FYI, I have added a number of these emails to the 'thread' TODO.detail list.
> On Wed, 26 Sep 2001, D. Hageman wrote: > > > > > Save for the fact that the kernel can switch between threads faster then > > > > it can switch processes considering threads share the same address space, > > > > stack, code, etc. If need be sharing the data between threads is much > > > > easier then sharing between processes. > > > > > > When using a kernel threading model, it's not obvious to me that the > > > kernel will switch between threads much faster than it will switch > > > between processes. As far as I can see, the only potential savings is > > > not reloading the pointers to the page tables. That is not nothing, > > > but it is also > <major snippage> > > > > I can't comment on the "isolate data" line. I am still trying to figure > > > > that one out. > > > > > > Sometimes you need data which is specific to a particular thread. > > > > When you need data that is specific to a thread you use a TSD (Thread > > Specific Data). > Which Linux does not support with a vengeance, to my knowledge. > > As a matter of fact, quote from Linus on the matter was something like > "Solution to slow process switching is fast process switching, not another > kernel abstraction [referring to threads and TSD]". TSDs make > implementation of thread switching complex, and fork() complex. > > The question about threads boils down to: Is there far more data that is > shared than unshared? If yes, threads are better, if not, you'll be > abusing TSD and slowing things down. > > I believe right now, postgresql' model of sharing only things that need to > be shared is pretty damn good. The only slight problem is overhead of > forking another backend, but its still _fast_. > > IMHO, threads would not bring large improvement to postgresql. > > Actually, if I remember, there was someone who ported postgresql (I think > it was 6.5) to be multithreaded with major pain, because the requirement > was to integrate with CORBA. I believe that person posted some benchmarks > which were essentially identical to non-threaded postgres... > > -alex > > > ---------------------------(end of broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://archives.postgresql.org > -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026 ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
