>On Thursday, 14 November, 2019 03:52, Dominique Devienne <ddevie...@gmail.com> >wrote:
>>On Sat, Nov 9, 2019 at 1:20 PM Mario M. Westphal <m...@mwlabs.de> wrote: >>> Thanks to all the friendly people who commented on my question. Much >>> appreciated :-) >>> I was able to solve this with a small trick: >>> I created a small 'state' struct with a rowid and the result (float) >>> for that row. >> Sounds like you re-invented >> https://www.sqlite.org/c3ref/get_auxdata.html >> but with global state, no? >> I replied to your original thread with that link, before seeing this >> message. Using the built-in SQLite >> mechanism for function caching is much better, because it's clean, and >> properly handles the lifetime >> of the cache, tying it to the statement execution lifetime. >get/set auxdata is apparently intended to cache auxillary data associated >with a CONSTANT provided to a function parameter, not the dynamic result >of a computation. I suppose you could attempt to store your cache >results against argument 2 (the table column), however that will probably >not achieve the effect desired since this is not the purpose of get/set >auxdata (read the web page describing it). And storing it against >argument 1 will not work because, although that is a constant, how would >you ever know when the *value* of argument 2 changed? >Maybe I will write a wee test to see if it does work as you think or if >it only works as documented. The function only works as documented in that auxdata set against non-constant parameters is not maintained. This could be made to work with "some random function" where one of the parameters is a constant or a bound parameter by passing the cache determinant as a parameter and caching the determinant and the result against the constant agrument. eg: expensive_function(?99, vdata, rowid) could have a structure containing a arg[2] and the result, and set this as auxdata against argument 0 anytime it is computed. Before computing one would check that the retrieved auxdata rowid == arg[2] and if so simply return the result from the auxdata. This assumes that the value of vdata is dependant on the value of rowid, of course. You can of course move the parameters around, but only auxdata stored against a constant has a chance of being preserved. In this case the constant is a bound value. Where there is no constant, you would have to "create" one ... eg expensive_function(1, rowid, data1) so that you have somewhere to store the auxdata ... -- The fact that there's a Highway to Hell but only a Stairway to Heaven says a lot about anticipated traffic volume. _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
