MSSQL Query Memory when using long fields

Here is our problem...

We are doing a lot of selects against a table that has one large field
in it.

If we do a select against all the fields except for description, the
query comes back relatively quickly. If we add that last field (768
chars) to the query, our query takes 10x longer (5 seconds vs 56
seconds.)

When we run the one without the description column, we can watch
perfmon and see a very quick spike to physical disk. If we add in the
description field we can see that the server becomes I/O bound - the
disk sits at 100% until the query is complete.

We have tweaked the min query memory setting for the server but it
seems to have had no effect no matter how high we set it. Is there
some point at which MSSQL decides it cannot perform the transaction in
memory? What would I increase to cure this problem?

For example:
TMZDIFF int410
WRITETIMEcharno 16
System_Namecharno 64
Timestampcharno16
Name charno32
Mount_Pointcharno32
Size intno4 10
Space_Usedintno410
Space_Availableintno410
Inode_Sizeintno410
Inodes_Usedintno410
Inodes_Freeintno410
Space_Used_Percentintno410
Inodes_Used_Percentintno410
FS_Type charno8
Space_Available_Percentintno410
Name_U ncharno32
Descriptionncharno768(wildfyre53207@.yahoo.com) writes:
> If we do a select against all the fields except for description, the
> query comes back relatively quickly. If we add that last field (768
> chars) to the query, our query takes 10x longer (5 seconds vs 56
> seconds.)

My initial reaction is that there is an index on the table that covers
all columns, save the long column.

Could you post CREATE TABLE and CREATE INDEX statements for the table?
Don't forget PRIMARY KEY and UNIQUE constraints.

> We have tweaked the min query memory setting for the server but it
> seems to have had no effect no matter how high we set it. Is there
> some point at which MSSQL decides it cannot perform the transaction in
> memory? What would I increase to cure this problem?

How many rows are you returning? On what sort of network connection?
How much memory do you have in the machine?

--
Erland Sommarskog, SQL Server MVP, esquel@.sommarskog.se

Books Online for SQL Server 2005 at
http://www.microsoft.com/technet/pr...oads/books.mspx
Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodin...ions/books.mspx|||give us an example of the two selects.