Added to TODO: * Allow configuration of backend priorities via the operating system Though backend priorities make priority inversion during lock waits possible, research shows that this is not a huge problem. http://archives.postgresql.org/pgsql-general/2007-02/msg00493.php --------------------------------------------------------------------------- Ron Mayer wrote: > Bruce Momjian wrote: > > Hard to argue with that. > > Is it a strong enough argument to add a TODO? > > > I'm thinking some sort of TODO might be called for. > > Perhaps two TODOs? > * Use the OS's priority features to prioritize > backends (and document that it might work > better with OS's that support priority inheritance). > * Investigate if postgresql could develop an > additional priority mechanism instead of using > the OS's. > > > Ron Mayer wrote: > >> Magnus Hagander wrote: ... > >>> quite likely to suffer from priority inversion > >> ... CMU paper... tested PostgreSQL (and DB2) on TPC-C > >> and TPC-W ...found that...I/O scheduling through > >> CPU priorities is a big win for postgresql. > >> > >> http://www.cs.cmu.edu/~bianca/icde04.pdf > > Setting priorities seems a rather common request, > supposedly coming up every couple months [5]. > > The paper referenced [1] suggests that even with > naive schedulers, use of CPU priorities is very > effective for CPU and I/O intensive PostgreSQL > workloads. > > If someone eventually finds a workload that does suffer > worse performance due to priority inversion, > (a) they could switch to an OS and scheduler > that supports priority inheritance; > (b) it'd be an interesting case for a paper > rebutting the CMU one; and > (c) they don't have to use priorities. > > If a user does find he wants priority inheritance it > seems Linux[1], BSD[2], some flavors of Windows[3], > and Solaris[4] all seem to be options; even though > I've only seen PostgreSQL specifically tested for > priority inversion problems with Linux (which did > not find problems but found additional benefit of > using priority inheritance). > > > > > [1] Linux with Priority inheritance showing benefits for > PostgreSQL > http://www.cs.cmu.edu/~bianca/icde04.pdf > [2] BSD priority inheritance work mentioned: > http://www.freebsd.org/news/status/report-july-2004-dec-2004.html > [3] Windows priority inheritance stuff: > http://msdn2.microsoft.com/en-us/library/aa915356.aspx > [4] Solaris priority inheritance stuff > http://safari5.bvdep.com/0131482092/ch17lev1sec7 > http://www.itworld.com/AppDev/1170/swol-1218-insidesolaris/ > [5] Tom suggests that priorities are a often requested feature. > http://svr5.postgresql.org/pgsql-performance/2006-05/msg00463.php > > ---------------------------(end of broadcast)--------------------------- > TIP 3: Have you checked our extensive FAQ? > > http://www.postgresql.org/docs/faq -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. +
