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memory loads or pressures, but will the optimizer vary the degree of paralellism based on the number of already active threads or the system cpu load? -- Kevin Connell, MCDBA -------------------------------------------------- The views expressed here are my own and not of my employer. ----------------------------------------------------
Not at run time... At most the optimizer will output 2 plans, one serial and
one parallell... If for any reason there are not enough resources at run time to do the parallel plan, the serial plan is run... SQL does not currently back off of the number of processors, etc... -- Wayne Snyder, MCDBA, SQL Server MVP Computer Education Services Corporation (CESC), Charlotte, NC www.computeredservices.com (Please respond only to the newsgroups.) I support the Professional Association of SQL Server (PASS) and it's community of SQL Server professionals. www.sqlpass.org [quoted text, click to view] "Kevin" <ReplyTo@Newsgroups.only> wrote in message news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > So, we know that the optimizer may choose certain join types under different > memory loads or pressures, but will the optimizer vary the degree of > paralellism based on the number of already active threads or the system cpu > load? > > -- > Kevin Connell, MCDBA > -------------------------------------------------- > The views expressed here are my own > and not of my employer. > ---------------------------------------------------- > >
No, is based only upon cost of the query, not current activity not current
load. [quoted text, click to view] "Kevin" <ReplyTo@Newsgroups.only> wrote in message news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > So, we know that the optimizer may choose certain join types under different > memory loads or pressures, but will the optimizer vary the degree of > paralellism based on the number of already active threads or the system cpu > load? > > -- > Kevin Connell, MCDBA > -------------------------------------------------- > The views expressed here are my own > and not of my employer. > ---------------------------------------------------- > >
[quoted text, click to view] > No, is based only upon cost of the query, not current activity not current > load. From the SQL Server 2000 Books Online: <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> SQL Server monitors CPU usage and adjusts the degree of parallelism at the query startup time. Lower degrees of parallelism are chosen if CPU usage is high. </Excerpt> -- Hope this helps. Dan Guzman SQL Server MVP ----------------------- SQL FAQ links (courtesy Neil Pike): http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 http://www.sqlserverfaq.com http://www.mssqlserver.com/faq ----------------------- [quoted text, click to view] "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > No, is based only upon cost of the query, not current activity not current > load. > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > So, we know that the optimizer may choose certain join types under > different > > memory loads or pressures, but will the optimizer vary the degree of > > paralellism based on the number of already active threads or the system > cpu > > load? > > > > -- > > Kevin Connell, MCDBA > > -------------------------------------------------- > > The views expressed here are my own > > and not of my employer. > > ---------------------------------------------------- > > > > > >
That's what I was looking for. Maybe I'll send a request for a "knob" on
this one to sqlwish :) -- Kevin Connell, MCDBA -------------------------------------------------- The views expressed here are my own and not of my employer. ---------------------------------------------------- [quoted text, click to view] "Dan Guzman" <danguzman@nospam-earthlink.net> wrote in message news:eLpn4XvhDHA.944@TK2MSFTNGP11.phx.gbl... > > > No, is based only upon cost of the query, not current activity not > current > > load. > > From the SQL Server 2000 Books Online: > > <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> > > SQL Server monitors CPU usage and adjusts the degree of parallelism at > the query startup time. Lower degrees of parallelism are chosen if CPU > usage is high. > > </Excerpt> > > -- > Hope this helps. > > Dan Guzman > SQL Server MVP > > ----------------------- > SQL FAQ links (courtesy Neil Pike): > > http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 > http://www.sqlserverfaq.com > http://www.mssqlserver.com/faq > ----------------------- > > "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message > news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > > No, is based only upon cost of the query, not current activity not > current > > load. > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > > So, we know that the optimizer may choose certain join types under > > different > > > memory loads or pressures, but will the optimizer vary the degree of > > > paralellism based on the number of already active threads or the > system > > cpu > > > load? > > > > > > -- > > > Kevin Connell, MCDBA > > > -------------------------------------------------- > > > The views expressed here are my own > > > and not of my employer. > > > ---------------------------------------------------- > > > > > > > > > > > >
