so I keep optimizing my fields down to the minimum character length
necessary i.e., varchar(15), then I find out a month later its gotta
get bigger, then a few months later, bigger again, etc.  Nowadays on
sql server 2005 and on, how bad is it really to use varchar(max)?  Is
there really a big performance or storage hit or is it negligible?

-Mike

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mike wrote:
> so I keep optimizing my fields down to the minimum character length
> necessary i.e., varchar(15), then I find out a month later its gotta
> get bigger, then a few months later, bigger again, etc.  Nowadays on
> sql server 2005 and on, how bad is it really to use varchar(max)?  Is
> there really a big performance or storage hit or is it negligible?
>
> -Mike

Don't be lazy. There are several reasons for not doing this in the
comments for this blog article:
http://sqljunkies.com/WebLog/simons... />
r_max.aspx
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"Bob Barrows [MVP]" <reb01501@NOyahoo.SPAMcom> wrote in message
news:ugOP4gmaHHA.4616@TK2MSFTNGP03.phx.gbl...
> mike wrote: 
>
> Don't be lazy. There are several reasons for not doing this in the
> comments for this blog article:
>
http://sqljunkies.com/WebLog/simons... />
r_max.aspx


Hmm.. Interesting. I'm not sure some of the commenters were making a
distinction between varchar(somevalue) and varchar(max)?  They seemed to be
comparing varchar with char.  Others were concerned unexpected growth but if
there is a cause for that in the lifetime of a DB then the alternative is
errors downstream where data entered doesn't fit in the defined field.
Personally I'd rather see things slow down instead of break.

I agree it does seem a bit lazy though.

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Anthony Jones wrote:
> "Bob Barrows [MVP]" <reb01501@NOyahoo.SPAMcom> wrote in message
> news:ugOP4gmaHHA.4616@TK2MSFTNGP03.phx.gbl... 
> http://sqljunkies.com/WebLog/simons...>
har_max.aspx
>
>
> Hmm.. Interesting. I'm not sure some of the commenters were making a
> distinction between varchar(somevalue) and varchar(max)?

I'm not sure what you were looking at. all the comments seemed to be on
target.

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"Bob Barrows [MVP]" <reb01501@NOyahoo.SPAMcom> wrote in message
news:%23B3LVLoaHHA.4856@TK2MSFTNGP03.phx.gbl...
> Anthony Jones wrote: 
http://sqljunkies.com/WebLog/simons...archar_max.aspx
[vbcol=seagreen] 
>
> I'm not sure what you were looking at. all the comments seemed to be on
> target.
>

The final comment by werner de jong seems to be entirely based on the
difference between char and varchar.

Also others references performance issues.  I'm wondering where there is a
cost in performance between varchar(x)  and varchar(max)?

Could be that I'm ignorant of some new details of 2005 internals.  What is
the difference internally in the way these fields are handled.

Belsteak says 'unpredictable growth of the DB' and 'unwanted results in
column', what does that mean??

Anthony.

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Anthony Jones wrote: 
>
> The final comment by werner de jong seems to be entirely based on the
> difference between char and varchar.

No, I believe he was talking about the impact of having many varchar columns
as opposed to a few. He is likely assuming that at least some of the
varchar(max) columns could be char, since the blog post he was replying to
made no reference to leaving existing char columns alone. Or using
varchar(max) to store other data types.

>
> Also others references performance issues.  I'm wondering where there
> is a
> cost in performance between varchar(x)  and varchar(max)?

I think Adam Machanic's article covers this: "Remember that the query
optimizer uses column size as one of the many metrics for determining
optimal query plans. Given this table, the optimizer would have very few
options in that regard. "

>
> Could be that I'm ignorant of some new details of 2005 internals.
> What is
> the difference internally in the way these fields are handled.
>

Again, from Adam's article:
The MAX data types, by default, use a hybrid of the TEXT/IMAGE overflow
behavior and the behavior of the normal (sized) VARCHAR/VARBINARY types. If
a column's data, plus the data in all of the other columns in the table, has
a total size of less than 8060 bytes, the data is stored in-row. If the data
exceeds 8060 bytes, the data in the MAX column will be stored off-row.

> Belsteak says 'unpredictable growth of the DB' and 'unwanted results
> in
> column', what does that mean??
>

With varchar(max) one cannot be sure how much data is going to be stored in
it.  Thus database growth cannot be predicted, making any forecasts of
database size meaningless. Also, every time a record's size exceeds a page
(8000 b), the record gets split. Every time the split occurs, performance
suffers, both for maintaining and for reading the data. Since we are not
controlling how much data gets stored, we cannot predict how many splits
will occur. "Unwanted results" I believe is referring to the lack of control
of data size removing one key validation method for preventing unwanted
data.

Many of these arguments are the same ones used to counter the old "why not
make every column a varchar(8000) column" proposal in the SQL2000 days.


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"Bob Barrows [MVP]" <reb01501@NOyahoo.SPAMcom> wrote in message
news:O98pDGuaHHA.4808@TK2MSFTNGP04.phx.gbl...
> Anthony Jones wrote: 
>
> No, I believe he was talking about the impact of having many varchar
columns
> as opposed to a few. He is likely assuming that at least some of the
> varchar(max) columns could be char, since the blog post he was replying to
> made no reference to leaving existing char columns alone. Or using
> varchar(max) to store other data types.

I see.  I didn't read it that way.  It seems to me the blogger is talking
about varchar(n) vs varchar(max).

> 
>
> I think Adam Machanic's article covers this: "Remember that the query
> optimizer uses column size as one of the many metrics for determining
> optimal query plans. Given this table, the optimizer would have very few
> options in that regard. "

That's a good point.  Statistics are not by default built for varchar(max)
fields but I believe they can be specified.

> 
>
> Again, from Adam's article:
> The MAX data types, by default, use a hybrid of the TEXT/IMAGE overflow
> behavior and the behavior of the normal (sized) VARCHAR/VARBINARY types.
If
> a column's data, plus the data in all of the other columns in the table,
has
> a total size of less than 8060 bytes, the data is stored in-row. If the
data
> exceeds 8060 bytes, the data in the MAX column will be stored off-row.

Cool.  A pragmatic solution. I like.

> 
>
> With varchar(max) one cannot be sure how much data is going to be stored
in
> it.  Thus database growth cannot be predicted, making any forecasts of
> database size meaningless.

Using varchar(max) doesn't mean you haven't got a reasonable idea of the
size of data going into the field. It means you don't want to limit the size
that might end up in there.   I'm being devils adovacate here, for small
fields, titles, descriptions, names etc I wouldn't use varchar(max) either
(I agreed it is lazy) but for anything over say 512 I would have been
tempted but:-

> Also, every time a record's size exceeds a page
> (8000 b), the record gets split. Every time the split occurs, performance
> suffers, both for maintaining and for reading the data. Since we are not
> controlling how much data gets stored, we cannot predict how many splits
> will occur.

Ouch.  Yes that's a killer reason.

> "Unwanted results" I believe is referring to the lack of control
> of data size removing one key validation method for preventing unwanted
> data.

Good point.

>
> Many of these arguments are the same ones used to counter the old "why not
> make every column a varchar(8000) column" proposal in the SQL2000 days.
>
>
> --
> Microsoft MVP - ASP/ASP.NET
> Please reply to the newsgroup. This email account is my spam trap so I
> don't check it very often. If you must reply off-line, then remove the
> "NO SPAM"
>
>

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