perf: Make CacheKV store interleaved iterator and insertion not O(n^2…

…) (backport cosmos#10026) (cosmos#10167)

* perf: Make CacheKV store interleaved iterator and insertion not O(n^2) (cosmos#10026)

(cherry picked from commit 28bf2c1)

* fix changelog conflict

* Update store.go

Co-authored-by: Dev Ojha <ValarDragon@users.noreply.github.com>
Co-authored-by: Robert Zaremba <robert@zaremba.ch>

CHANGELOG.md

@@ -38,7 +38,9 @@ Ref: https://keepachangelog.com/en/1.0.0/
 ## [Unreleased]
 
 ### Improvements
+
 * (types) [\#10021](https://github.com/cosmos/cosmos-sdk/pull/10021) Speedup coins.AmountOf(), by removing many intermittent regex calls.
+* (store) [\#10026](https://github.com/cosmos/cosmos-sdk/pull/10026) Improve CacheKVStore datastructures / algorithms, to no longer take O(N^2) time when interleaving iterators and insertions.
 
 ### Bug Fixes
 

store/cachekv/store.go

@@ -260,7 +260,17 @@ func findEndIndex(strL []string, endQ string) int {
 		} else { // midStrL > startQ
 			right = mid - 1
 		}
+	} else {
+		// else do a linear scan to determine if the unsorted pairs are in the pool.
+		for key := range store.unsortedCache {
+			if dbm.IsKeyInDomain(conv.UnsafeStrToBytes(key), start, end) {
+				cacheValue := store.cache[key]
+				unsorted = append(unsorted, &kv.Pair{Key: []byte(key), Value: cacheValue.value})
+			}
+		}
 	}
+	store.clearUnsortedCacheSubset(unsorted)
+}
 
 	// Binary search failed, now let's find a value less than endQ.
 	for i := right; i >= 0; i-- {