Thanks for cleaning this up. On Wed, May 7, 2014 at 1:18 PM, Heikki Linnakangas <heikki.linnakan...@iki.fi> wrote: > The jsonb_exists_any and jsonb_exists_all functions no longer sort the input > array. That was a premature optimization, the idea being that if there are > duplicates in the input array, you only need to check them once. Also, > sorting the array saves some effort in the binary search used to find a key > within an object. But there were drawbacks too: the sorting and > deduplicating obviously isn't free, and in the typical case there are no > duplicates to remove, and the gain in the binary search was minimal. Remove > all that, which makes the code simpler too.
This is not the reason why the code did that. De-duplication was not the point at all. findJsonbValueFromSuperHeader()'s lowbound argument previously served to establish a low bound for searching when searching for multiple keys (so the second and subsequent user-supplied key could skip much of the object). In the case of jsonb_exists_any(), say, if you only have a reasonable expectation that about 1 key exists, and that happens to be the last key that the user passed to the text[] argument (to the existence/? operator), then n - 1 calls to what is now findJsonbValueFromContainer() (which now does not accept a lowbound) are wasted. That's elem_count - 1 top-level binary searches of the entire jsonb. Or elem_count such calls rather than 1 call (plus 1 sort of the supplied array) in the common case where jsonb_exists_any() will return false. Granted, that might not be that bad right now, given that it's only ever (say) elem_count or elem_count - 1 wasted binary searches through the *top* level, but that might not always be true. And even today, sorting a presumably much smaller user-passed lookup array once has to be cheaper than searching through the entire jsonb perhaps elem_count times per call. -- Peter Geoghegan -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers
