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Home -> Community -> Usenet -> c.d.o.misc -> Re: Max lenght of primary key ??
Bas Ven wrote:
>
> Excuse my ignorance, but what is an 'oracle7 block size' ?
> It seems quite a strange restriction that (in my case) I
> can't create a key with a length >= 750 bytes.
>
> Brian P. Mac Lean wrote:
> >
> > The Oracle7 Server Reference, Version 7.2, Chapter 5, Page 2/3:
> >
> > Item Type Limit
> >
> > columns index (or 16 columns maximum
> > cluster index)
> >
> > indexes table no limit
> >
> > total size of one-half the Oracle7 block size minus some overhead
> > indexed columns
> >
> > -----
The database block size can be found with the following query:
select * from v$parameter where name = 'db_block_size';
The Oracle7 Server Reference Manual describes db_block_size as:
DB_BLOCK_SIZE Default value: operating system-dependent Range of values: operating system-dependent (1024 - 8192) Multiple instances: must have the same value
The size in bytes of Oracle database blocks. Typical values are
2048 and 4096. The value for
DB_BLOCK_SIZE in effect at CREATE DATABASE time determines the size of
the blocks; at all
other times the value must be set to the original value.
This parameter affects the maximum value of the FREELISTS storage
parameter for tables and
indexes.
For more information block size, see Oracle7 Server Concepts.
See also your operating system-specific Oracle documentation for
the default value.
If you are not familiar with database blocks/db_block_size, it's time to
do some reading.
It is the basis of all storage in the database. Tables, indexes, sga.
Almost everything is
effected by it.
Learn it, know it, live it.
mailto:brian.maclean_at_teldta.com
"We trained hard, but it seemed that every time we were beginning to
form into teams
we would be reorganized. I was to learn later in life that we tend to
meet any new
sitiation by reorganizing, and what a wonderful method it can be for
creating the
illusion of progress while producing confusion, inefficiency, and
demoralization."
Petronius Arbiter 210 B.C. Received on Tue Jun 24 1997 - 00:00:00 CDT
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