pm: lower avgGasPrice

[leszko]

What does this pull request do? Explain your changes. (required)

Lower the hardcoded avg gas price to prevent Os from dropping streams in case of the gas price spikes.

The value is changed from 200 => 140. Here's the rationale why this value was chosen. In our problematic scenario, in the case when maxFaceValue is not set, then:

1. In order to not drop the stream during gas spike this condition faceValue.Cmp(r.txCostWithGasPrice(avgGasPrice)) < 0 must be false
2. In the worse case scenario, face value equals to max float (which corresponds to the B's reserve, currently 180000000000000000)
3. txCostWithGasPrice() is calculated as redeemGas * avgGasPrice, where Arbitrum redeemGas is hardcoded as 1200000
4. That means that 180000000000000000 < 1200000 * avgGasPrice must be false
5. That means that 180000000000000000 >= 1200000 * avgGasPrice must be true
6. That means that avgGasPrice <= 180000000000000000 / 1200000 => avgGasPrice <= 150000000000

So, with the current B's reserve and the current hardcoded redeemGas, the avgGasPrice must be smaller than 150 Gwei. To make a buffer, I changed it to 140.

Specific updates (required)

• Change avgGasPrice
• Simplify the condition check

How did you test each of these updates (required)

Debugged with Orchestrator.

Does this pull request close any open issues?

fix #2473

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[codecov]

Codecov Report

Merging #2481 (c14d9ce) into master (159deaa) will decrease coverage by 0.02337%.
The diff coverage is 33.33333%.

@@                 Coverage Diff                 @@
##              master       #2481         +/-   ##
===================================================
- Coverage   54.70159%   54.67822%   -0.02337%     
===================================================
  Files             95          95                 
  Lines          19855       19858          +3     
===================================================
- Hits           10861       10858          -3     
- Misses          8390        8396          +6     
  Partials         604         604                 

Impacted Files	Coverage Δ
cmd/livepeer/starter/starter.go	2.29008% <0.00000%> (-0.00657%)	⬇️
pm/recipient.go	89.63964% <100.00000%> (ø)
discovery/db_discovery.go	67.01389% <0.00000%> (-1.04167%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2757289...c14d9ce. Read the comment docs.

[yondonfu]

Just to clarify my own understanding (I wrote this avgGasPrice check awhile ago, but I need to jog my memory around how it works...):

avgGasPrice is supposed to represent the average gas price during a period of time. For simplicity, it was originally hardcoded to 200 gwei which indicates that the average gas price is 200 gwei (which was probably accurate at some point on L1).

The check faceValue.Cmp(r.txCostWithGasPrice(avgGasPrice)) < 0 is used as a secondary check when faceValue < txCost where txCost is calculated based on the current estimated gas price. The reason for having this secondary check is that when faceValue < txCost it might be the case that we are in the middle of a gas price spike which is why faceValue < txCost. If we are in the middle of a gas price spike it would be reasonable to expect the gas price to fall after a period of time. As long as the faceValue can cover the expected tx cost based on avgGasPrice (recall that this is meant to represent the average gas price) then O advertises ticket params assuming that the gas price will fall to avgGasPrice or lower.

With this in mind, it makes sense that a lower avgGasPrice makes sense here because the average gas price on Arbitrum is substantially lower than 200 gwei. In reality, the average gas price is even lower than 140 gwei (I know that the OP describes deriving this value based on an assumption of the value of B's reserve, but I generally don't think we should hardcoded values based on an assumption of the value of B's reserve).

I think this PR is fine as-is though as the more ideal solution is to not hardcode a value for avgGasPrice at all which can be followed up on.

[yondonfu]

Minor comment about fixing an outdated comment.

Other than that LGTM.

[yondonfu]

Let's update this comment

[leszko]

Updated in 98cad6d

[leszko]

Just to clarify my own understanding (I wrote this avgGasPrice check awhile ago, but I need to jog my memory around how it works...):

avgGasPrice is supposed to represent the average gas price during a period of time. For simplicity, it was originally hardcoded to 200 gwei which indicates that the average gas price is 200 gwei (which was probably accurate at some point on L1).

The check faceValue.Cmp(r.txCostWithGasPrice(avgGasPrice)) < 0 is used as a secondary check when faceValue < txCost where txCost is calculated based on the current estimated gas price. The reason for having this secondary check is that when faceValue < txCost it might be the case that we are in the middle of a gas price spike which is why faceValue < txCost. If we are in the middle of a gas price spike it would be reasonable to expect the gas price to fall after a period of time. As long as the faceValue can cover the expected tx cost based on avgGasPrice (recall that this is meant to represent the average gas price) then O advertises ticket params assuming that the gas price will fall to avgGasPrice or lower.

With this in mind, it makes sense that a lower avgGasPrice makes sense here because the average gas price on Arbitrum is substantially lower than 200 gwei. In reality, the average gas price is even lower than 140 gwei (I know that the OP describes deriving this value based on an assumption of the value of B's reserve, but I generally don't think we should hardcoded values based on an assumption of the value of B's reserve).

I think this PR is fine as-is though as the more ideal solution is to not hardcode a value for avgGasPrice at all which can be followed up on.

Yes, everything you described is correct. You may be right that we should maybe not make any assumptions about our B reserve. So how, about setting average gas price to some more realistic number in Arbitrum, like 2 or 3. Wdyt?

[yondonfu]

So how, about setting average gas price to some more realistic number in Arbitrum, like 2 or 3. Wdyt?

👍

[leszko]

So how, about setting average gas price to some more realistic number in Arbitrum, like 2 or 3. Wdyt?

👍

Updated in 98cad6d