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From Rainer Jung <rainer.j...@kippdata.de>
Subject Re: Balancer Persist testing
Date Fri, 14 Dec 2012 13:36:04 GMT
On 14.12.2012 13:39, Jim Jagielski wrote:
> 
> On Dec 14, 2012, at 7:10 AM, Rainer Jung <rainer.jung@kippdata.de> wrote:
>>
>> - The "Used" count in balancer manager drops to "0" after restart/reboot
>> with persist on. It seems the slot management is not completely right.
>> Not yet further investigated.
> 
> This is intentional actually. The configs are maintained, but
> the stats are not, since we must start the "counting" from
> scratch since the config has changed.

Note that "Used" isn't the request count. It is the number of slots
already occupied with data (so typically it shows the number of members
of the balancer). If dropping it to "0" after restart is intended,
what's the meaning of the field then?

>> - A warning might be needed about mixing changes via balancer manager
>> and via config:
>>
>>  - If changing the path for a balancer in config while persist is on
>>    and then restarting, the balancer manager shows the old path
>>    from the persisted shm, but it seems the new one from the
>>    config is in effect.
>>
>>  - E.g. setting a member state to stopped in config and again doing
>>    a persist restart, the old state from shm wins and the change in
>>    config is ignored.
>>
> +1
> 
>> So it seems before applying changes to the config one should always
>> backport all changes applied via the manager (not trivial, because you'd
>> have to check all displayed values against the configured ones), then
>> stop, then remove the *.persist files, apply config changes and start again.
>>
>> - Switching persistence from on to off in config and then doing a
>> restart keeps the old .persist files around. They are ignored during the
>> startup as expected, but next time you'll switch back to persist on, the
>> outdated .persist file will again be loaded.
>>
> 
> Yeah, good point...
> 
>> - "Elected" display in balancer manager survives restart, whereas
>>  "To" and "From" (byte counts) do not.
>>
> 
> Again intentional.

>From the above I got the impression you wanted to not persist stats. So
why not also drop "Elected"? Is it, because "Elected" by itself is never
used for a balancing decision, whereas "From" and "To" are in case
"bytraffic" is used? Then I would understand the reason technically, but
for users it will be a bit confusing to persist the number of requests
but not the traffic. I would then prefer to not persist the number of
requests as well. Otherwise the data shown after restart is inconsistent.

Very nice feature, but hard to get it right!

Regards,

Rainer


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