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List:       rrd-users
Subject:    Re: [rrd-users] Forcing our own dates?
From:       Steve Shipway <s.shipway () auckland ! ac ! nz>
Date:       2011-02-08 22:25:08
Message-ID: 28E447343A85354483BCF7C3E9D5EAA514A806D3 () uxcn10-1 ! UoA ! auckland ! ac ! nz
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> is it possible to retrieve the date from the db as part of an overall
> query as opposed to using the current system date for the plotting of a
> graph. For example say I have a join that will show me the following:

I think you might be misunderstanding the nature of the RRD.  It is not a relational \
database, and does not have tables and records; it does not take SQL queries \
(although some people have made a SQL interface to it, the structure of the RRD does \
not lend itself to SQL readily).

Since the RRD contains 'RRA's which are roll-ups of posted data points and expired \
automatically over time, it is increasingly unlikely that you can retrieve a single \
data point value.  You will also not be able to retrieve the exact insert time due to \
the 'data normalisation' that brings the insert time in line with the 'time buckets' \
(eg rounding off to the next multiple of 5min).  Finally, there is no 'table name' or \
'db name' as such, though 'RRA' and 'RRD file' might be analagous.

For someone coming from a structured relational-database background, the RRD might \
appear to be horribly limited.  However, it is a highly specialised database \
structure optimised for a specific purpose which it performs very efficiently -- it \
should not be discounted because it cannot perform functions it was never intended \
for.

When making a graph generation call, you can of course pass any times you want for \
the start and end points (although whether or not the data are available in one of \
the RRAs at the required resolution is another matter).

Steve

Steve Shipway
ITS Unix Services Design Lead
University of Auckland, New Zealand
Floor 1, 58 Symonds Street, Auckland
Phone: +64 (0)9 3737599 ext 86487
DDI: +64 (0)9 924 6487
Mobile: +64 (0)21 753 189
Email: s.shipway@auckland.ac.nz
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