On Mon, Nov 11, 2013 at 3:14 PM, Haribabu kommi <haribabu.ko...@huawei.com> wrote: > On 08 November 2013 18:35 Amit Kapila wrote: >> On Fri, Nov 8, 2013 at 10:56 AM, Haribabu kommi >> <haribabu.ko...@huawei.com> wrote: >> > On 07 November 2013 09:42 Amit Kapila wrote: >> >> I am not sure whether the same calculation as done for >> new_rel_tuples >> >> works for new_dead_tuples, you can once check it. >> > >> > I didn't find any way to calculate new_dead_tuples like >> new_rel_tuples. >> > I will check it. >> > >> > The two approaches calculations are approximation values only. >> > >> > 1. Taking a copy of n_dead_tuples before VACUUM starts and then >> subtract it once it is done. >> > This approach doesn't include the tuples which are remains during >> the vacuum operation. >> >> Wouldn't next or future vacuum's will make the estimate more >> appropraite? > > Possible only when nkeep counter value (tuples not cleaned) is very less > value.
Do you really expect too many dead tuples during Vacuum? >> > 2. nkeep counter contains the tuples which are still visible to other >> transactions. >> > This approach doesn't include tuples which are deleted on pages >> where vacuum operation is already finished. >> > >> > In my opinion the second approach gives the value nearer to the >> actual >> > value, because it includes some of the new dead tuples also. Please >> correct me if anything wrong in my analysis. >> I think main problem in nkeep logic is to come up with an estimation >> algorithm similar to live tuples. >> >> By the way, do you have test case or can you try to write a test case >> which can show this problem and then after fix, you can verify if the >> problem is resolved. > > The simulated index bloat problem can be generated using the attached script > and sql. > With the fix of setting the dead tuples properly, Which fix here you are referring to, is it the one which you have proposed with your initial mail? > the bloat is reduced and by changing the vacuum cost > Parameters the bloat is avoided. With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