I'm planning on doing some testing. Should be pretty straightforward to
figure out. [quoted text, click to view] "Gert-Jan Strik" <sorry@toomuchspamalready.nl> wrote in message news:3F79D788.139C5712@toomuchspamalready.nl... > Dan, > > That is interesting. Do you know if any number of CPU's is being > considered? Or will SQL-Server scale back to a fixed number of CPU's > (for example 2, 4, 8) or will it simply scale back to 1 (and use the > serial query plan)? > > I assume the degree of parallism is determined before the query plan for > this number of CPU's is compiled (or fetched from cache). > > Gert-Jan > > > Dan Guzman wrote: > > > > > No, is based only upon cost of the query, not current activity not > > current > > > load. > > > > From the SQL Server 2000 Books Online: > > > > <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> > > > > SQL Server monitors CPU usage and adjusts the degree of parallelism at > > the query startup time. Lower degrees of parallelism are chosen if CPU > > usage is high. > > > > </Excerpt> > > > > -- > > Hope this helps. > > > > Dan Guzman > > SQL Server MVP > > > > ----------------------- > > SQL FAQ links (courtesy Neil Pike): > > > > http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 > > http://www.sqlserverfaq.com > > http://www.mssqlserver.com/faq > > ----------------------- > > > > "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message > > news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > > > No, is based only upon cost of the query, not current activity not > > current > > > load. > > > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > > > So, we know that the optimizer may choose certain join types under > > > different > > > > memory loads or pressures, but will the optimizer vary the degree of > > > > paralellism based on the number of already active threads or the > > system > > > cpu > > > > load? > > > > > > > > -- > > > > Kevin Connell, MCDBA > > > > -------------------------------------------------- > > > > The views expressed here are my own > > > > and not of my employer. > > > > ---------------------------------------------------- > > > > > > > > > > > > > >
Dan,
That is interesting. Do you know if any number of CPU's is being considered? Or will SQL-Server scale back to a fixed number of CPU's (for example 2, 4, 8) or will it simply scale back to 1 (and use the serial query plan)? I assume the degree of parallism is determined before the query plan for this number of CPU's is compiled (or fetched from cache). Gert-Jan [quoted text, click to view] Dan Guzman wrote:
> > > No, is based only upon cost of the query, not current activity not > current > > load. > > From the SQL Server 2000 Books Online: > > <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> > > SQL Server monitors CPU usage and adjusts the degree of parallelism at > the query startup time. Lower degrees of parallelism are chosen if CPU > usage is high. > > </Excerpt> > > -- > Hope this helps. > > Dan Guzman > SQL Server MVP > > ----------------------- > SQL FAQ links (courtesy Neil Pike): > > http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 > http://www.sqlserverfaq.com > http://www.mssqlserver.com/faq > ----------------------- > > "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message > news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > > No, is based only upon cost of the query, not current activity not > current > > load. > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > > So, we know that the optimizer may choose certain join types under > > different > > > memory loads or pressures, but will the optimizer vary the degree of > > > paralellism based on the number of already active threads or the > system > > cpu > > > load? > > > > > > -- > > > Kevin Connell, MCDBA > > > -------------------------------------------------- > > > The views expressed here are my own > > > and not of my employer. > > > ---------------------------------------------------- > > > > > > > >
[quoted text, click to view]
