Joing tables from different databases - performance issues

Hello,
What is performance difference between joining tables
1. from the same database
2. from different databases located on the same instance of MS SQL Server
3. from different databases located on different instances of MS SQL
Server (linked servers) when these instances are located on the same
physical machine
4. from different databases located on different instances of MS SQL
Server (linked servers) when these instances are located on different
physical machines and these machines contact each other through LAN
I guess, performance or variant 1 is the best and for 4 is the worst,
but if (and how big) are there differences between: 1 and 2, 2 and 3.
Thanks a lot.
MerlinIt is really opene-end question , because only you do know about your tables
structure, indexes and amount of data.
"MerlinXP" <MerlinXP_NOSPAM@.NOSPAM_poczta.onet.pl> wrote in message
news:u5qDn7WAGHA.1032@.TK2MSFTNGP11.phx.gbl...
> Hello,
>
> What is performance difference between joining tables
> 1. from the same database
> 2. from different databases located on the same instance of MS SQL Server
> 3. from different databases located on different instances of MS SQL
> Server (linked servers) when these instances are located on the same
> physical machine
> 4. from different databases located on different instances of MS SQL
> Server (linked servers) when these instances are located on different
> physical machines and these machines contact each other through LAN
> I guess, performance or variant 1 is the best and for 4 is the worst, but
> if (and how big) are there differences between: 1 and 2, 2 and 3.
>
> Thanks a lot.
> Merlin|||1 is same as 2. The optimizer has all the information and can process the qu
ery the same whether the
tables are in the same database or different database. For 3 and 4, the quer
y is optimized locally
and parts of the query is passed onto the linked server. This limits the fle
xibility that the
optimizer otherwise has. 4 is obviously worse than 3. For quantification, yo
u need to test with your
data, schema, queries etc.
Tibor Karaszi, SQL Server MVP
http://www.karaszi.com/sqlserver/default.asp
http://www.solidqualitylearning.com/
Blog: http://solidqualitylearning.com/blogs/tibor/
"MerlinXP" <MerlinXP_NOSPAM@.NOSPAM_poczta.onet.pl> wrote in message
news:u5qDn7WAGHA.1032@.TK2MSFTNGP11.phx.gbl...
> Hello,
>
> What is performance difference between joining tables
> 1. from the same database
> 2. from different databases located on the same instance of MS SQL Server
> 3. from different databases located on different instances of MS SQL Serve
r (linked servers) when
> these instances are located on the same physical machine
> 4. from different databases located on different instances of MS SQL Serve
r (linked servers) when
> these instances are located on different physical machines and these machi
nes contact each other
> through LAN
> I guess, performance or variant 1 is the best and for 4 is the worst, but
if (and how big) are
> there differences between: 1 and 2, 2 and 3.
>
> Thanks a lot.
> Merlin|||
> It is really opene-end question , because only you do know about your tabl
es
> structure, indexes and amount of data.
Structure of these tables is the same in all variants.
I don't expect exact answers, because it is impossible without exact
info, but I think it is possible to point at mainspriongs which affect
performance.
Difference between variants 1 and 4 is obvious.
What about difference between 1 and 2, 2 and 3 it's not obvious for me.
Merlin|||U?ytkownik Tibor Karaszi napisa?:

> 1 is same as 2. The optimizer has all the information and can process
> the query the same whether the tables are in the same database or
> different database. For 3 and 4, the query is optimized locally and
> parts of the query is passed onto the linked server. This limits the
> flexibility that the optimizer otherwise has. 4 is obviously worse than
> 3. For quantification, you need to test with your data, schema, queries
> etc.
Thanks, this is the info what I've expcected.
Do you have feeling what difference can be between variants 2 and 3
(small, medium, big)
Merlin|||> Do you have feeling what difference can be between variants 2 and 3 (small
, medium, big)
I'd say medium to big. But you can always find exceptions.
Tibor Karaszi, SQL Server MVP
http://www.karaszi.com/sqlserver/default.asp
http://www.solidqualitylearning.com/
Blog: http://solidqualitylearning.com/blogs/tibor/
"MerlinXP" <MerlinXP_NOSPAM@.NOSPAM_poczta.onet.pl> wrote in message
news:43A160FA.6060206@.NOSPAM_poczta.onet.pl...
> U?ytkownik Tibor Karaszi napisa?:
>
> Thanks, this is the info what I've expcected.
> Do you have feeling what difference can be between variants 2 and 3 (small
, medium, big)
> Merlin
>