Re: Tables with VARCHAR

Yep...it depends...

what's "pretty large char fields"?  The entire record is only 650
bytes...so they can't be all that large to my way of thinking..

What's "almost empty"?

run a
select length(trim(MYFLD)), count(*) as cnt
from myfile
group by  length(trim(MYFLD))
order by 2 desc

If the field is CHAR(100) and most of the records have 20 chars or less...

Then you might be better off with VARCHAR(100) ALLOCATE (20)

That'd save 78 bytes for every record with less than 20 chars.

However, one additional point to consider.  Are you using SQL or record
level access (RLA)?

With RLA, the system will do two disk I/Os for every record with more than
20 chars.  With SQL, those 2 I/Os will only be done if you ask for MYFLD to
be returned.

(Thus the reason ALLOCATE(0) is not recommended, unless most records are
empty)

Charles


On Wed, Apr 4, 2018 at 8:30 AM, Jon Paris <[email protected]> wrote:

> As is often the case - it depends.
>
> When you define a field as Varchar you can specify both a "normal" length
> and a maximum length.  Only the "normal" part is held with the main record
> and therefore if most of your records are within that length then the file
> size will reduce.
>
> There is however an overhead for linking to the extended space - can't
> recall how long it is 20 bytes is ringing a faint bell.  This topic has
> been discussed in the past on the Midrange list - I'd check it for you but
> have to run out.
>
>
> Jon Paris
>
> www.partner400.com
> www.SystemiDeveloper.com
>
> > On Apr 4, 2018, at 10:05 AM, Jevgeni Astanovski <[email protected]>
> wrote:
> >
> > Hi,
> > Does anyone here know if switching from CHAR to VARCHAR gives any
> positive
> > effect in terms of table size?
> > Explain the situation briefly.
> > I've got an application written on ILE/C that works with rather big table
> > (historical data since 1996). Currently the table size is 260M records
> and
> > PF size 170GB.
> > The record size is app. 650 bytes and it has some pretty large char
> fields,
> > that can be either empty or almost empty :-)
> >
> > Technically I can make a new table with VARCHARs and rewrite my program
> to
> > use VARCHAR instead of CHAR, but shall it reduce the table size?
> >
> > Somehow I suspect that it will only increase the table...
> >
> > TIA and regards,
> > Jevgeni.
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