happstack-ixset internals/performance (was Re: [Haskell-cafe] Inverse of HaskellDB)

Thomas M. DuBuisson thomas.dubuisson at gmail.com
Sat Oct 2 16:09:03 EDT 2010

Thanks Jeremy, I just wrote up my own little analysis (below) while you
were responding.  I'll look for the kd-tree work; if I see discussion
(and am stupid enough to heap more work onto my plate) then I might get

Oops, didn't send...



So another glance tells me there is a list of maps (one element for each
index method) and it uses Data.Map under the hood.  So I have O(m lg n)
where m is the number of index methods and n is the number of elements.

Space wise, I think Data.Map takes up 6 words per Bin constructor (1 for
the constructor, 1 for the 'Size' and one for the pointer indirection
for each additional field), so the space is "6 * n * m * w" where w is
the word size.  This means indexing by 5 methods for 1M entries takes
about 256MB, assuming 28B per entry that's 28MB of data + 256 indexing ~
282MB needed.

Indexing my imaginary 1B points by user,date,lat,lon is 6 * 2^30 * 4 * 8
- or about 192 GB of indexing + 28GB of data for 220GB total.  Obviously
I shouldn't be talking about keeping a live data set of 28GB in memory
let alone indexing it all, but I was just curious about the ratio (220MB
for 1M points, which is just one heavy user).

On Sat, 2010-10-02 at 14:09 -0500, Jeremy Shaw wrote:
> In the current version of IxSet, the performance of querying on just
> the Lon would be essentially the same as if you just had a "Data.Map
> Lon Point". But the queries on the second index are current not so
> great. There is work in progress to rewrite the internals of IxSet to
> be based on a kd-tree, in which case your query should be pretty
> efficient.
> So, that answer is pretty vague :) I am in the process of wrapping up
> happstack 0.6 which has focused on fixing some performance issues with
> happstack-server, and refactoring the code so that user API and
> internals are more clearly separated and better documented.
> happstack 0.7 is all about happstack-state. A key aspect will be
> nailing down some solid performance benchmarks instead of vague hand
> waving :)
> The numbers you give are certainly within the scope of what we would
> like 0.7 to be able to handle. Also, I should note that
> happstack-state and happstack-ixset are independent from each other.
> You can easily use something other than IxSet to store your points and
> still use happstack-state.
> - jeremy
> On Fri, Oct 1, 2010 at 1:53 PM, Thomas M. DuBuisson
> <thomas.dubuisson at gmail.com> wrote:
> >> That is pretty close to how it would look using happstack-state. Here
> >> is a complete, runnable example which defines the types, a query,
> >> creates/initializes the database, performs the query, and prints the
> >> results.
> > [snip]
> >
> > How is data stored in Happstack.State?  I see the "Component" instance
> > uses "fromList" from happstack-ixset but can't find any information on
> > the algorithm used or its efficiency (computationally or wrt space).
> >
> > If making this more concrete helps then here is a possible use:
> >
> > == GPS Points ==
> > I have a GPS logger that logs every 10 seconds when I jog.  Jogging for
> > an hour a day for the past 180 days has resulted in 64k points.
> > Pretending I hosted a site for joggers (and all points were in the same
> > DB) I could easily result in a billion points (< 20K users).  Would
> > happstack-ixset code in the form "points @< (Lon -120) @> (Lon -125) @>
> > (Lat 45) @< (Lat 50)" perform reasonably?
> >
> > Cheers,
> > Thomas
> >
> >

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