> That is interesting. Do you know if any number of CPU's is being > considered? Or will SQL-Server scale back to a fixed number of CPU's > (for example 2, 4, 8) or will it simply scale back to 1 (and use the > serial query plan)? > > I assume the degree of parallism is determined before the query plan for > this number of CPU's is compiled (or fetched from cache). My interpretation of the following (from the same topic) is that the number of CPUs is variable and the optimal number of threads is reevaluated for each execution: <Excerpt> SQL Server reexamines the optimal number of thread decisions each time a query execution plan is retrieved from the procedure cache. For example, one execution of a query can result in use of a serial plan, a later execution of the same query can result in a parallel plan using three threads, and a third execution can result in a parallel plan using four threads. </Excerpt> I haven't played around with this, though. Hopefully, Kevin will post the results of his tests. -- Hope this helps. Dan Guzman SQL Server MVP [quoted text, click to view] "Gert-Jan Strik" <sorry@toomuchspamalready.nl> wrote in message news:3F79D788.139C5712@toomuchspamalready.nl... > Dan, > > That is interesting. Do you know if any number of CPU's is being > considered? Or will SQL-Server scale back to a fixed number of CPU's > (for example 2, 4, 8) or will it simply scale back to 1 (and use the > serial query plan)? > > I assume the degree of parallism is determined before the query plan for > this number of CPU's is compiled (or fetched from cache). > > Gert-Jan > > > Dan Guzman wrote: > > > > > No, is based only upon cost of the query, not current activity not > > current > > > load. > > > > From the SQL Server 2000 Books Online: > > > > <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> > > > > SQL Server monitors CPU usage and adjusts the degree of parallelism at > > the query startup time. Lower degrees of parallelism are chosen if CPU > > usage is high. > > > > </Excerpt> > > > > -- > > Hope this helps. > > > > Dan Guzman > > SQL Server MVP > > > > ----------------------- > > SQL FAQ links (courtesy Neil Pike): > > > > http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 > > http://www.sqlserverfaq.com > > http://www.mssqlserver.com/faq > > ----------------------- > > > > "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message > > news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > > > No, is based only upon cost of the query, not current activity not > > current > > > load. > > > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > > > So, we know that the optimizer may choose certain join types under > > > different > > > > memory loads or pressures, but will the optimizer vary the degree of > > > > paralellism based on the number of already active threads or the > > system > > > cpu > > > > load? > > > > > > > > -- > > > > Kevin Connell, MCDBA > > > > -------------------------------------------------- > > > > The views expressed here are my own > > > > and not of my employer. > > > > ---------------------------------------------------- > > > > > > > > > > > > > >
[quoted text, click to view]
> I'm planning on doing some testing. Should be pretty straightforward to > figure out. Please share your results with the group. -- Hope this helps. Dan Guzman SQL Server MVP [quoted text, click to view] "Kevin" <ReplyTo@Newsgroups.only> wrote in message news:u7Ux3%238hDHA.944@TK2MSFTNGP11.phx.gbl... > I'm planning on doing some testing. Should be pretty straightforward to > figure out. > > > "Gert-Jan Strik" <sorry@toomuchspamalready.nl> wrote in message > news:3F79D788.139C5712@toomuchspamalready.nl... > > Dan, > > > > That is interesting. Do you know if any number of CPU's is being > > considered? Or will SQL-Server scale back to a fixed number of CPU's > > (for example 2, 4, 8) or will it simply scale back to 1 (and use the > > serial query plan)? > > > > I assume the degree of parallism is determined before the query plan for > > this number of CPU's is compiled (or fetched from cache). > > > > Gert-Jan > > > > > > Dan Guzman wrote: > > > > > > > No, is based only upon cost of the query, not current activity not > > > current > > > > load. > > > > > > From the SQL Server 2000 Books Online: > > > > > > <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> > > > > > > SQL Server monitors CPU usage and adjusts the degree of parallelism at > > > the query startup time. Lower degrees of parallelism are chosen if CPU > > > usage is high. > > > > > > </Excerpt> > > > > > > -- > > > Hope this helps. > > > > > > Dan Guzman > > > SQL Server MVP > > > > > > ----------------------- > > > SQL FAQ links (courtesy Neil