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store.go
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store.go
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package cachekv
import (
"bytes"
"io"
"sort"
"sync"
"github.com/tendermint/tendermint/libs/math"
dbm "github.com/tendermint/tm-db"
"github.com/cosmos/cosmos-sdk/internal/conv"
"github.com/cosmos/cosmos-sdk/store/listenkv"
"github.com/cosmos/cosmos-sdk/store/tracekv"
"github.com/cosmos/cosmos-sdk/store/types"
"github.com/cosmos/cosmos-sdk/types/kv"
)
// cValue represents a cached value.
// If dirty is true, it indicates the cached value is different from the underlying value.
type cValue struct {
value []byte
dirty bool
}
// Store wraps an in-memory cache around an underlying types.KVStore.
// If a cached value is nil but deleted is defined for the corresponding key,
// it means the parent doesn't have the key. (No need to delete upon Write())
type Store struct {
mtx sync.Mutex
cache map[string]*cValue
deleted map[string]struct{}
unsortedCache map[string]struct{}
sortedCache *dbm.MemDB // always ascending sorted
parent types.KVStore
}
var _ types.CacheKVStore = (*Store)(nil)
// NewStore creates a new Store object
func NewStore(parent types.KVStore) *Store {
return &Store{
cache: make(map[string]*cValue),
deleted: make(map[string]struct{}),
unsortedCache: make(map[string]struct{}),
sortedCache: dbm.NewMemDB(),
parent: parent,
}
}
// GetStoreType implements Store.
func (store *Store) GetStoreType() types.StoreType {
return store.parent.GetStoreType()
}
// Get implements types.KVStore.
func (store *Store) Get(key []byte) (value []byte) {
store.mtx.Lock()
defer store.mtx.Unlock()
types.AssertValidKey(key)
cacheValue, ok := store.cache[conv.UnsafeBytesToStr(key)]
if !ok {
value = store.parent.Get(key)
store.setCacheValue(key, value, false, false)
} else {
value = cacheValue.value
}
return value
}
// Set implements types.KVStore.
func (store *Store) Set(key []byte, value []byte) {
store.mtx.Lock()
defer store.mtx.Unlock()
types.AssertValidKey(key)
types.AssertValidValue(value)
store.setCacheValue(key, value, false, true)
}
// Has implements types.KVStore.
func (store *Store) Has(key []byte) bool {
value := store.Get(key)
return value != nil
}
// Delete implements types.KVStore.
func (store *Store) Delete(key []byte) {
store.mtx.Lock()
defer store.mtx.Unlock()
types.AssertValidKey(key)
store.setCacheValue(key, nil, true, true)
}
// Implements Cachetypes.KVStore.
func (store *Store) Write() {
store.mtx.Lock()
defer store.mtx.Unlock()
if len(store.cache) == 0 && len(store.deleted) == 0 && len(store.unsortedCache) == 0 {
store.sortedCache = dbm.NewMemDB()
return
}
// We need a copy of all of the keys.
// Not the best, but probably not a bottleneck depending.
keys := make([]string, 0, len(store.cache))
for key, dbValue := range store.cache {
if dbValue.dirty {
keys = append(keys, key)
}
}
sort.Strings(keys)
// TODO: Consider allowing usage of Batch, which would allow the write to
// at least happen atomically.
for _, key := range keys {
if store.isDeleted(key) {
// We use []byte(key) instead of conv.UnsafeStrToBytes because we cannot
// be sure if the underlying store might do a save with the byteslice or
// not. Once we get confirmation that .Delete is guaranteed not to
// save the byteslice, then we can assume only a read-only copy is sufficient.
store.parent.Delete([]byte(key))
continue
}
cacheValue := store.cache[key]
if cacheValue.value != nil {
// It already exists in the parent, hence delete it.
store.parent.Set([]byte(key), cacheValue.value)
}
}
// Clear the cache using the map clearing idiom
// and not allocating fresh objects.
// Please see https://bencher.orijtech.com/perfclinic/mapclearing/
for key := range store.cache {
delete(store.cache, key)
}
for key := range store.deleted {
delete(store.deleted, key)
}
for key := range store.unsortedCache {
delete(store.unsortedCache, key)
}
store.sortedCache = dbm.NewMemDB()
}
// CacheWrap implements CacheWrapper.
func (store *Store) CacheWrap() types.CacheWrap {
return NewStore(store)
}
// CacheWrapWithTrace implements the CacheWrapper interface.
func (store *Store) CacheWrapWithTrace(w io.Writer, tc types.TraceContext) types.CacheWrap {
return NewStore(tracekv.NewStore(store, w, tc))
}
// CacheWrapWithListeners implements the CacheWrapper interface.
func (store *Store) CacheWrapWithListeners(storeKey types.StoreKey, listeners []types.WriteListener) types.CacheWrap {
return NewStore(listenkv.NewStore(store, storeKey, listeners))
}
//----------------------------------------
// Iteration
// Iterator implements types.KVStore.
func (store *Store) Iterator(start, end []byte) types.Iterator {
return store.iterator(start, end, true)
}
// ReverseIterator implements types.KVStore.
