Re: [patch][4.0.0alpha3] switch to cmdSystemOrEvalLong in BackupPC_rrdUpdate

10.12.2013 21:30, Tyler J. Wagner пишет:
> On 2013-12-10 11:22, Alexander Moisseev wrote:
>> By the way, you change the CF type of an RRA from AVERAGE in V3 to LAST in V4alpha3.
>> I think that conversion of the CF type of RRA is very hard (or may be impossible).
>
> It is not possible. If you consolidate the data as AVERAGE, the LAST data
> is lost. You can begin consolidating new data as LAST, but the older data
> will show the AVERAGE data (and you'll mistakenly think it is LAST). This
> isn't a big issue, as AVERAGE and LAST are usually similar. It's a big
> problem when you want to keep MIN/MAX data and it's not available.
>
I meant "very hard (or may be impossible)" with available tools. In our case consolidation interval equal to 1, therefore consolidated data numerically equal regardless of CF. We can't convert database on the fly with rrdtool or some known Perl module, but we can dump database, edit as needed and restore back (or fetch data, create new database and fill it with old data) without data loss.

> However, RRDs are small!* There is no need to throw away the AVERAGE data.
> We can store both AVERAGE and LAST (and MIN and MAX if we want) in the same
> RRD file. Most Cacti installs keep 2-4 sets of consolidated data in this way.
>
Adding new RRA or DS to existing RRD relatively easy, but what to do next? Hypothetically (I don't really know), we can draw graphs of both old and new RRA on same picture, and may be some how calculate current/average/maximum value for a legend.

When I wrote the code, I decided to add new DSes and leave RRA format as is to avoid database conversion. Since we about to change RRD format, I propose discuss it.

I suppose we would add separate RRA for 52 week graph to properly consolidate data. I am not sure about CF. AVERAGE or MAX? Another way is to use DEF with :reduce=<CF> option (consolidation on the fly).

Craig, you create RRA with 732 data points. Do you have some intentions about usage of 2 year data in the future?


About V3 to V4 rrd upgrade script. Craig, I guess you want to include it in configure.pl? Please, don't do it. Nowadays many users install software from packages rather then source or ports. In case of package, configure.pl runs on machine where package builds (e.g. OS vendor build cluster) at package build time. So package always contain config files with default options. It's OK for new installations, but if user doing an upgrade he/she must edit configuration files by hand or install BackupPC from sources/port (or build himself package on production server then install).
Ideally instead of single configure.pl we need separate install and postinstall scripts. Postinstall script should do all upgrade procedures: make changes in configuration files, database conversion and so on.

--
Alexander


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