with an active order, fee rates are requested each epoch

[chappjc]

2022-07-18 16:46:22.678 [DBG] CORE[dcr]: Retrieving fee rate from external API
2022-07-18 16:46:30.177 [DBG] CORE[dcr]: Retrieving fee rate from external API
2022-07-18 16:46:37.677 [DBG] CORE[dcr]: Retrieving fee rate from external API
2022-07-18 16:46:45.177 [DBG] CORE[dcr]: Retrieving fee rate from external API
2022-07-18 16:46:52.677 [DBG] CORE[dcr]: Retrieving fee rate from external API
2022-07-18 16:47:00.177 [DBG] CORE[dcr]: Retrieving fee rate from external API
2022-07-18 16:47:07.677 [DBG] CORE[dcr]: Retrieving fee rate from external API

The feeRate method in the above come from:

decred.org/dcrdex/client/asset/dcr.(*ExchangeWallet).FeeRate(0xc0002d97a0)
    /home/jon/github/decred/dcrdex/client/asset/dcr/dcr.go:878 +0x27
decred.org/dcrdex/client/core.(*Core).cacheRedemptionFeeSuggestion(0xc000322000, 0xc000170000)
    /home/jon/github/decred/dcrdex/client/core/core.go:7013 +0x53
decred.org/dcrdex/client/core.(*Core).tick(0xc000322000, 0xc000170000)
    /home/jon/github/decred/dcrdex/client/core/trade.go:1348 +0x189
decred.org/dcrdex/client/core.(*Core).listen.func3()
    /home/jon/github/decred/dcrdex/client/core/core.go:6476 +0x88a
decred.org/dcrdex/client/core.(*Core).listen.func4()
    /home/jon/github/decred/dcrdex/client/core/core.go:6506 +0x234
created by decred.org/dcrdex/client/core.(*Core).listen
    /home/jon/github/decred/dcrdex/client/core/core.go:6491 +0x3d0

I don't recall why, but cacheRedemptionFeeSuggestion calls the FeeRate method if the wallet is a FeeRater. If the wallet is a FeeRater, why does Core need to cache it's own suggestion? The issue seems to be in redeemMatchGroup where it atomic loads t.redeemFeeSuggestion but does not call FeeRate at all. We understandably want to avoid requesting fee rates in redeemMatchGroup, esp. if they are from remote sources, but we cannot call FeeRate on the ticker like we are doing now.

[chappjc]

Pursuing a resolution to this issue and https://github.com/decred/dcrdex/issues/1717. Rough plan, subject to change as I feel out the issues more:

• cacheRedemptionFeeSuggestion perhaps should not hit the wallet's FeeRate method since it is supposed to be caching the suggestion, not the wallet's own rate. This happens every epoch for every market for every order, and it is just too frequent. Alternatively, time stamp the cached fee, which also resolves a long-standing TODO to have the fee rate expire.
• (possibly) (*Core).redeemMatchGroup may call FeeRate if t.redeemFeeSuggestion is zero (no suggestion stored) Redeem is the one method that should still get a rate internally with the configured redeem conf target.
• modify FeeRaters with external API source fallback to cache that rate and put a limit on the frequency of external requests
• modify PreRedeem to only request a fee rate internally if the suggestion is 0. The caller should provide a feeRate like we do for the other wallet methods since https://github.com/decred/dcrdex/pull/1430
• apply several fixes to dcr's feeRateMethod https://github.com/decred/dcrdex/issues/1717#issuecomment-1188363018

[chappjc]

Resolution in https://github.com/decred/dcrdex/pull/1721

[chappjc]

Resolved by https://github.com/decred/dcrdex/pull/1721