A transparent cache for datastore, backed by memcache.

filter/dscache/ds.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package dscache
+
+import (
+        "bytes"
+        "fmt"
+        "math/rand"
+        "time"
+
+        ds "github.com/luci/gae/service/datastore"
+        "github.com/luci/gae/service/memcache"
+        "github.com/luci/luci-go/common/errors"
+        "github.com/luci/luci-go/common/logging"
+        "golang.org/x/net/context"
+)
+
+type dsCache struct {
+        ds.RawInterface
+
+        aid string
+        ns  string
+
+        mc  memcache.Interface
+        log logging.Logger
+        mr  *rand.Rand
+}
+
+var _ ds.RawInterface = (*dsCache)(nil)
+
+func (d *dsCache) mutation(keys []ds.Key, f func() error) error {
+        lockItems, lockKeys := mkAllLockItems(d.mc, keys)
+        if lockItems == nil {
+                return f()
+        }
+        if err := d.mc.SetMulti(lockItems); err != nil {
+                d.log.Errorf("dscache: mc.SetMulti: %s", err)
+        }
+        err := f()
+        if err == nil {
+                if err := d.mc.DeleteMulti(lockKeys); err != nil {
+                        d.log.Errorf("dscache: mc.DeleteMulti: %s", err)
+                }
+        }
+        return err
+}
+
+func (d *dsCache) DeleteMulti(keys []ds.Key, cb ds.DeleteMultiCB) error {
+        return d.mutation(keys, func() error {
+                return d.RawInterface.DeleteMulti(keys, cb)
+        })
+}
+
+func (d *dsCache) PutMulti(keys []ds.Key, vals []ds.PropertyMap, cb ds.PutMultiCB) error {
+        return d.mutation(keys, func() error {
+                return d.RawInterface.PutMulti(keys, vals, cb)
+        })
+}
+
+type facts struct {
+        getKeys   []ds.Key
+        getMeta   []ds.PropertyMap
+        lockItems []memcache.Item
+}
+
+type plan struct {
+        keepMeta bool
+
+        idxMap    []int
+        toGet     []ds.Key
+        toGetMeta []ds.PropertyMap
+        toSave    []memcache.Item
+
+        decoded []ds.PropertyMap
+        lme     errors.LazyMultiError
+}
+
+func (p *plan) add(idx int, get ds.Key, m ds.PropertyMap, save memcache.Item) {
+        p.idxMap = append(p.idxMap, idx)
+        p.toGet = append(p.toGet, get)
+
+        if save != nil {
+                save.SetFlags(uint32(ItemHasData))
+        }
+        p.toSave = append(p.toSave, save)
+
+        if p.keepMeta {
+                p.toGetMeta = append(p.toGetMeta, m)
+        }
+}
+
+func (p *plan) empty() bool {
+        return len(p.idxMap) == 0
+}
+
+func (d *dsCache) makePlan(f *facts) *plan {
+        // get index -> items index
+        p := plan{
+                keepMeta: f.getMeta != nil,
+                decoded:  make([]ds.PropertyMap, len(f.lockItems)),
+                lme:      errors.LazyMultiError{Size: len(f.lockItems)},
+        }
+        for i, lockItm := range f.lockItems {
+                curItm := f.lockItems[i]
+                m := ds.PropertyMap(nil)
+                if f.getMeta != nil {
+                        m = f.getMeta[i]
+                }
+
+                getKey := f.getKeys[i]
+                if !meta(m, CacheEnableMeta, true).(bool) {
+                        fmt.Println("cache is disabled!")
+                        p.add(i, getKey, m, nil)
+                        continue
+                }
+
+                if curItm == nil {
+                        fmt.Println("missing item in memcache!")
+                        p.add(i, getKey, m, nil)
+                        continue
+                }
+
+                flg := FlagValue(curItm.Flags())
+                if flg == ItemHasLock {
+                        if !bytes.Equal(curItm.Value(), lockItm.Value()) {
+                                curItm = nil // someone else has the lock, don't save
+                        }
+                        fmt.Println("found lock item in memcache!")
+                        p.add(i, getKey, m, curItm)
+                        continue
+                }
+
+                pmap, err := decodeValue(curItm.Value(), d.aid, d.ns)
+                switch err {
+                case nil:
+                        p.decoded[i] = pmap
+                case ds.ErrNoSuchEntity:
+                        p.lme.Assign(i, ds.ErrNoSuchEntity)
+                default:
+                        d.log.Errorf("dscache: error decoding %s, %s: %s", curItm.Key(), getKey, err)
+                        fmt.Println("failed to decode!")
+                        p.add(i, getKey, m, curItm)
+                }
+        }
+        return &p
+}
+
+func (d *dsCache) GetMulti(keys []ds.Key, metas []ds.PropertyMap, cb ds.GetMultiCB) error {
+        lockItems := mkRandLockItems(d.mc, d.mr, keys)
+        if lockItems == nil {
+                return d.RawInterface.GetMulti(keys, metas, cb)
+        }
+
+        if err := d.mc.AddMulti(lockItems); err != nil {
+                d.log.Errorf("dscache: mc.AddMulti: %s", err)
+        }
+        if err := d.mc.GetMulti(lockItems); err != nil {
+                d.log.Errorf("dscache: mc.GetMulti: %s", err)
+        }
+
+        p := d.makePlan(&facts{keys, metas, lockItems})
+
+        if !p.empty() {
+                fmt.Println("have to touch DS :(", p)
+                toCas := []memcache.Item{}
+                j := 0
+                err := d.RawInterface.GetMulti(p.toGet, p.toGetMeta, func(pm ds.PropertyMap, err error) {
+                        i := p.idxMap[j]
+                        toSave := p.toSave[j]
+
+                        data := []byte(nil)
+
+                        if err == nil {
+                                p.decoded[i] = pm
+                                if toSave != nil {
+                                        data, err = mkItemData(pm)
+                                }
+                        }
+
+                        canSave := true
+                        if err != nil {
+                                p.lme.Assign(i, err)
+                                canSave = err == ds.ErrNoSuchEntity
+                        }
+
+                        if canSave && toSave != nil {
+                                m := ds.PropertyMap(nil)
+                                if p.toGetMeta != nil {
+                                        m = p.toGetMeta[j]
+                                }
+                                expSecs := meta(m, CacheExpirationMeta, CacheTimeSeconds).(int64)
+                                toSave.SetExpiration(time.Duration(expSecs) * time.Second)
+                                toSave.SetValue(data)
+                                toCas = append(toCas, toSave)
+                        }
+
+                        j++
+                })
+                if err != nil {
+                        return err
+                }
+                if len(toCas) > 0 {
+                        if err := d.mc.CompareAndSwapMulti(toCas); err != nil {
+                                d.log.Errorf("dscache: CompareAndSwapMulti: %s", err)
+                        }
+                }
+        }
+
+        for i, dec := range p.decoded {
+                cb(dec, p.lme.GetOne(i))
+        }
+
+        return nil
+}
+
+func (d *dsCache) RunInTransaction(f func(context.Context) error, opts *ds.TransactionOptions) error {
+        txnState := dsTxnState{}
+        err := d.RawInterface.RunInTransaction(func(ctx context.Context) error {
+                txnState.Reset()
+                err := f(context.WithValue(ctx, dsTxnCacheKey, &txnState))
+                if err != nil {
+                        txnState.Apply(d.mc, d.log)
+                }
+                return err
+        }, opts)
+        if err == nil {
+                txnState.Release(d.mc, d.log)
+        }
+        return err
+}