Tests: No Cache Testing in ledger

[ahangsu]

Summary

Had a discussion with Pavel on disabling ledger LRU cache for testing purpose, we settled down on following design/implementation:

• Add a boolean field DisableLedgerLRUCache in Local (config/localTemplate.go)
• On accountUpdates/onlineAccounts initialize, maintain disableCache = cfg.DisableLedgerLRUCache.
• On accountUpdates/onlineAccounts initializeFromDisk, if !initializeFromDisk, init lrukv/lruaccts/lruresources/lruOnlineAccounts with pendingWrite = 0.
• Internal each LRU cache implementation, if pendingWrite == 0, set disableWrite* to be True.
• Internal each LRU cache implementation, if disableWrite* is True, then bypasses the write operation, such that it never writes into kvs (or map structure alike).

Test Plan

Need to design on testcase to confirm that it works...

• Unit test on 4 LRU implementation to make sure that disabling them will let no write into the cache.
• One manual negative test against accountUpdate in commit: f5f2af3, which confirmed that disabling LRU cache will lead to reading against DB, thus the test is indeed testing something.

[codecov]

Codecov Report

Merging #5058 (5954351) into master (6487b37) will increase coverage by 0.00%.
The diff coverage is 74.66%.

@@           Coverage Diff           @@
##           master    #5058   +/-   ##
=======================================
  Coverage   53.42%   53.42%           
=======================================
  Files         431      432    +1     
  Lines       54369    54412   +43     
=======================================
+ Hits        29046    29071   +25     
- Misses      23061    23079   +18     
  Partials     2262     2262           

Impacted Files	Coverage Δ
config/localTemplate.go	63.26% <ø> (ø)
ledger/ledger.go	70.09% <ø> (ø)
ledger/testing/withAndWithoutCache.go	0.00% <0.00%> (ø)
ledger/testing/consensusRange.go	23.07% <35.29%> (+23.07%)	⬆️
ledger/acctonline.go	78.86% <100.00%> (+0.22%)	⬆️
ledger/acctupdates.go	69.46% <100.00%> (+0.46%)	⬆️
ledger/lruaccts.go	92.45% <100.00%> (+2.86%)	⬆️
ledger/lrukv.go	94.59% <100.00%> (+0.84%)	⬆️
ledger/lruonlineaccts.go	94.59% <100.00%> (+0.84%)	⬆️
ledger/lruresources.go	92.85% <100.00%> (+2.66%)	⬆️
... and 12 more

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[ahangsu]

this is the place that will hit error, for first box (testcase[0]) goes into db after kvdelta:

• with LRU cache on, account-update reads from cache and still can get result, so it will not hit db read.
• otherwise, with nothing read from LRU cache and kvdelta, goes into DB and trigger panic.

[jannotti]

great. thanks for this sanity check.

[jannotti]

Had some minor comments, but I approve. Let me know when you want it merged.

[ahangsu]

Thanks for the previous approval @jannotti !

Let's see if I can get Chris approving it tomorrow, then we merge with 2 approvals.