Re: [pcp] braindump on unified-context / live-logging

[Greg Banks <gbanks@xxxxxxx>]

On 13/01/14 16:07, Max Matveev wrote:
> On Mon, 13 Jan 2014 14:19:26 -0800, Greg Banks wrote:
>
>   gnb> While I designed and wrote the thing, I was never happy with any
>   gnb> of the iterations of the architecture and I wouldn't recommend
>   gnb> to anyone that they copy it. Some of the problems were:
>
>   gnb>   * it was both a client of pmcd and a PMDA, which led to interesting
>   gnb> deadlocks with the single-threaded pmcd
>
> That was the "second" pass with nasavg pmda. I thought there was a
> first version which only used archives but it had to be abandoned
> because tailing of archive being written wasn't working reliably.
Yes, the first design iteration tailed archives and was horribly 
unreliable.  Pmarchive was writing to the various files of an archive in 
such a way that there was a race window where the archive reading code 
in libpcp would see an inconsistent archive and barf. Plus, there was an 
inconvenient amount of lag, up to 30 seconds, in pmarchive and in the 
tailer.
--
Greg.