func (store *Store) ReverseIterator(start, end []byte) types.Iterator {
return store.iterator(start, end, false)
}
func (store *Store) iterator(start, end []byte, ascending bool) types.Iterator {
store.mtx.Lock()
defer store.mtx.Unlock()
var parent, cache types.Iterator
if ascending {
parent = store.parent.Iterator(start, end)
} else {
parent = store.parent.ReverseIterator(start, end)
}
store.dirtyItems(start, end)
cache = newMemIterator(start, end, store.sortedCache, store.deleted, ascending)
return newCacheMergeIterator(parent, cache, ascending)
}
func findStartIndex(strL []string, startQ string) int {
// Modified binary search to find the very first element in >=startQ.
if len(strL) == 0 {
return -1
}
var left, right, mid int
right = len(strL) - 1
for left <= right {
mid = (left + right) >> 1
midStr := strL[mid]
if midStr == startQ {
// Handle condition where there might be multiple values equal to startQ.
// We are looking for the very first value < midStL, that i+1 will be the first
// element >= midStr.
for i := mid - 1; i >= 0; i-- {
if strL[i] != midStr {
return i + 1
}
}
return 0
}
if midStr < startQ {
left = mid + 1
} else { // midStrL > startQ
right = mid - 1
}
}
if left >= 0 && left < len(strL) && strL[left] >= startQ {
return left
}
return -1
}
func findEndIndex(strL []string, endQ string) int {
if len(strL) == 0 {
return -1
}
// Modified binary search to find the very first element <endQ.
var left, right, mid int
right = len(strL) - 1
for left <= right {
mid = (left + right) >> 1
midStr := strL[mid]
if midStr == endQ {
// Handle condition where there might be multiple values equal to startQ.
// We are looking for the very first value < midStL, that i+1 will be the first
// element >= midStr.
for i := mid - 1; i >= 0; i-- {
if strL[i] < midStr {
return i + 1
}
}
return 0
}
if midStr < endQ {
left = mid + 1
} else { // midStrL > startQ
right = mid - 1
}
}
// Binary search failed, now let's find a value less than endQ.
for i := right; i >= 0; i-- {
if strL[i] < endQ {
return i
}
}
return -1
}
type sortState int
const (
stateUnsorted sortState = iota
stateAlreadySorted
)
const minSortSize = 1024
// Constructs a slice of dirty items, to use w/ memIterator.
func (store *Store) dirtyItems(start, end []byte) {
startStr, endStr := conv.UnsafeBytesToStr(start), conv.UnsafeBytesToStr(end)
if end != nil && startStr > endStr {
// Nothing to do here.
return
}
n := len(store.unsortedCache)
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 < minSortSize {
for key := range store.unsortedCache {
// dbm.IsKeyInDomain is nil safe and returns true iff key is greater than start
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, stateUnsorted)
return
}
// Otherwise it is large so perform a modified binary search to find
// the target ranges for the keys that we should be looking for.
strL := make([]string, 0, n)
for key := range store.unsortedCache {
strL = append(strL, key)
}
sort.Strings(strL)
// Now find the values within the domain
// [start, end)
startIndex := findStartIndex(strL, startStr)
if startIndex < 0 {
startIndex = 0
}
var endIndex int
if end == nil {
endIndex = len(strL) - 1
} else {
endIndex = findEndIndex(strL, endStr)
}
if endIndex < 0 {
endIndex = len(strL) - 1
}
// Since we spent cycles to sort the values, we should process and remove a reasonable amount
// ensure start to end is at least minSortSize in size
// if below minSortSize, expand it to cover additional values
// this amortizes the cost of processing elements across multiple calls
if endIndex-startIndex < minSortSize {
endIndex = math.MinInt(startIndex+minSortSize, len(strL)-1)
if endIndex-startIndex < minSortSize {
startIndex = math.MaxInt(endIndex-minSortSize, 0)
}
}
kvL := make([]*kv.Pair, 0)
for i := startIndex; i <= endIndex; i++ {
key := strL[i]
cacheValue := store.cache[key]
kvL = append(kvL, &kv.Pair{Key: []byte(key), Value: cacheValue.value})
}
// kvL was already sorted so pass it in as is.
store.clearUnsortedCacheSubset(kvL, stateAlreadySorted)
}
func (store *Store) clearUnsortedCacheSubset(unsorted []*kv.Pair, sortState sortState) {
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)
}
} else { // Otherwise, normally delete the unsorted keys from the map.
for _, kv := range unsorted {
delete(store.unsortedCache, conv.UnsafeBytesToStr(kv.Key))
}
}
if sortState == stateUnsorted {
sort.Slice(unsorted, func(i, j int) bool {
return bytes.Compare(unsorted[i].Key, unsorted[j].Key) < 0
})
}
for _, item := range unsorted {
if item.Value == nil {
// deleted element, tracked by store.deleted
// setting arbitrary value
if err := store.sortedCache.Set(item.Key, []byte{}); err != nil {
panic(err)
}
continue
}
if err := store.sortedCache.Set(item.Key, item.Value); err != nil {
panic(err)
}
}
}
//----------------------------------------
// etc
// Only entrypoint to mutate store.cache.
func (store *Store) setCacheValue(key, value []byte, deleted bool, dirty bool) {
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[keyStr] = struct{}{}
}
}
func (store *Store) isDeleted(key string) bool {
_, ok := store.deleted[key]
return ok
}