I second memory mapped files and mapped file database.
On Tue, Apr 8, 2014 at 4:51 PM, Raul Miller <[email protected]> wrote: > It's available for free now, with some limitations: > > http://kx.com/software-download.php > > It'll take me a few years, though, to develop a fluency in K (Q actually, > or kdb+ ...) which approaches my fluency in other languages. Anyways, it's > not at all clear that K (or Q or KDB+) would be any better for this > application than J. The grass is always greener on the other side of the > fence, especially after you've crossed it? > > Also, if I do my job properly, the language itself becomes irrelevant and > the data structures are straightforward enough to allow any arbitrary > language to be used. > > (Meanwhile, I've got J running on OpenBSD, which pleases me.) > > -- > Raul > > Thanks, > > -- > Raul > > > On Tue, Apr 8, 2014 at 2:54 PM, km <[email protected]> wrote: > > > I think I would pay for k's database capability. --Kip Murray > > > > Sent from my iPad > > > > > On Apr 8, 2014, at 12:46 PM, Björn Helgason <[email protected]> wrote: > > > > > > I would take a look at the mapped file database lab to get ideas. > > > > > > - > > > Björn Helgason > > > gsm:6985532 > > > skype:gosiminn > > >> On 8.4.2014 15:34, "Raul Miller" <[email protected]> wrote: > > >> > > >> I have thought about using symbols, but the only way to delete symbols > > that > > >> I know of involves exiting J. And, my starting premise was that I > would > > >> have too much data to fit into memory. > > >> > > >> For some computations it does make sense to start up an independent J > > >> session for each part of the calculation (and, in fact, that is what I > > am > > >> doing in a different aspect of dealing with this dataset - it's about > 10 > > >> terabytes, or so I am told - I've not actually seen it all yet and it > > takes > > >> time to upload it). But for some calculations you need to be able to > > >> correlate between pieces which have been dealt with elsewhere. > > >> > > >> A have similar reservations about fixed-width fields. There's just too > > much > > >> data for me to predict how wide the fields are going to be. In some > > cases I > > >> might actually be going with fixed-width, but that might be too > > inefficient > > >> for the general case. I've one field which would have to be over 100k > in > > >> width if it was fixed width, even though typical cases are shorter > than > > 1k. > > >> At some point I might go with fixed width, and I expect that doing so > > will > > >> cause me to lose a few records which will be discovered later in > > >> processing. That might not be a big deal, for this large of a data > set, > > but > > >> if it's not necessary why bother? > > >> > > >> Finally, Bjorn's suggestion of using mapped files does seem like a > good > > >> idea, at least for the character data. But that is an optimization and > > >> optimizations speed up some operations at the expense of slowing down > > other > > >> optimizations. So what really matters is the workload. > > >> > > >> Ultimately, for a dataset this large, it's going to take time. > > >> > > >> Thanks, > > >> > > >> -- > > >> Raul > > >> > > >> > > >> > > >> > > >>> On Tue, Apr 8, 2014 at 6:06 AM, Joe Bogner <[email protected]> > > wrote: > > >>> > > >>> It seems this representation is somewhat similar to how the symbol > > table > > >>> stores strings: > > >>> > > >>> http://m.jsoftware.com/help/dictionary/dsco.htm > > >>> > > >>> Also, did you consider using symbols? I've used symbols for string > > >> columns > > >>> that contain highly repetitive data, for example, an invoice table > with > > >> an > > >>> alpha-numeric SKU. > > >>> > > >>> Thanks for sharing > > >>> > > >>> > > >>> > > >>> > > >>> > > >>> > > >>> On Tue, Apr 8, 2014 at 2:40 AM, Raul Miller <[email protected]> > > >> wrote: > > >>> > > >>>> Consider this example: > > >>>> > > >>>> table=:<;._2;._2]0 :0 > > >>>> First Name,Last Name,Sum, > > >>>> Adam,Wallace,19, > > >>>> Travis,Smith,10, > > >>>> Donald,Barnell,8, > > >>>> Gary,Wallace,27, > > >>>> James,Smith,10, > > >>>> Sam,Johnson,10, > > >>>> Travis,Neal,11, > > >>>> Adam,Campbell,11, > > >>>> Walter,Abbott,13, > > >>>> ) > > >>>> > > >>>> Using