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memdb.go
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memdb.go
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package memdb
import (
"context"
"errors"
"fmt"
"math"
"sort"
"sync"
"time"
"github.com/google/uuid"
"github.com/hashicorp/go-memdb"
"github.com/shopspring/decimal"
"github.com/authzed/spicedb/pkg/datastore"
"github.com/authzed/spicedb/pkg/datastore/revision"
corev1 "github.com/authzed/spicedb/pkg/proto/core/v1"
)
const (
defaultWatchBufferLength = 128
numRetries = 10
)
var errSerialization = errors.New("serialization error")
// DisableGC is a convenient constant for setting the garbage collection
// interval high enough that it will never run.
const DisableGC = time.Duration(math.MaxInt64)
// NewMemdbDatastore creates a new Datastore compliant datastore backed by memdb.
//
// If the watchBufferLength value of 0 is set then a default value of 128 will be used.
func NewMemdbDatastore(
watchBufferLength uint16,
revisionQuantization,
gcWindow time.Duration,
) (datastore.Datastore, error) {
if revisionQuantization > gcWindow {
return nil, errors.New("gc window must be larger than quantization interval")
}
if revisionQuantization <= 1 {
revisionQuantization = 1
}
db, err := memdb.NewMemDB(schema)
if err != nil {
return nil, err
}
if watchBufferLength == 0 {
watchBufferLength = defaultWatchBufferLength
}
uniqueID := uuid.NewString()
negativeGCWindow := decimal.NewFromInt(gcWindow.Nanoseconds()).Mul(decimal.NewFromInt(-1))
return &memdbDatastore{
db: db,
revisions: []snapshot{
{
revision: revisionFromTimestamp(time.Now().UTC()).Decimal,
db: db,
},
},
negativeGCWindow: negativeGCWindow,
quantizationPeriod: decimal.NewFromInt(revisionQuantization.Nanoseconds()),
watchBufferLength: watchBufferLength,
uniqueID: uniqueID,
}, nil
}
type memdbDatastore struct {
sync.RWMutex
revision.DecimalDecoder
db *memdb.MemDB
revisions []snapshot
activeWriteTxn *memdb.Txn
negativeGCWindow decimal.Decimal
quantizationPeriod decimal.Decimal
watchBufferLength uint16
uniqueID string
}
type snapshot struct {
revision decimal.Decimal
db *memdb.MemDB
}
func (mdb *memdbDatastore) SnapshotReader(revisionRaw datastore.Revision) datastore.Reader {
dr := revisionRaw.(revision.Decimal)
mdb.RLock()
defer mdb.RUnlock()
if len(mdb.revisions) == 0 {
return &memdbReader{nil, nil, fmt.Errorf("memdb datastore is not ready")}
}
if err := mdb.checkRevisionLocalCallerMustLock(dr); err != nil {
return &memdbReader{nil, nil, err}
}
revIndex := sort.Search(len(mdb.revisions), func(i int) bool {
return mdb.revisions[i].revision.GreaterThanOrEqual(dr.Decimal)
})
// handle the case when there is no revision snapshot newer than the requested revision
if revIndex == len(mdb.revisions) {
revIndex = len(mdb.revisions) - 1
}
rev := mdb.revisions[revIndex]
if rev.db == nil {
return &memdbReader{nil, nil, fmt.Errorf("memdb datastore is already closed")}
}
roTxn := rev.db.Txn(false)
txSrc := func() (*memdb.Txn, error) {
return roTxn, nil
}
return &memdbReader{noopTryLocker{}, txSrc, nil}
}
func (mdb *memdbDatastore) ReadWriteTx(
ctx context.Context,
f datastore.TxUserFunc,
) (datastore.Revision, error) {
for i := 0; i < numRetries; i++ {
var tx *memdb.Txn
createTxOnce := sync.Once{}
txSrc := func() (*memdb.Txn, error) {
var err error
createTxOnce.Do(func() {
mdb.Lock()
defer mdb.Unlock()
if mdb.activeWriteTxn != nil {
err = errSerialization
return
}
if mdb.db == nil {
err = fmt.Errorf("datastore is closed")
return
}
tx = mdb.db.Txn(true)
tx.TrackChanges()
mdb.activeWriteTxn = tx
})
return tx, err
}
newRevision := mdb.newRevisionID()
rwt := &memdbReadWriteTx{memdbReader{&sync.Mutex{}, txSrc, nil}, newRevision}
if err := f(rwt); err != nil {
mdb.Lock()
if tx != nil {
tx.Abort()
mdb.activeWriteTxn = nil
}
// If the error was a serialization error, retry the transaction
if errors.Is(err, errSerialization) {
mdb.Unlock()
// If we don't sleep here, we run out of retries instantaneously
time.Sleep(1 * time.Millisecond)
continue
}
defer mdb.Unlock()
// We *must* return the inner error unmodified in case it's not an error type
// that supports unwrapping (e.g. gRPC errors)
return datastore.NoRevision, err
}
mdb.Lock()
defer mdb.Unlock()
// Record the changes that were made
newChanges := datastore.RevisionChanges{
Revision: newRevision,
Changes: nil,
}
if tx != nil {
for _, change := range tx.Changes() {
if change.Table == tableRelationship {
if change.After != nil {
rt, err := change.After.(*relationship).RelationTuple()
if err != nil {
return datastore.NoRevision, err
}
newChanges.Changes = append(newChanges.Changes, &corev1.RelationTupleUpdate{
Operation: corev1.RelationTupleUpdate_TOUCH,
Tuple: rt,
})
}
if change.After == nil && change.Before != nil {
rt, err := change.Before.(*relationship).RelationTuple()
if err != nil {
return datastore.NoRevision, err
}
newChanges.Changes = append(newChanges.Changes, &corev1.RelationTupleUpdate{
Operation: corev1.RelationTupleUpdate_DELETE,
Tuple: rt,
})
}
}
}
change := &changelog{
revisionNanos: newRevision.IntPart(),
changes: newChanges,
}
if err := tx.Insert(tableChangelog, change); err != nil {
return datastore.NoRevision, fmt.Errorf("error writing changelog: %w", err)
}
tx.Commit()
}
mdb.activeWriteTxn = nil
// Create a snapshot and add it to the revisions slice
if mdb.db == nil {
return datastore.NoRevision, fmt.Errorf("datastore has been closed")
}
snap := mdb.db.Snapshot()
mdb.revisions = append(mdb.revisions, snapshot{newRevision.Decimal, snap})
return newRevision, nil
}
return datastore.NoRevision, errors.New("serialization max retries exceeded")
}
func (mdb *memdbDatastore) IsReady(ctx context.Context) (bool, error) {
mdb.RLock()
defer mdb.RUnlock()
return len(mdb.revisions) > 0, nil
}
func (mdb *memdbDatastore) Features(ctx context.Context) (*datastore.Features, error) {
return &datastore.Features{Watch: datastore.Feature{Enabled: true}}, nil
}
func (mdb *memdbDatastore) Close() error {
mdb.Lock()
defer mdb.Unlock()
// TODO Make this nil once we have removed all access to closed datastores
if db := mdb.db; db != nil {
mdb.revisions = []snapshot{
{
revision: revisionFromTimestamp(time.Now().UTC()).Decimal,
db: db,
},
}
} else {
mdb.revisions = []snapshot{}
}
mdb.db = nil
return nil
}
var _ datastore.Datastore = &memdbDatastore{}