On Tue, Sep 15, 2015 at 3:03 PM, Teodor Sigaev <teo...@sigaev.ru> wrote: > > > Paul Jungwirth wrote: >>> >>> Or something like this in pseudocode: >>> >>> numeric = int8_numeric(*(uint64 *)(&i->data[0])) * >>> int8_numeric(MAX_INT64) + int8_numeric(*(uint64 *)(&i->data[8])) >> >> >> This is more like what I was hoping for, rather than converting to a >> string and back. Would you mind confirming for me: int8_numeric turns an >> int64 into an arbitrary-precision numeric Datum? So there is no overflow >> risk here? > > Sure, no risk. Numeric precision is limited 1000 digits with magnitude 1000 > > >> >> But it looks like int8_numeric takes a *signed* integer. Isn't that a >> problem? I suppose I could get it working though by jumping through some >> hoops. > > signed vs unsigned problem does not exist actually, because of precision of > numeric is much better than we need and presence of numeric_abs. > > >> Yes, but that seems like an unrealistic concern. Even "only" 2^64 is >> 18446744073709551616 records. Or another way of thinking about it, if 64 > > :) "only" > >> bits (or 32) is a good enough penalty input for all the other data >> types, why not for UUIDs? Keep in mind type 3-5 UUIDs should be evenly >> distributed. Perhaps we could use the bottom half (instead of the top) >> to ensure even distribution for type 1 and 2 too. > > it must be. But UUID could be taken for unknown source and we can't predict > distribution. I believe pg generates them correctly, but other generators > could be not so good. > >> It seems to me that using only the top half should be okay, but if you >> believe it's not I'll go with the int8_numeric approach (in three chunks >> instead of two to work around signed-vs-unsigned). > > Yes, I believe. It is not good case when we can ruin index performance with > special set of value. > > Some difficulty which I see is how to transform numeric penalty to double > as it requires by GiST. May be, penalty/(INT_MAX64*INT_MAX64 + INT_MAX64)? > Keep in mind, that penalty is how range will be enlarged after range union, > so minimal penalty is 0 and maximum is 0xffffffffffffffffffffffffffffffff
This patch has been marked as "returned with feedback" for CF 2015-11 because of the presence of a review and a certain lack of activity.. Please free to move it to next CF if you think that's more adapted. -- Michael -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