Pike): > > > > > > http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 > > > http://www.sqlserverfaq.com > > > http://www.mssqlserver.com/faq > > > ----------------------- > > > > > > "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message > > > news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > > > > No, is based only upon cost of the query, not current activity not > > > current > > > > load. > > > > > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > > > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > > > > So, we know that the optimizer may choose certain join types under > > > > different > > > > > memory loads or pressures, but will the optimizer vary the degree of > > > > > paralellism based on the number of already active threads or the > > > system > > > > cpu > > > > > load? > > > > > > > > > > -- > > > > > Kevin Connell, MCDBA > > > > > -------------------------------------------------- > > > > > The views expressed here are my own > > > > > and not of my employer. > > > > > ---------------------------------------------------- > > > > > > > > > > > > > > > > > > > >
Either my test is no good or the documentation is incorrect. DOP is not
affected by system CPU load. I've been running a machine at 100% CPU load for hours now and large paralell queries continue to come in at DOP=4 Environment: 4 CPU ML-570G2 (4x2.0Ghz XEON P4) Win2k Std Sp3 SQL 2K Enterprise Sp3+ms03-031 4GB RAM sp_config:maxdop = 0 Measuring DOP with profiler event class "Degree of Paralellism" and verifying execution plan is paralell via QA. Would love to know if someone else can verify these findings. Kevin Connell, MCDBA -------------------------------------------------- [quoted text, click to view] "Dan Guzman" <danguzman@nospam-earthlink.net> wrote in message news:%23zdG5CIiDHA.2192@TK2MSFTNGP09.phx.gbl... > > I'm planning on doing some testing. Should be pretty straightforward > to > > figure out. > > Please share your results with the group. > > -- > Hope this helps. > > Dan Guzman > SQL Server MVP > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > news:u7Ux3%238hDHA.944@TK2MSFTNGP11.phx.gbl... > > I'm planning on doing some testing. Should be pretty straightforward > to > > figure out. > > > > > > "Gert-Jan Strik" <sorry@toomuchspamalready.nl> wrote in message > > news:3F79D788.139C5712@toomuchspamalready.nl... > > > Dan, > > > > > > That is interesting. Do you know if any number of CPU's is being > > > considered? Or will SQL-Server scale back to a fixed number of CPU's > > > (for example 2, 4, 8) or will it simply scale back to 1 (and use the > > > serial query plan)? > > > > > > I assume the degree of parallism is determined before the query plan > for > > > this number of CPU's is compiled (or fetched from cache). > > > > > > Gert-Jan > > > > > > > > > Dan Guzman wrote: > > > > > > > > > No, is based only upon cost of the query, not current activity > not > > > > current > > > > > load. > > > > > > > > From the SQL Server 2000 Books Online: > > > > > > > > <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> > > > > > > > > SQL Server monitors CPU usage and adjusts the degree of > parallelism at > > > > the query startup time. Lower degrees of parallelism are chosen if > CPU > > > > usage is high. > > > > > > > > </Excerpt> > > > > > > > > -- > > > > Hope this helps. > > > > > > > > Dan Guzman > > > > SQL Server MVP > > > > > > > > ----------------------- > > > > SQL FAQ links (courtesy Neil Pike): > > > > > > > > http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 > > > > http://www.sqlserverfaq.com > > > > http://www.mssqlserver.com/faq > > > > ----------------------- > > > > > > > > "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message > > > > news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > > > > > No, is based only upon cost of the query, not current activity > not > > > > current > > > > > load. > > > > > > > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > > > > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > > > > > So, we know that the optimizer may choose certain join types > under > > > > > different > > > > > > memory loads or pressures, but will the optimizer vary the > degree of > > > > > > paralellism based on the number of already active threads or > the > > > > system > > > > > cpu > > > > > > load? > > > > > > > > > > > > -- > > > > > > Kevin Connell, MCDBA > > > > > > -------------------------------------------------- > > > > > > The views expressed here are my own > > > > > > and not of my employer. > > > > > > ---------------------------------------------------- > > > > > > > > > > > > > > > > > > > > > > > > > > > >
I'll see what I can find out.
