perf: Make CacheKV store interleaved iterator and insertion not O(n^2) (backport #10026) (#10167)

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

(cherry picked from commit 28bf2c1)

# Conflicts:
#	CHANGELOG.md
#	store/cachekv/store.go

* fix changelog conflict

* Update store.go

Co-authored-by: Dev Ojha <[email protected]>
Co-authored-by: Robert Zaremba <[email protected]>

Author: 3 people

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/memiterator.go

@@ -1,107 +1,50 @@
 package cachekv
 
 import (
-	"errors"
-
 	dbm "github.com/tendermint/tm-db"
 
-	"github.com/cosmos/cosmos-sdk/types/kv"
+	"github.com/cosmos/cosmos-sdk/store/types"
 )
 
 // Iterates over iterKVCache items.
 // if key is nil, means it was deleted.
 // Implements Iterator.
 type memIterator struct {
-	start, end []byte
-	items      []*kv.Pair
-	ascending  bool
-}
-
-func newMemIterator(start, end []byte, items *kv.List, ascending bool) *memIterator {
-	itemsInDomain := make([]*kv.Pair, 0, items.Len())
-
-	var entered bool
-
-	for e := items.Front(); e != nil; e = e.Next() {
-		item := e.Value
-		if !dbm.IsKeyInDomain(item.Key, start, end) {
-			if entered {
-				break
-			}
-
-			continue
-		}
-
-		itemsInDomain = append(itemsInDomain, item)
-		entered = true
-	}
+	types.Iterator
 
-	return &memIterator{
-		start:     start,
-		end:       end,
-		items:     itemsInDomain,
-		ascending: ascending,
-	}
+	deleted map[string]struct{}
 }
 
-func (mi *memIterator) Domain() ([]byte, []byte) {
-	return mi.start, mi.end
-}
+func newMemIterator(start, end []byte, items *dbm.MemDB, deleted map[string]struct{}, ascending bool) *memIterator {
+	var iter types.Iterator
+	var err error
 
-func (mi *memIterator) Valid() bool {
-	return len(mi.items) > 0
-}
+	if ascending {
+		iter, err = items.Iterator(start, end)
+	} else {
+		iter, err = items.ReverseIterator(start, end)
+	}
 
-func (mi *memIterator) assertValid() {
-	if err := mi.Error(); err != nil {
+	if err != nil {
 		panic(err)
 	}
-}
 
-func (mi *memIterator) Next() {
-	mi.assertValid()
-
-	if mi.ascending {
-		mi.items = mi.items[1:]
-	} else {
-		mi.items = mi.items[:len(mi.items)-1]
+	newDeleted := make(map[string]struct{})
+	for k, v := range deleted {
+		newDeleted[k] = v
 	}
-}
 
-func (mi *memIterator) Key() []byte {
-	mi.assertValid()
+	return &memIterator{
+		Iterator: iter,
 
-	if mi.ascending {
-		return mi.items[0].Key
+		deleted: newDeleted,
 	}
-
-	return mi.items[len(mi.items)-1].Key
 }
 
 func (mi *memIterator) Value() []byte {
-	mi.assertValid()
-
-	if mi.ascending {
-		return mi.items[0].Value
-	}
-
-	return mi.items[len(mi.items)-1].Value
-}
-
-func (mi *memIterator) Close() error {
-	mi.start = nil
-	mi.end = nil
-	mi.items = nil
-
-	return nil
-}
-
-// Error returns an error if the memIterator is invalid defined by the Valid
-// method.
-func (mi *memIterator) Error() error {
-	if !mi.Valid() {
-		return errors.New("invalid memIterator")
+	key := mi.Iterator.Key()
+	if _, ok := mi.deleted[string(key)]; ok {
+		return nil
 	}
-
-	return nil
+	return mi.Iterator.Value()
 }

store/cachekv/store.go

@@ -20,17 +20,17 @@ import (
 // If value is nil but deleted is false, it means the parent doesn't have the
 // key.  (No need to delete upon Write())
 type cValue struct {
-	value   []byte
-	deleted bool
-	dirty   bool
+	value []byte
+	dirty bool
 }
 
 // Store wraps an in-memory cache around an underlying types.KVStore.
 type Store struct {
 	mtx           sync.Mutex
 	cache         map[string]*cValue
+	deleted       map[string]struct{}
 	unsortedCache map[string]struct{}
-	sortedCache   *kv.List // always ascending sorted
+	sortedCache   *dbm.MemDB // always ascending sorted
 	parent        types.KVStore
 }
 
