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Avoid discarding transaction too early in queries #31

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Sep 13, 2018
Merged

Avoid discarding transaction too early in queries #31

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36 changes: 26 additions & 10 deletions datastore.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,10 @@ type Datastore struct {
// the badger Datastore.
type txn struct {
txn *badger.Txn

// Whether this transaction has been implicitly created as a result of a direct Datastore
// method invocation.
implicit bool
}

// Options are the badger datastore options, reexported here for convenience.
Expand Down Expand Up @@ -79,11 +83,17 @@ func NewDatastore(path string, options *Options) (*Datastore, error) {
// can be mutated without incurring changes to the underlying Datastore until
// the transaction is Committed.
func (d *Datastore) NewTransaction(readOnly bool) ds.Txn {
return &txn{d.DB.NewTransaction(!readOnly)}
return &txn{d.DB.NewTransaction(!readOnly), false}
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now that we have more than one value in the struct, let's address them by name

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Oops, I merged before addressing this. Worth opening another PR?

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maybe just leave a todo for yourself! i think it's fine.

}

// newImplicitTransaction creates a transaction marked as 'implicit'.
// Implicit transactions are created by Datastore methods performing single operations.
func (d *Datastore) newImplicitTransaction(readOnly bool) ds.Txn {
return &txn{d.DB.NewTransaction(!readOnly), true}
}

func (d *Datastore) Put(key ds.Key, value []byte) error {
txn := d.NewTransaction(false)
txn := d.newImplicitTransaction(false)
defer txn.Discard()

if err := txn.Put(key, value); err != nil {
Expand All @@ -94,7 +104,7 @@ func (d *Datastore) Put(key ds.Key, value []byte) error {
}

func (d *Datastore) PutWithTTL(key ds.Key, value []byte, ttl time.Duration) error {
txn := d.NewTransaction(false).(*txn)
txn := d.newImplicitTransaction(false).(*txn)
defer txn.Discard()

if err := txn.PutWithTTL(key, value, ttl); err != nil {
Expand All @@ -105,7 +115,7 @@ func (d *Datastore) PutWithTTL(key ds.Key, value []byte, ttl time.Duration) erro
}

func (d *Datastore) SetTTL(key ds.Key, ttl time.Duration) error {
txn := d.NewTransaction(false).(*txn)
txn := d.newImplicitTransaction(false).(*txn)
defer txn.Discard()

if err := txn.SetTTL(key, ttl); err != nil {
Expand All @@ -116,21 +126,21 @@ func (d *Datastore) SetTTL(key ds.Key, ttl time.Duration) error {
}

func (d *Datastore) Get(key ds.Key) (value []byte, err error) {
txn := d.NewTransaction(true)
txn := d.newImplicitTransaction(true)
defer txn.Discard()

return txn.Get(key)
}

func (d *Datastore) Has(key ds.Key) (bool, error) {
txn := d.NewTransaction(true)
txn := d.newImplicitTransaction(true)
defer txn.Discard()

return txn.Has(key)
}

func (d *Datastore) Delete(key ds.Key) error {
txn := d.NewTransaction(false)
txn := d.newImplicitTransaction(false)
defer txn.Discard()

err := txn.Delete(key)
Expand All @@ -142,9 +152,10 @@ func (d *Datastore) Delete(key ds.Key) error {
}

func (d *Datastore) Query(q dsq.Query) (dsq.Results, error) {
txn := d.NewTransaction(true)
defer txn.Discard()
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This defer is problematic with badger master, as it discards the txn while the iterator is active.

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This is the error this PR solves:

panic: Unclosed iterator at time of Txn.Discard. [recovered]
	panic: Unclosed iterator at time of Txn.Discard.


txn := d.newImplicitTransaction(true)
// We cannot defer txn.Discard() here, as the txn must remain active while the iterator is open.
// https://github.com/dgraph-io/badger/commit/b1ad1e93e483bbfef123793ceedc9a7e34b09f79
// The closing logic in the query goprocess takes care of discarding the implicit transaction.
return txn.Query(q)
}

Expand Down Expand Up @@ -243,6 +254,11 @@ func (t *txn) Query(q dsq.Query) (dsq.Results, error) {
qrb := dsq.NewResultBuilder(q)

qrb.Process.Go(func(worker goprocess.Process) {
if t.implicit {
// this iterator is part of an implicit transaction, so when we're done we must discard
// the transaction. It's safe to discard the txn it because it contains the iterator only.
defer t.Discard()
}
defer it.Close()

for sent := 0; it.ValidForPrefix(prefix); sent++ {
Expand Down