[rrd-users] Fetch the time of the first entry

[Simon Hobson]

Steven Sim <unixandme at outlook.com> wrote:

> When I create the RRD, I am forced to give the --start <TIME> as one step BEHIND my actual update.
> 
> So let's say my data starts at midnight 1st July, I am forced to create a RRD with --start time at 11:45 30th of June.
> 
> data starts -> 1st July 00:00:00 <-- first data entry.
> Step = 15 minutes (900 seconds)
> RRD has to be created with --start 11:45 30th of June (one step behind).
> 
> if I do not create it 1 step behind, I get an error with my updates.

This came up recently. In effect, the START parameter sets the last update time for the RRD, as you can't have two updates with the same time, you need to set the start parameter to before the timestamp of your first update.
In principal the actual value doesn't matter - it could even be 0. However, if it's "a long time ago" then on your first update, RRD will have to roll forward and process all the non-existant updates to get up to date. How this came up was someone found that if they had no updates for a few days (machine down) then they found the first update took a lot longer than normal.