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entry_cache.go
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entry_cache.go
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// Copyright 2016 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License. See the AUTHORS file
// for names of contributors.
//
// Author: Spencer Kimball (spencer@cockroachlabs.com)
package storage
import (
"github.com/biogo/store/llrb"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/util/cache"
"github.com/cockroachdb/cockroach/pkg/util/syncutil"
"github.com/coreos/etcd/raft/raftpb"
)
type entryCacheKey struct {
RangeID roachpb.RangeID
Index uint64
}
// Compare implements the llrb.Comparable interface for entryCacheKey, so that
// it can be used as a key for util.OrderedCache.
func (a *entryCacheKey) Compare(b llrb.Comparable) int {
bk := b.(*entryCacheKey)
switch {
case a.RangeID < bk.RangeID:
return -1
case a.RangeID > bk.RangeID:
return 1
case a.Index < bk.Index:
return -1
case a.Index > bk.Index:
return 1
default:
return 0
}
}
// A raftEntryCache maintains a global cache of Raft group log
// entries. The cache mostly prevents unnecessary reads from disk of
// recently-written log entries between log append and application
// to the FSM.
type raftEntryCache struct {
syncutil.Mutex // protects Cache for concurrent access.
bytes uint64 // total size of the cache in bytes
cache *cache.OrderedCache // LRU cache of log entries, keyed by rangeID / log index
}
// newRaftEntryCache returns a new RaftEntryCache with the given
// maximum size in bytes.
func newRaftEntryCache(maxBytes uint64) *raftEntryCache {
rec := &raftEntryCache{
cache: cache.NewOrderedCache(cache.Config{Policy: cache.CacheLRU}),
}
// The raft entry cache mutex will be held when the ShouldEvict
// and OnEvicted callbacks are invoked.
//
// On ShouldEvict, compare the total size of the cache in bytes to the
// configured maxBytes. We also insist that at least one entry remains
// in the cache to prevent the case where a very large entry isn't able
// to be cached at all.
rec.cache.Config.ShouldEvict = func(n int, k, v interface{}) bool {
return rec.bytes > maxBytes && n >= 1
}
rec.cache.Config.OnEvicted = func(k, v interface{}) {
ent := v.(*raftpb.Entry)
rec.bytes -= uint64(ent.Size())
}
return rec
}
func (rec *raftEntryCache) makeCacheEntry(key entryCacheKey, value raftpb.Entry) *cache.Entry {
alloc := struct {
key entryCacheKey
value raftpb.Entry
entry cache.Entry
}{
key: key,
value: value,
}
alloc.entry.Key = &alloc.key
alloc.entry.Value = &alloc.value
return &alloc.entry
}
// addEntries adds the slice of raft entries, using the range ID and the
// entry indexes as each cached entry's key.
func (rec *raftEntryCache) addEntries(rangeID roachpb.RangeID, ents []raftpb.Entry) {
if len(ents) == 0 {
return
}
rec.Lock()
defer rec.Unlock()
for _, e := range ents {
rec.bytes += uint64(e.Size())
entry := rec.makeCacheEntry(entryCacheKey{RangeID: rangeID, Index: e.Index}, e)
rec.cache.AddEntry(entry)
}
}
// getEntries returns entries between [lo, hi) for specified range.
// If any entries are returned for the specified indexes, they will
// start with index lo and proceed sequentially without gaps until
// 1) all entries exclusive of hi are fetched, 2) > maxBytes of
// entries data is fetched, or 3) a cache miss occurs.
func (rec *raftEntryCache) getEntries(
ents []raftpb.Entry, rangeID roachpb.RangeID, lo, hi, maxBytes uint64,
) ([]raftpb.Entry, uint64, uint64) {
rec.Lock()
defer rec.Unlock()
var bytes uint64
nextIndex := lo
fromKey := &entryCacheKey{RangeID: rangeID, Index: lo}
toKey := &entryCacheKey{RangeID: rangeID, Index: hi}
rec.cache.DoRange(func(k, v interface{}) bool {
ecKey := k.(*entryCacheKey)
if ecKey.Index != nextIndex {
return true
}
ent := v.(*raftpb.Entry)
ents = append(ents, *ent)
bytes += uint64(ent.Size())
nextIndex++
if maxBytes > 0 && bytes > maxBytes {
return true
}
return false
}, fromKey, toKey)
return ents, bytes, nextIndex
}
// delEntries deletes entries between [lo, hi) for specified range.
func (rec *raftEntryCache) delEntries(rangeID roachpb.RangeID, lo, hi uint64) {
rec.Lock()
defer rec.Unlock()
if lo >= hi {
return
}
var keys []*entryCacheKey
fromKey := &entryCacheKey{RangeID: rangeID, Index: lo}
toKey := &entryCacheKey{RangeID: rangeID, Index: hi}
rec.cache.DoRange(func(k, v interface{}) bool {
keys = append(keys, k.(*entryCacheKey))
return false
}, fromKey, toKey)
for _, k := range keys {
rec.cache.Del(k)
}
}
// clearTo clears the entries in the cache for specified range up to,
// but not including the specified index.
func (rec *raftEntryCache) clearTo(rangeID roachpb.RangeID, index uint64) {
rec.delEntries(rangeID, 0, index)
}