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230 lines
5.1 KiB
230 lines
5.1 KiB
package db
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import (
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"fmt"
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"sort"
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"sync"
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"sync/atomic"
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)
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// If value is nil but deleted is false,
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// it means the parent doesn't have the key.
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// (No need to delete upon Write())
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type cDBValue struct {
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value []byte
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deleted bool
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dirty bool
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}
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// CacheDB wraps an in-memory cache around an underlying DB.
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type CacheDB struct {
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mtx sync.Mutex
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cache map[string]cDBValue
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parent DB
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lockVersion interface{}
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cwwMutex
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}
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// Needed by MultiStore.CacheWrap().
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var _ atomicSetDeleter = (*CacheDB)(nil)
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// Users should typically not be required to call NewCacheDB directly, as the
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// DB implementations here provide a .CacheWrap() function already.
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// `lockVersion` is typically provided by parent.GetWriteLockVersion().
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func NewCacheDB(parent DB, lockVersion interface{}) *CacheDB {
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db := &CacheDB{
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cache: make(map[string]cDBValue),
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parent: parent,
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lockVersion: lockVersion,
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cwwMutex: NewCWWMutex(),
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}
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return db
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}
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func (db *CacheDB) Get(key []byte) []byte {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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dbValue, ok := db.cache[string(key)]
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if !ok {
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data := db.parent.Get(key)
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dbValue = cDBValue{value: data, deleted: false, dirty: false}
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db.cache[string(key)] = dbValue
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}
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return dbValue.value
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}
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func (db *CacheDB) Set(key []byte, value []byte) {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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db.SetNoLock(key, value)
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}
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func (db *CacheDB) SetSync(key []byte, value []byte) {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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db.SetNoLock(key, value)
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}
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func (db *CacheDB) SetNoLock(key []byte, value []byte) {
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db.cache[string(key)] = cDBValue{value: value, deleted: false, dirty: true}
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}
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func (db *CacheDB) Delete(key []byte) {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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db.DeleteNoLock(key)
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}
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func (db *CacheDB) DeleteSync(key []byte) {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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db.DeleteNoLock(key)
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}
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func (db *CacheDB) DeleteNoLock(key []byte) {
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db.cache[string(key)] = cDBValue{value: nil, deleted: true, dirty: true}
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}
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func (db *CacheDB) Close() {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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db.parent.Close()
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}
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func (db *CacheDB) Print() {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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fmt.Println("CacheDB\ncache:")
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for key, value := range db.cache {
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fmt.Printf("[%X]:\t[%v]\n", []byte(key), value)
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}
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fmt.Println("\nparent:")
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db.parent.Print()
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}
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func (db *CacheDB) Stats() map[string]string {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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stats := make(map[string]string)
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stats["cache.size"] = fmt.Sprintf("%d", len(db.cache))
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stats["cache.lock_version"] = fmt.Sprintf("%v", db.lockVersion)
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mergeStats(db.parent.Stats(), stats, "parent.")
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return stats
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}
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func (db *CacheDB) Iterator() Iterator {
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panic("CacheDB.Iterator() not yet supported")
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}
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func (db *CacheDB) NewBatch() Batch {
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return &memBatch{db, nil}
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}
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// Implements `atomicSetDeleter` for Batch support.
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func (db *CacheDB) Mutex() *sync.Mutex {
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return &(db.mtx)
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}
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// Write writes pending updates to the parent database and clears the cache.
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func (db *CacheDB) Write() {
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db.mtx.Lock()
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defer db.mtx.Unlock()
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// Optional sanity check to ensure that CacheDB is valid
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if parent, ok := db.parent.(WriteLocker); ok {
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if parent.TryWriteLock(db.lockVersion) {
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// All good!
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} else {
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panic("CacheDB.Write() failed. Did this CacheDB expire?")
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}
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}
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// We need a copy of all of the keys.
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// Not the best, but probably not a bottleneck depending.
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keys := make([]string, 0, len(db.cache))
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for key, dbValue := range db.cache {
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if dbValue.dirty {
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keys = append(keys, key)
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}
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}
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sort.Strings(keys)
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batch := db.parent.NewBatch()
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for _, key := range keys {
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dbValue := db.cache[key]
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if dbValue.deleted {
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batch.Delete([]byte(key))
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} else if dbValue.value == nil {
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// Skip, it already doesn't exist in parent.
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} else {
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batch.Set([]byte(key), dbValue.value)
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}
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}
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batch.Write()
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// Clear the cache
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db.cache = make(map[string]cDBValue)
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}
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//----------------------------------------
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// To CacheWrap this CacheDB further.
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func (db *CacheDB) CacheWrap() interface{} {
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return NewCacheDB(db, db.GetWriteLockVersion())
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}
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// If the parent parent DB implements this, (e.g. such as a CacheDB parent to a
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// CacheDB child), CacheDB will call `parent.TryWriteLock()` before attempting
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// to write.
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type WriteLocker interface {
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GetWriteLockVersion() (lockVersion interface{})
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TryWriteLock(lockVersion interface{}) bool
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}
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// Implements TryWriteLocker. Embed this in DB structs if desired.
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type cwwMutex struct {
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mtx sync.Mutex
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// CONTRACT: reading/writing to `*written` should use `atomic.*`.
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// CONTRACT: replacing `written` with another *int32 should use `.mtx`.
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written *int32
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}
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func NewCWWMutex() cwwMutex {
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return cwwMutex{
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written: new(int32),
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}
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}
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func (cww *cwwMutex) GetWriteLockVersion() interface{} {
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cww.mtx.Lock()
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defer cww.mtx.Unlock()
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// `written` works as a "version" object because it gets replaced upon
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// successful TryWriteLock.
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return cww.written
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}
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func (cww *cwwMutex) TryWriteLock(version interface{}) bool {
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cww.mtx.Lock()
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defer cww.mtx.Unlock()
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if version != cww.written {
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return false // wrong "WriteLockVersion"
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}
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if !atomic.CompareAndSwapInt32(cww.written, 0, 1) {
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return false // already written
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}
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// New "WriteLockVersion"
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cww.written = new(int32)
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return true
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}
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