Tom, should I apply this patch now? Are you still considering other options for this?
--------------------------------------------------------------------------- Bruce Momjian wrote: > > Tom, I ran your tests with fsync off (as you did), and saw numbers > bouncing between 400-700 tps without my patch, and sticking at 700 tps > with my patch. > > --------------------------------------------------------------------------- > > Bruce Momjian wrote: > > > > The attached patch requires the new row to fit, and 10% to be free on > > the page. Would someone test that? > > > > --------------------------------------------------------------------------- > > > > Tom Lane wrote: > > > ITAGAKI Takahiro <[EMAIL PROTECTED]> writes: > > > > This is a revised patch originated by Junji TERAMOTO for HEAD. > > > > [BTree vacuum before page splitting] > > > > http://archives.postgresql.org/pgsql-patches/2006-01/msg00301.php > > > > I think we can resurrect his idea because we will scan btree pages > > > > at-atime now; the missing-restarting-point problem went away. > > > > > > I've applied this but I'm now having some second thoughts about it, > > > because I'm seeing an actual *decrease* in pgbench numbers from the > > > immediately prior CVS HEAD code. Using > > > pgbench -i -s 10 bench > > > pgbench -c 10 -t 1000 bench (repeat this half a dozen times) > > > with fsync off but all other settings factory-stock, what I'm seeing > > > is that the first run looks really good but subsequent runs tail off in > > > spectacular fashion :-( Pre-patch there was only minor degradation in > > > successive runs. > > > > > > What I think is happening is that because pgbench depends so heavily on > > > updating existing records, we get into a state where an index page is > > > about full and there's one dead tuple on it, and then for each insertion > > > we have > > > > > > * check for uniqueness marks one more tuple dead (the > > > next-to-last version of the tuple) > > > * newly added code removes one tuple and does a write > > > * now there's enough room to insert one tuple > > > * lather, rinse, repeat, never splitting the page. > > > > > > The problem is that we've traded splitting a page every few hundred > > > inserts for doing a PageIndexMultiDelete, and emitting an extra WAL > > > record, on *every* insert. This is not good. > > > > > > Had you done any performance testing on this patch, and if so what > > > tests did you use? I'm a bit hesitant to try to fix it on the basis > > > of pgbench results alone. > > > > > > One possible fix that comes to mind is to only perform the cleanup > > > if we are able to remove more than one dead tuple (perhaps about 10 > > > would be good). Or do the deletion anyway, but then go ahead and > > > split the page unless X amount of space has been freed (where X is > > > more than just barely enough for the incoming tuple). > > > > > > After all the thought we've put into this, it seems a shame to > > > just abandon it :-(. But it definitely needs more tweaking. > > > > > > regards, tom lane > > > > > > ---------------------------(end of broadcast)--------------------------- > > > TIP 4: Have you searched our list archives? > > > > > > http://archives.postgresql.org > > > > -- > > Bruce Momjian [EMAIL PROTECTED] > > EnterpriseDB http://www.enterprisedb.com > > > > + If your life is a hard drive, Christ can be your backup. + > > > > > > ---------------------------(end of broadcast)--------------------------- > > TIP 2: Don't 'kill -9' the postmaster > > -- > Bruce Momjian [EMAIL PROTECTED] > EnterpriseDB http://www.enterprisedb.com > > + If your life is a hard drive, Christ can be your backup. + -- Bruce Momjian [EMAIL PROTECTED] EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
