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 (
+        "time"
+
+        ds "github.com/luci/gae/service/datastore"
+        "github.com/luci/gae/service/memcache"
+        log "github.com/luci/luci-go/common/logging"
+        "golang.org/x/net/context"
+)
+
+type dsCache struct {
+        ds.RawInterface
+
+        *supportContext
+}
+
+var _ ds.RawInterface = (*dsCache)(nil)
+
+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)
+        })
+}
+
+func (d *dsCache) GetMulti(keys []ds.Key, metas ds.MultiMetaGetter, cb ds.GetMultiCB) error {
+        lockItems, nonce := d.mkRandLockItems(keys, metas)
+        if len(lockItems) == 0 {
+                return d.RawInterface.GetMulti(keys, metas, cb)
+        }
+
+        if err := d.mc.AddMulti(lockItems); err != nil {
+                (log.Fields{log.ErrorKey: err}).Warningf(
+                        d.c, "dscache: GetMulti: memcache.AddMulti")
+
+        }
+        if err := d.mc.GetMulti(lockItems); err != nil {
+                (log.Fields{log.ErrorKey: err}).Warningf(
+                        d.c, "dscache: GetMulti: memcache.GetMulti")
+        }
+
+        p := makeFetchPlan(d.c, d.aid, d.ns, &facts{keys, metas, lockItems, nonce})
+
+        if !p.empty() {
+                // looks like we have something to pull from datastore, and maybe some work
+                // to save stuff back to memcache.
+
+                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]
+                        j++
+
+                        data := []byte(nil)
+
+                        // true: save entity to memcache
+                        // false: lock entity in memcache forever
+                        shouldSave := true
+                        if err == nil {
+                                p.decoded[i] = pm
+                                if toSave != nil {
+                                        data = encodeItemValue(pm)
+                                        if len(data) > internalValueSizeLimit {
+                                                shouldSave = false
+                                                log.Warningf(
+                                                        d.c, "dscache: encoded entity too big (%d/%d)!",
+                                                        len(data), internalValueSizeLimit)
+                                        }
+                                }
+                        } else {
+                                p.lme.Assign(i, err)
+                                if err != ds.ErrNoSuchEntity {
+                                        return // aka continue to the next entry
+                                }
+                        }
+
+                        if toSave != nil {
+                                if shouldSave { // save
+                                        expSecs := metas.GetMetaDefault(i, CacheExpirationMeta, CacheTimeSeconds).(int64)
+                                        toSave.SetFlags(uint32(ItemHasData))
+                                        toSave.SetExpiration(time.Duration(expSecs) * time.Second)
+                                        toSave.SetValue(data)
+                                } else {
+                                        // Set a lock with an infinite timeout. No one else should try to
+                                        // serialize this item to memcache until something Put/Delete's it.
+                                        toSave.SetFlags(uint32(ItemHasLock))
+                                        toSave.SetExpiration(0)
+                                        toSave.SetValue(nil)
+                                }
+                                toCas = append(toCas, toSave)
+                        }
+                })
+                if err != nil {
+                        return err
+                }
+                if len(toCas) > 0 {
+                        // we have entries to save back to memcache.
+                        if err := d.mc.CompareAndSwapMulti(toCas); err != nil {
+                                (log.Fields{log.ErrorKey: err}).Warningf(
+                                        d.c, "dscache: GetMulti: memcache.CompareAndSwapMulti")
+                        }
+                }
+        }
+
+        // finally, run the callback for all of the decoded items and the errors,
+        // if any.
+        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 {
+                        err = txnState.apply(d.supportContext)
+                }
+                return err
+        }, opts)
+        if err == nil {
+                txnState.release(d.supportContext)
+        }
+        return err
+}