Monday, February 14, 2011

Mana Liquidity

In a previous post I said that Discipline Priests were in the position of usually having enough mana to do the healing they needed to do over the course of the fight, but not having the throughput to actually apply that mana to remedy bad situations. Pach 4.0.6 changed that. Discipline priests now have the ability to have an all out mana fire sale, shipping our mana off in massive quantities for whatever healing we can get.

Before I get into that, I want to look at the question of how to understand spending more mana to do more healing. Given a fixed fight length you generally find yourself with a certain amount of mana to spend. In the case of a discipline priest and a 5 minute fight, that amount of mana might be in the neighborhood of 450k to 490k (plus about 40k per resto shaman in the raid). In a fight of that length you will probably be called on to do something like 2.5M healing, meaning you'll need to average between 5 and 5.5 healing per mana to get there.

A simple single target rotation of Shield -> Penance -> Renew (when Borrowed Time is up) -> Inner Focus -> Greater Heal gives 6.92 mana effiency, more than enough to do the job. With a rotation like this, you'll spend only 361k mana doing 2.5M healing, leaving you with something like 130k mana to play with. The question is, how quickly can you liquidate your mana into healing when you need to?

There are two ways to spend more mana: cast more often or cast more expensive things when you are casting. If we are sticking with a simple single target healing model then casting more often probably isn't a legitimate option. While no one is casting all the time, we are generally casting at all times when we are able and when healing is needed. Running out of a fire might cost us healing time, and a phase transition where no damage is incoming might also cost us healing time.

So today I am going to talk about replacing our existing casting time with more mana intense casting time. I hope to come back to this subject tomorrow or the next day with comments about casting more during downtime.

Discipline now has the Shield -> Flash Heal x3 rotation available. The ability to cast a Power Word: Shield every 5.3 seconds makes for some pretty extreme throughput. Using just Flash of Heal and Shield in 359s you can achieve a throughput of 19.7k, but at the cost of around 4360 mana per second, 2100 more healing per mana than the baseline rotation. For that extra mana you get 4130 more healing per second. You are buying extra healing at a rate of 1.97 healing per mana.

If you use the slightly less insane rotation of incorporating Penance when it is off cooldown, you can buy 3670 healing per second for around 2.23 healing per mana. If you incorporate Renew you get only 3250 extra healing per second but actually only get 2.19 healing per mana, so this is not recommended.

Given the high cost of these rotations, it stands to ask how long we actually afford them. With the 130k unused mana, Shield/Flash could replace the baseline rotation for up to 61 seconds. That actually sounds like an awful lot. If you are casting 90% of the time then you could afford to be on all out mana destruction mode for almost a quarter of the time that you are casting.

So can this tell us anything about how to value Spirit compared to throughput stats?

Using this model, we can calculate how much more healing we can expect to get out of various stats. Of course there are two ways to approach it. One is to fix the amount of time you have to heal and calculate how much more healing you can squeeze out in that time with more of a stat. Another is to fix the amount you need to heal and see how much mana you have left over.

Using either of these methods generates fairly similar results. With fixed healing time, we get Mastery > Crit > Spirit at 36%, 28%, 20% of an Intellect respectively. With fixed healing to be done we get the same order but closer together in the raw amounts at 33%, 27%, 26% respectively.

This model has a lot of deficiencies, and should not be applied as a stat weighting. My hope is that by doing calculations like this I can get a better sense of how Spirit interacts with the other secondary stats. These results can only be narrowly applied, but could suggest that if you find you have enough mana to get through fights, you should consider moving some of your spirit into mastery to increase your ability to deal with difficult situations. They also make me fairly comfortable that mastery is the better choice than crit for improving my throughput, but that could change as I go through more examples.

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