Should'd grid elements be ordered to allow pagination? On Oct 8, 2013, at 6:45 PM, Michele Comitini wrote:
> Whenever there is a big performance impact it's better not to make > assumptions on what is the most common use case. > I hate to hear the "web2py is slow" refrain because it's false if you have a > good knowledge of web2py. What concerns me is that doing hidden things that > impact on performance scares the newcomer and the casual tester. > > ------- > Suppose I am new to web2py, but not a newbie to programming and python. I > have a big database and I want to publish things out of it with a nice > framework. I know that accessing the db is critical. I heard web2py is easy > to use. > > I do a simple test. I want to know if there are more than one record of the > kind I am looking for: > > len(db(db.long_table.value=='Am I the only one > here?').select(db.long_table.id, limitby(0,2))) > > I expect it faster than count() on a really big table. Result slow as hell. > Consequence is ... ok I will use a better framework and I will post somewhere > that web2py is nice, but slow, not for serious projects. > ------- > > Even worse in older releases doing a db.long_table(value='Am I the only one > here?') was slow, very slow and those shortcuts in web2py code are used > everywhere. To the casual user it was the clear sign that no one did serious > testing on a large database. > > mic > > > > 2013/10/8 Niphlod <niph...@gmail.com> > the smartest thing to do would be to avoid orderby when there are less > records than paginate. > However, it's unusual to have a query misbehaving for a couple hundreds > records, and I really don't see the point on using grid with paginate=10000. > Given that pagination is 99% of the time required, we need to orderby on > something.... > What we should orderby to then? The only assured field that has an implicit > index is the id (being a PK). Orderby(ing) a PK should definitely not require > a full scan. > I don't see any particular case other than exceptional misbehaving tables to > turn off the ordering. > > > On Tuesday, October 8, 2013 1:53:50 PM UTC+2, Anthony wrote: > > db.table(id=3) is for returning the sole matching record, so you don't have > to worry about the database's arbitrary ordering of results. But when using > limitby to return a particular subset of records (e.g., when doing > pagination), don't you need to specify an orderby to guarantee that the > results on each query will remain in the same order? > > Yes you need to do it, and you need to do it in a proper way. That is why i > think that forcing orderby when limitby is used is not a good idea. Seems > just a hack for the grid, not a generic approach. IMHO it's better to be > explicit. > Consider that on datasets of size comparable to the window imposed by the > limitby, the result is that if one uses limitby then he goes slower than > without it, because of the implicit orderby. Maybe he wonders why (and all > sorts of bad things about web2py ;- ) > > I suppose we could default orderby_on_limitby to False in the general case > and leave it to the developer to explicitly orderby when using limitby, but > what do you propose for the grid? > > Anthony > > -- > Resources: > - http://web2py.com > - http://web2py.com/book (Documentation) > - http://github.com/web2py/web2py (Source code) > - https://code.google.com/p/web2py/issues/list (Report Issues) > --- > You received this message because you are subscribed to the Google Groups > "web2py-users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to web2py+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > -- Resources: - http://web2py.com - http://web2py.com/book (Documentation) - http://github.com/web2py/web2py (Source code) - https://code.google.com/p/web2py/issues/list (Report Issues) --- You received this message because you are subscribed to the Google Groups "web2py-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to web2py+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
