2018-07-30 13:19 GMT+02:00 Jeff Janes <jeff.ja...@gmail.com>: > On Mon, Jul 30, 2018 at 12:11 AM, Pavel Stehule <pavel.steh...@gmail.com> > wrote: > >> 2018-07-30 1:00 GMT+02:00 Tom Lane <t...@sss.pgh.pa.us>: >> >>> David Rowley <david.row...@2ndquadrant.com> writes: >>> > On 29 July 2018 at 17:38, Dinesh Kumar <dns98...@gmail.com> wrote: >>> >> I found performance variance between accessing int1 and int200 column >>> which >>> >> is quite large. >>> >>> > Have a look at slot_deform_tuple and heap_deform_tuple. You'll see >>> > that tuples are deformed starting at the first attribute. If you ask >>> > for attribute 200 then it must deform 1-199 first. >>> >>> Note that that can be optimized away in some cases, though evidently >>> not the one the OP is testing. From memory, you need a tuple that >>> contains no nulls, and all the columns to the left of the target >>> column have to be fixed-width datatypes. Otherwise, the offset to >>> the target column is uncertain, and we have to search for it. >>> >> >> JIT decrease a overhead of this. >> > > The bottleneck here is such a simple construct, I don't see how JIT could > improve it by much. > > And indeed, in my hands JIT makes it almost 3 times worse. > > Run against ab87b8fedce3fa77ca0d6, I get 12669.619 ms for the 2nd JIT > execution and 4594.994 ms for the JIT=off. >
look on http://www.postgresql-archive.org/PATCH-LLVM-tuple-deforming-improvements-td6029385.html thread, please. Regards Pavel > Cheers, > > Jeff >
