Hi Tim,
Thanks for that, but i think i do not explain myself properly.
They are using varchar2 (4000) on the varchar2 columns.
On the other columns they are using what they need (date,
timestamp,clob, etc,etc), so in this case the datatype conversion does
not concern me really.
There are just using 4000 for a simple code description (AA, AB, etc)
just in case this code description increases in future. Now apply this
to all varchar2 on all the tables.
Hope is more clear now J
Anyway thanks again for your reply.
Regards
*From:*oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *Tim Gorman
*Sent:* 22 December 2014 16:06
*To:* oracle-l@xxxxxxxxxxxxx
*Subject:* Re: DWH varchar2(4000)
Richard,
Space is not an issue; a VARCHAR2 uses only as much storage as needed
for the data. The precision of 4000 is only a constraint for stored
values and a hint to display programs; it is not like the right-padded
CHAR datatype.
What is the issue is datatype conversion. Besides implicit sorting
semantics for numeric and date/datetime datatypes which will be
eliminated, the Oracle optimizer in particular relies on the semantics
of the datatype to understand data cardinality. For example, two
dates stored as DATE datatypes with values of 28-FEB-2014 and
01-MAR-2014 are known to be "adjacent" values, while values of
28-FEB-2016 and 01-MAR-2016 are known not to be adjacent. This may
not seem like a big deal, but it really is, particularly for DWH
databases which need to make the best decisions possible for an
execution plan for long-running SQL statements.
Oracle is not a NOSQL datastore and not using the appropriate datatype
is tantamount to crippling the Oracle optimizer, which is crucial for
query performance whether they think it is or not.
If the developers/data modelers are pre-provisioning "spare columns"
because they are afraid of running ALTER TABLE ... ADD COLUMN, then
the alternative they have chosen has absolutely zero advantages over
using ALTER TABLE ... ADD COLUMN. Every possible objection they can
dream up is magnified by the course they have chosen. If they simply
don't want to worry about type-conversion, then they simply need to
grow up and realize that data typing is important on this platform,
even if it isn't on other platforms.
Bottom-line: use the correct datatype. If they can't decide, then
they're doing it wrong.
Best of luck!
-Tim
On 12/22/14 8:01, Ricard Martinez wrote:
Hi list,
We have a DWH database on 11.2.0.4.
The developers/data modelers are creating all the tables with
varchar2(4000) as standard by default. They don't care if they
just insert 10 bytes, 200 or nothing.
When asked about why this standard is in place, the answer is
just: "Just in case we need it".
For my point of view this is not a good practice, as can cause
memory waste on client applications, as well as data garbage or
errors like ORA-01450: maximum key length (3218) exceeded.
But as i'm not a DWH expert, maybe im missing information that
proves that this is really a good practice, and not just a
laziness way of working.
I will be glad to know your opinion, or point me to any doc/test
that proves me wrong, in order to learn about this.
Thanks
