without problems using their multi-thread options. =
=3D
=3D3D
This leads to the issues we encountered when we run direct load in =3D3D
parallel, which is different than parallel DML/insert in direct mode =
=3D3D
where threads try to broker the HWM.
Regards,
Waleed
-- --Original Message-- --
From: Tim Gorman [mailto:tim@(protected)]
Sent: Monday, April 26, 2004 3:16 PM
To: oracle-l@(protected)
Subject: Re: Informatica Bulk Mode behavior
Jeff and Waleed,
I think Informatica is blowing smoke on this error message, or at least
=3D3D they are smoking something...
Each time you initiate a direct-path load operation, it will allocate a
=3D3D new extent, but the arraysize or data save frequency has no =
bearing =3D
on
size =3D3D or number of extents, whether using "direct-path " (a.k.a. =3D
"bulk ")
loads or "conventional " SQL INSERT loads. In other words, based on the
behavior described, it is quite likely that Informatica has a bug in
their =3D3D bulk-load functionality resulting from improper use of the
Oracle Call Interface =3D3D
(OCI)
application programming interface (API). I don 't think that the cause =
=3D
=3D3D
of the ORA-01658 (See ORA-01658.ora-code.com) error has to do with a problem of any kind within
Oracle =3D3D at all, no matter whose perspective you use.
Programs like Informatica can only use the OCI functions for direct-path
loading (i.e. Functions named "OCIDirPath...() ") and none of these OCI
functions presents any controls for extent sizing.
The only explanation is that Informatica is doing something silly and
pointless like calling "OCIDirPathFinish() " instead of
"OCIDirPathDataSave() " after each data save.
The "OCIDirPathFinish() " function closes a direct-path load session,
requiring that a new direct-path load session be initiated, causing a =
=3D
=3D3D
new extent to be allocated. The "OCIDirPathDataSave() " function merely
=3D3D saves the rows to blocks on disk, but does not initiate a new =
extent
or have =3D3D any control over extents.
In which case, the Informatica documentation should read something like:
Informatica code bug: Due to a misreading of Oracle 's documentation
and sample OCI code, Informatica is improperly performing data
saves during bulk loads using the "direct-path " API.
Solution: Set the commit interval very high, to mask the fact that
Informatica is improperly ending the direct-path load with each
data save. This will result in fewer extents being used and
less space being wasted, depending on the table 's extent size.
Just my $0.02 as a long-time OCI programmer. I don 't know for sure if =
=3D
=3D3D
this is what is happening, but it sure as heck sounds like it. It would
be interesting to "truss " the Informatica load process, to see what OCI
function calls it is issuing... :-)
Hope this helps...
-Tim
P.S. It would be interesting to find out if Informatica v7.x
includes any "performance enhancements " for bulk loading
over v6.x. If so, the only "enhancement " I can think of is
that they detected their own bug and fixed it... :-)
After all, nothing new has been added to the "OCIDirPath...() "
functions in the way of a performance enhancement since they
became available in v8.0.x, I 'm pretty sure...
on 4/26/04 6:48 AM, Thomas Jeff at jeff.thomas@(protected) wrote:
> Waleed, =3D3D3D20
>=3D3D20
> Indeed you were on the right track. We got the following msg from
> Informatica
> Support. "Oracle design limitation "?????? =3D3D3D20
>=3D3D20
>=3D3D20
> Problem:
>=3D3D20
> In 6.x version running session targeting to Oracle using bulk mode =
=3D20
>creates new extents=3D3D3D20 at every commit. This sometimes leads to =
=3D
the=3D20
>following error: =3D3D
"ORA-01568 (See ORA-01568.ora-code.com)
> unable to create=3D3D3D20
> initial extent. "=3D3D3D20
>=3D3D20
> Solution:
>=3D3D20
> This is a known issue (CR 53791) that occurs when using Oracle bulk =
=3D20
>loading. To resolve this=3D3D3D20 issue increase the commit interval =
to=3D20
>very high value. SUPPORTING
> INFORMATION: This issue is=3D3D3D20
> due to the following design limitation in Oracle: Direct Path Loading
>(using same code as bulk=3D3D3D20
> loading) is going to use only blocks above the high water mark. Also =
=3D20
>Direct Path loading does=3D3D3D20 not check for Partial blocks are =
not=3D20
>used, so no reads are needed to find them and fewer writes=3D3D3D20
> are performed. In a conventional data load the bind array buffer is
> filled and passed to Oracle=3D3D3D20
> with a SQL INSERT command which results in the space management by the
> SQL Command Processing to=3D3D3D20
> be utilized. Therefore bulk loading will allocate more =
extents.=3D3D3D20
>=3D3D20
>=3D3D20
> -- --Original Message-- --
> From: oracle-l-bounce@(protected)
> [mailto:oracle-l-bounce@(protected)] On Behalf Of Khedr, Waleed
> Sent: Thursday, April 22, 2004 11:34 AM
> To: oracle-l@(protected)
> Subject: RE: Informatica Bulk Mode behavior
>=3D3D20
>=3D3D20
> I would ask the developers how they configured the commit interval (if
=3D3D
=3D3D3D
> =3D3D3D3D
> it 's set to a very low value)
>=3D3D20
> Waleed
>=3D3D20
> -- --Original Message-- --
> From: Thomas Jeff [mailto:jeff.thomas@(protected)]
> Sent: Thursday, April 22, 2004 10:33 AM
> To: oracle-l@(protected)
> Subject: Informatica Bulk Mode behavior
>=3D3D20
>=3D3D20
> List,
> Is anyone familiar with how Informatica 's bulk mode works? =
=3D3D3D3D20=3D20
>=3D3D20 We have a situation where I created a 4GB tablespace for a new =
=3D
and
> simple=3D3D3D3D20 truncate/load operation from Informatica, around 7 =
=3D3D
million
> rows estimated=3D3D3D3D20 to take up 1.5GB. =3D3D3D3D20 =3D3D3D3D20 =
Using =3D
bulk =3D3D
mode, =3D3D3D
> which
> appears to be a direct load (in the SQL cache, the=3D3D3D3D20 INSERT =
=3D3D
statement
> has a hint that I 've never seen before: SYS_DL_CURSOR =
which=3D3D3D3D20 =3D
I=3D20
> =3D3D
=3D3D3D
> assume
> stands for Direct Load), they run out of space in the tablespace =3D20
>after=3D3D3D3D20 about 200K rows have been inserted. =3D3D20
> If I then manually rebuild the table, the 200K rows gets compressed =
=3D
=3D3D
back
> down=3D3D3D3D20 to one extent.
>=3D3D20
> So there 's a lot of either empty or preallocated space. Thinking
> somehow=3D3D3D3D20
> the high-water mark was the culprit, I manually truncated the table =
=3D20
>before=3D3D3D3D20 they reran their job. =3D3D3D3D20 =3D3D20
> Still the same problem. =3D3D3D3D20
>=3D3D20
> If the job runs in 'normal ' mode, which is row-by-row processing, it
> runs fine,=3D3D3D3D20 although of course, performance is quite poor.
>=3D3D20
> Any ideas/experience as to how this bulk mode operates?
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