-- Hope this helps. Dan Guzman SQL Server MVP [quoted text, click to view] "Kevin" <ReplyTo@Newsgroups.only> wrote in message news:O7Z4WPViDHA.2592@tk2msftngp13.phx.gbl... > Either my test is no good or the documentation is incorrect. DOP is not > affected by system CPU load. > > I've been running a machine at 100% CPU load for hours now and large > paralell queries continue to come in at DOP=4 > > Environment: > 4 CPU ML-570G2 (4x2.0Ghz XEON P4) > Win2k Std Sp3 > SQL 2K Enterprise Sp3+ms03-031 > 4GB RAM > sp_config:maxdop = 0 > Measuring DOP with profiler event class "Degree of Paralellism" and > verifying execution plan is paralell via QA. > > Would love to know if someone else can verify these findings. > > Kevin Connell, MCDBA > -------------------------------------------------- > > > "Dan Guzman" <danguzman@nospam-earthlink.net> wrote in message > news:%23zdG5CIiDHA.2192@TK2MSFTNGP09.phx.gbl... > > > I'm planning on doing some testing. Should be pretty straightforward > > to > > > figure out. > > > > Please share your results with the group. > > > > -- > > Hope this helps. > > > > Dan Guzman > > SQL Server MVP > > > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > news:u7Ux3%238hDHA.944@TK2MSFTNGP11.phx.gbl... > > > I'm planning on doing some testing. Should be pretty straightforward > > to > > > figure out. > > > > > > > > > "Gert-Jan Strik" <sorry@toomuchspamalready.nl> wrote in message > > > news:3F79D788.139C5712@toomuchspamalready.nl... > > > > Dan, > > > > > > > > That is interesting. Do you know if any number of CPU's is being > > > > considered? Or will SQL-Server scale back to a fixed number of CPU's > > > > (for example 2, 4, 8) or will it simply scale back to 1 (and use the > > > > serial query plan)? > > > > > > > > I assume the degree of parallism is determined before the query plan > > for > > > > this number of CPU's is compiled (or fetched from cache). > > > > > > > > Gert-Jan > > > > > > > > > > > > Dan Guzman wrote: > > > > > > > > > > > No, is based only upon cost of the query, not current activity > > not > > > > > current > > > > > > load. > > > > > > > > > > From the SQL Server 2000 Books Online: > > > > > > > > > > <Excerpt href="architec.chm::/8_ar_sa_163x.htm"> > > > > > > > > > > SQL Server monitors CPU usage and adjusts the degree of > > parallelism at > > > > > the query startup time. Lower degrees of parallelism are chosen if > > CPU > > > > > usage is high. > > > > > > > > > > </Excerpt> > > > > > > > > > > -- > > > > > Hope this helps. > > > > > > > > > > Dan Guzman > > > > > SQL Server MVP > > > > > > > > > > ----------------------- > > > > > SQL FAQ links (courtesy Neil Pike): > > > > > > > > > > http://www.ntfaq.com/Articles/Index.cfm?DepartmentID=800 > > > > > http://www.sqlserverfaq.com > > > > > http://www.mssqlserver.com/faq > > > > > ----------------------- > > > > > > > > > > "Anthony Zessin" <Anthony.Zessin@rrtc.com> wrote in message > > > > > news:urGQxfthDHA.2212@tk2msftngp13.phx.gbl... > > > > > > No, is based only upon cost of the query, not current activity > > not > > > > > current > > > > > > load. > > > > > > > > > > > > "Kevin" <ReplyTo@Newsgroups.only> wrote in message > > > > > > news:OaXAe4GhDHA.2080@TK2MSFTNGP12.phx.gbl... > > > > > > > So, we know that the optimizer may choose certain join types > > under > > > > > > different > > > > > > > memory loads or pressures, but will the optimizer vary the > > degree of > > > > > > > paralellism based on the number of already active threads or > > the > > > > > system > > > > > > cpu > > > > > > > load? > > > > > > > > > > > > > > -- > > > > > > > Kevin Connell, MCDBA > > > > > > > -------------------------------------------------- > > > > > > > The views expressed here are my own > > > > > > > and not of my employer. > > > > > > > ---------------------------------------------------- > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
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