Posted by wildfyre53207 on 03/02/06 17:50

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 int 4 10
WRITETIME char no 16
System_Name char no 64
Timestamp char no 16
Name char no 32
Mount_Point char no 32
Size int no 4 10
Space_Used int no 4 10
Space_Available int no 4 10
Inode_Size int no 4 10
Inodes_Used int no 4 10
Inodes_Free int no 4 10
Space_Used_Percent int no 4 10
Inodes_Used_Percent int no 4 10
FS_Type char no 8
Space_Available_Percent int no 4 10
Name_U nchar no 32
Description nchar no 768

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