@@ -40,8 +40,9 @@ var _ types.CacheKVStore = (*Store)(nil)
 func NewStore(parent types.KVStore) *Store {
 	return &Store{
 		cache:         make(map[string]*cValue),
+		deleted:       make(map[string]struct{}),
 		unsortedCache: make(map[string]struct{}),
-		sortedCache:   kv.NewList(),
+		sortedCache:   dbm.NewMemDB(),
 		parent:        parent,
 	}
 }
@@ -122,7 +123,7 @@ func (store *Store) Write() {
 		cacheValue := store.cache[key]
 
 		switch {
-		case cacheValue.deleted:
+		case store.isDeleted(key):
 			store.parent.Delete([]byte(key))
 		case cacheValue.value == nil:
 			// Skip, it already doesn't exist in parent.
@@ -133,8 +134,9 @@ func (store *Store) Write() {
 
 	// Clear the cache
 	store.cache = make(map[string]*cValue)
+	store.deleted = make(map[string]struct{})
 	store.unsortedCache = make(map[string]struct{})
-	store.sortedCache = kv.NewList()
+	store.sortedCache = dbm.NewMemDB()
 }
 
 // CacheWrap implements CacheWrapper.
@@ -178,23 +180,40 @@ func (store *Store) iterator(start, end []byte, ascending bool) types.Iterator {
 	}
 
 	store.dirtyItems(start, end)
-	cache = newMemIterator(start, end, store.sortedCache, ascending)
+	cache = newMemIterator(start, end, store.sortedCache, store.deleted, ascending)
 
 	return newCacheMergeIterator(parent, cache, ascending)
 }
 
 // Constructs a slice of dirty items, to use w/ memIterator.
 func (store *Store) dirtyItems(start, end []byte) {
-	unsorted := make([]*kv.Pair, 0)
-
 	n := len(store.unsortedCache)
-	for key := range store.unsortedCache {
-		if dbm.IsKeyInDomain(conv.UnsafeStrToBytes(key), start, end) {
+	unsorted := make([]*kv.Pair, 0)
+	// If the unsortedCache is too big, its costs too much to determine
+	// whats in the subset we are concerned about.
+	// If you are interleaving iterator calls with writes, this can easily become an
+	// O(N^2) overhead.
+	// Even without that, too many range checks eventually becomes more expensive
+	// than just not having the cache.
+	if n >= 1024 {
+		for key := range store.unsortedCache {
 			cacheValue := store.cache[key]
 			unsorted = append(unsorted, &kv.Pair{Key: []byte(key), Value: cacheValue.value})
 		}
+	} 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)
+}
 
+func (store *Store) clearUnsortedCacheSubset(unsorted []*kv.Pair) {
+	n := len(store.unsortedCache)
 	if len(unsorted) == n { // This pattern allows the Go compiler to emit the map clearing idiom for the entire map.
 		for key := range store.unsortedCache {
 			delete(store.unsortedCache, key)
@@ -204,32 +223,21 @@ func (store *Store) dirtyItems(start, end []byte) {
 			delete(store.unsortedCache, conv.UnsafeBytesToStr(kv.Key))
 		}
 	}
-
 	sort.Slice(unsorted, func(i, j int) bool {
 		return bytes.Compare(unsorted[i].Key, unsorted[j].Key) < 0
 	})
 
-	for e := store.sortedCache.Front(); e != nil && len(unsorted) != 0; {
-		uitem := unsorted[0]
-		sitem := e.Value
-		comp := bytes.Compare(uitem.Key, sitem.Key)
-
-		switch comp {
-		case -1:
-			unsorted = unsorted[1:]
-
-			store.sortedCache.InsertBefore(uitem, e)
-		case 1:
-			e = e.Next()
-		case 0:
-			unsorted = unsorted[1:]
-			e.Value = uitem
-			e = e.Next()
+	for _, item := range unsorted {
+		if item.Value == nil {
+			// deleted element, tracked by store.deleted
+			// setting arbitrary value
+			store.sortedCache.Set(item.Key, []byte{})
+			continue
+		}
+		err := store.sortedCache.Set(item.Key, item.Value)
+		if err != nil {
+			panic(err)
 		}
-	}
-
-	for _, kvp := range unsorted {
-		store.sortedCache.PushBack(kvp)
 	}
 }
 
@@ -238,12 +246,22 @@ func (store *Store) dirtyItems(start, end []byte) {
 
 // Only entrypoint to mutate store.cache.
 func (store *Store) setCacheValue(key, value []byte, deleted bool, dirty bool) {
-	store.cache[conv.UnsafeBytesToStr(key)] = &cValue{
-		value:   value,
-		deleted: deleted,
-		dirty:   dirty,
+	keyStr := conv.UnsafeBytesToStr(key)
+	store.cache[keyStr] = &cValue{
+		value: value,
+		dirty: dirty,
+	}
+	if deleted {
+		store.deleted[keyStr] = struct{}{}
+	} else {
+		delete(store.deleted, keyStr)
 	}
 	if dirty {
 		store.unsortedCache[conv.UnsafeBytesToStr(key)] = struct{}{}
 	}
 }
+
+func (store *Store) isDeleted(key string) bool {
+	_, ok := store.deleted[key]
+	return ok
+}