github.com/hasnat/dolt/go@v0.0.0-20210628190320-9eb5d843fbb7/store/nbs/manifest_cache.go (about) 1 // Copyright 2019 Dolthub, Inc. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 // This file incorporates work covered by the following copyright and 16 // permission notice: 17 // 18 // Copyright 2016 Attic Labs, Inc. All rights reserved. 19 // Licensed under the Apache License, version 2.0: 20 // http://www.apache.org/licenses/LICENSE-2.0 21 22 package nbs 23 24 import ( 25 "container/list" 26 "fmt" 27 "time" 28 29 "sync" 30 ) 31 32 func newManifestCache(maxSize uint64) *manifestCache { 33 return &manifestCache{ 34 maxSize: maxSize, 35 cache: map[string]manifestCacheEntry{}, 36 mu: &sync.Mutex{}, 37 } 38 } 39 40 type manifestCacheEntry struct { 41 lruEntry *list.Element 42 contents manifestContents 43 t time.Time 44 } 45 46 type manifestCache struct { 47 totalSize uint64 48 maxSize uint64 49 mu *sync.Mutex 50 lru list.List 51 cache map[string]manifestCacheEntry 52 } 53 54 // Get() checks the searches the cache for an entry. If it exists, it moves it's 55 // lru entry to the back of the queue and returns (value, true). Otherwise, it 56 // returns (nil, false). 57 func (mc *manifestCache) Get(db string) (contents manifestContents, t time.Time, present bool) { 58 mc.mu.Lock() 59 defer mc.mu.Unlock() 60 61 if entry, ok := mc.entry(db); ok { 62 contents, t, present = entry.contents, entry.t, true 63 } 64 return 65 } 66 67 // entry() checks if the value is in the cache. If not in the cache, it returns an 68 // empty manifestCacheEntry and false. It it is in the cache, it moves it to 69 // to the back of lru and returns the entry and true. 70 func (mc *manifestCache) entry(key string) (manifestCacheEntry, bool) { 71 entry, ok := mc.cache[key] 72 if !ok { 73 return manifestCacheEntry{}, false 74 } 75 mc.lru.MoveToBack(entry.lruEntry) 76 return entry, true 77 } 78 79 // Put inserts |contents| into the cache with the key |db|, replacing any 80 // currently cached value. Put() will add this element to the cache at the 81 // back of the queue as long it's size does not exceed maxSize. If the 82 // addition of this entry causes the size of the cache to exceed maxSize, the 83 // necessary entries at the front of the queue will be deleted in order to 84 // keep the total cache size below maxSize. |t| must be *prior* to initiating 85 // the call which read/wrote |contents|. 86 func (mc *manifestCache) Put(db string, contents manifestContents, t time.Time) error { 87 mc.mu.Lock() 88 defer mc.mu.Unlock() 89 90 if entry, ok := mc.entry(db); ok { 91 mc.totalSize -= entry.contents.size() 92 mc.lru.Remove(entry.lruEntry) 93 delete(mc.cache, db) 94 } 95 96 if contents.size() <= mc.maxSize { 97 newEl := mc.lru.PushBack(db) 98 ce := manifestCacheEntry{lruEntry: newEl, contents: contents, t: t} 99 mc.cache[db] = ce 100 mc.totalSize += ce.contents.size() 101 for el := mc.lru.Front(); el != nil && mc.totalSize > mc.maxSize; { 102 key1 := el.Value.(string) 103 ce, ok := mc.cache[key1] 104 if !ok { 105 return fmt.Errorf("manifestCache is missing expected value for %s", key1) 106 } 107 next := el.Next() 108 delete(mc.cache, key1) 109 mc.totalSize -= ce.contents.size() 110 mc.lru.Remove(el) 111 el = next 112 } 113 } 114 115 return nil 116 }