Sorry for the flashy title. I was looking at a combat log for an unrelated bug (DK's Army of the Dead not triggering SPELL_SUMMON) and decided to do the combat log load analysis I wanted to do since recently people started reporting combat log related performance problems.
To make the main story short. In a patchwerk combat log lasting 07:35 and containing a total of 51615 combat log lines, I found a total of 10856 lines solely because of the Rampage talent (SPELL_AURA_APPLIED, SPELL_AURA_REMOVED). Which is over 1/5 of all events total (i.e. one talent does 21% of all combat log events at Patchwerk).
What makes matters worse is that it's bursty. A Rampage triggers while another is up will cause two combat log lines per raid member in 45 yards. First the old Aura is removed, then the new applied, leading of a total of 2*25=50 combat log events instantly.
While other aura or energy gain things can be fairly bursty (Replenishes or an Aura kicking in that overrides another, also causing 50 cascades), it's the sheer frequency of Rampage that makes it this huge.
Cascading aura remove/applies seem to be the sole reason for bursty combat log. I found no other pattern that can lead to 50+ events during one time signature.
For comparison Mana Spring Totem is responsible for 3443 (or 6.5%) and Replenishment are responsible for 2865 (or 5.5%) of combat log events in the same fight.
On the event side, SPELL_AURA_REFRESH with 11628 is most frequent. Followed by SPELL_PERIODIC_ENERGY at 7717, SPELL_AURA_APPLIED with 7261 and SPELL_AURA_REMOVED with 7146. This means that AURA related events make up 50.4% of all combat log events and Rampage alone is not quite managing to be half of that.
SPELL_PERIODIC_ENERGY (mostly from Mana spring + replenishment) could be a concern too but the mana spring count has to do with 5 shamans being present which is atypical. Mana spring doesn't not function raid wide and hence this contribution will scale down in more typical settings.
For comparison SPELL_DAMAGE at 3698, SPELL_CAST_SUCCESS at 2154, SPELL_HEAL at 1562, SPELL_PERIODIC_DAMAGE at 1858, SPELL_PERIODIC_HEAL at 2066, SWING_DAMAGE at 2510.
I think the problem with auras and Rampage in particular is that it's (a) raid-wide, and (b) on a high proc, i.e. very likely to trigger frequently for many people. Other combat log events are localized to one or few targets or happen rarely (like rebuffs). Energy gains do happen frequently and could become a similar load factor, as we see already.
The burstiness to the combat log of raid-wide effects is concerning regardless. 50 combat log events because an aura gets reapplied all at one time seems a fairly hefty load if it happens alongside normal log volumes. This is of course worse for Wintergrasp raids were we talk up to 40 people and hence 80 events in response to one action or proc.
The party had two fury warriors but no LotP from a feral druid. A feral druid would take the edge off here, because these do not stack and LotP should prevent aura-restacks hence remove 20% of combat log events here (this would need a test to verify).
This is interesting... With the massive lag that afflict the raid instances on some realms, I wonder if cutting 20% of the volume of combat log might reduce server load (in current state I imagine most raid parties have at least one fury warrior)...
Have you posted that on the official forums ?
I'm in Europe, meaning whatever I post on my accessible forums I have no clue if it ever gets read by Blizz, experience shows that UI based feedback there tends to get lost. But my plan was to put this up for discussion first and once there is some consensus bring it to Blizz.
This is interesting indeed. I think it is valid to ask if the verbosity of the combat log has increased or decreased any amount of data sent between the server/client in the first place, because if the answer is no, then it isn't really valid to argue that Rampage is overloading servers.
I do suspect this is unintentional. WotLK did bring more combat log events without a doubt, because a lot of things that used to be party wide are now raid wide. Take replenishments. In the past this was just a group wide shadow priest thing. Now it's raid wide. Factor: combat log contribution: 5.
Now Rampage is special because it procs to reapply buffs. A lot of other buffs are just refreshed when buffed before the encounter or when in a certain form/stance/aura. With a 10 second duration and the ability to proc on every crit and affecting everybody in 45 yards it's kind of asking for a lot of traffic. I would argue that Rampage sent to the client must have a higher volume due to the raid wide effect. It used to be group wide only (pre 3.0.2) and in fact limited to 20 yards (pre 3.0.3 I think).
Basically it's an update sent to virtually every raid member on every melee crit of a fury warrior, causing 50 combat log events per crit. This includes specials crits, in fact for 3.0.3 WW offhand crits were fixed to proc this.
It's meant to be a substitute for LotP so not surprising that it's intended to be up most of the time, but the mechanism makes it massively spammy for the combatlog.