boxed strings works great for relatively small sets of data. > But > > >>> when > > >>>> things get big, their overhead starts to hurt to much. (Big means: > so > > >>> much > > >>>> data that you'll probably not be able to fit it all in memory at the > > >> same > > >>>> time. So you need to plan on relatively frequent delays while > reading > > >>> from > > >>>> disk.) > > >>>> > > >>>> One alternative to boxed strings is segmented strings. A segmented > > >> string > > >>>> is an argument which could be passed to <;._1. It's basically just a > > >>> string > > >>>> with a prefix delimiter. You can work with these sorts of strings > > >>> directly, > > >>>> and achieve results similar to what you would achieve with boxed > > >> arrays. > > >>>> > > >>>> Segmented strings are a bit clumsier than boxed arrays - you lose a > > lot > > >>> of > > >>>> the integrity checks, so if you mess up you probably will not see an > > >>> error. > > >>>> So it's probably a good idea to model your code using boxed arrays > on > > a > > >>>> small set of data and then convert to segmented representation once > > >>> you're > > >>>> happy with how things work (and once you see a time cost that makes > it > > >>>> worth spending the time to rework your code). > > >>>> > > >>>> Also, to avoid having to use f;._2 (or whatever) every time, it's > good > > >> to > > >>>> do an initial pass on the data, to extract its structure. > > >>>> > > >>>> Here's an example: > > >>>> > > >>>> FirstName=:;LF&,each }.0{"1 table > > >>>> > > >>>> LastName=:;LF&,each }.1{"1 table > > >>>> > > >>>> Sum=:;LF&,each }.2{"1 table > > >>>> > > >>>> > > >>>> ssdir=: [:(}:,:2-~/\])I.@(= {.),# > > >>>> > > >>>> FirstNameDir=: ssdir FirstName > > >>>> LastNameDir=: ssdir LastName > > >>>> > > >>>> Actually, sum is numeric so let's just use a numeric representation > > for > > >>>> that column > > >>>> > > >>>> Sum=: _&".@> }.2{"1 table > > >>>> > > >>>> Which rows have a last name of Smith? > > >>>> > > >>>> <:({.LastNameDir) I. I.'Smith' E. LastName > > >>>> > > >>>> 1 4 > > >>>> > > >>>> > > >>>> Actually, there's an assumption there that Smith is not part of some > > >>> larger > > >>>> name. We can include the delimiter in the search if we are concerned > > >>> about > > >>>> that. For even more protection we could append a trailing delimiter > on > > >>> our > > >>>> segmented string and then search for (in this case) LF,'Smith',LF. > > >>>> > > >>>> > > >>>> Anyways, let's extract the corresponding sums and first name: > > >>>> > > >>>> > > >>>> 1 4{Sum > > >>>> > > >>>> 10 10 > > >>>> > > >>>> > > >>>> FirstName{~;<@(+ i.)/"1|:1 4 {"1 FirstNameDir > > >>>> > > >>>> > > >>>> Travis > > >>>> > > >>>> James > > >>>> > > >>>> > > >>>> Note that that last expression is a bit complicated. It's not so > bad, > > >>>> though, if what you are extracting is a small part of the total. > And, > > >> in > > >>>> that case, using a list of indices to express a boolean result seems > > >>> like a > > >>>> good thing. You wind up working with set operations (intersection > and > > >>>> union) rather than logical operations (and and or). Also, set > > >> difference > > >>>> instead of logical not (dyadic -. instead of monadic -.). > > >>>> > > >>>> > > >>>> intersect=: [ -. -. > > >>>> > > >>>> union=. ~.@, > > >>>> > > >>>> > > >>>> (It looks like I might be using this kind of thing really soon, so I > > >>>> thought I'd lay down my thoughts here and invite comment.) > > >>>> > > >>>> > > >>>> Thanks, > > >>>> > > >>>> > > >>>> -- > > >>>> > > >>>> Raul > > >>>> > ---------------------------------------------------------------------- > > >>>> For information about J forums see > > http://www.jsoftware.com/forums.htm > > >>>> > > >>> > ---------------------------------------------------------------------- > > >>> For information about J forums see > http://www.jsoftware.com/forums.htm > > >>> > > >> ---------------------------------------------------------------------- > > >> For information about J forums see > http://www.jsoftware.com/forums.htm > > >> > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
