From simon@kx.com  Thu Mar  7 07:51:18 2013
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From: Simon Garland <simon@kx.com>
Date: Thu, 7 Mar 2013 13:50:40 +0100
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Subject: Re: Fwd: FW: GuestNet Access, monday 11th
To: Dennis Shasha <shasha@courant.nyu.edu>
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On 6 March 2013 17:26, Dennis Shasha <shasha@courant.nyu.edu> wrote:

> Dear Simon,
> Great. By the way, I think there is real interest (I got this
> question from my last bank of america course) in understanding
> when it's best to use RDB vs. HDB.
> I couldn't really answer the question.
>
> Also, I assume I'm talking sometime between 3:45 and 5.
> Best,
> Dennis
>

yes, you're on first with the slot 3:40 to 4:00
(I think you'll have received a reminder email yesterday automatically)

HDB and RDB
that's a big topic in a way, the quick answer is that the RDB is for the
intra-day data that's still pouring in from the feedhandlers, and HDB is
older data that's been neatly sorted and arranged for fast access, then
saved.

but with more sophisticated users there's more. In a way it's HDB and TP
(TickerPlant) where the RDB is just one of the clients for the TP. HDB is
fixed, but the TP allows you to query the whole day's data if you want via
the RDB - but it can allow far more, streaming queries to use the current
buzz-description. See c.q

http://kx.com/q/tick/c.q

(there's a version clog.q on code.kx that will start from the logged data)

that allows things like an instantaneous last trade+prevailing quote, last
10 trades and quotes, rolling HLOC, rolling VWAP

users just coming to it tend to think they should just munge RDB+HDB
together in a gateway, but that's missing out on a lot of what can be done
with the streaming nature of TP data

