Implement Transactions: Part 2

- Move all errors into a new file: errors.go.
- Remove all public APIs from kv.go. All the public APIs now flow through transactions.
- Remove SetIfAbsent, CompareAndSet, etc. They should all be done via transactions now.
- Remove CAS counter from everywhere.
- Simplify serialization/deserialization of various structs.
- Move them into new structs.go file (currently only contains value.go structs).
- Logic to handle transaction boundaries when replaying value log.

errors.go

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2017 Dgraph Labs, Inc. and Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package badger
+
+import (
+	"encoding/hex"
+
+	"github.com/pkg/errors"
+)
+
+// ErrInvalidDir is returned when Badger cannot find the directory
+// from where it is supposed to load the key-value store.
+var ErrInvalidDir = errors.New("Invalid Dir, directory does not exist")
+
+// ErrValueLogSize is returned when opt.ValueLogFileSize option is not within the valid
+// range.
+var ErrValueLogSize = errors.New("Invalid ValueLogFileSize, must be between 1MB and 2GB")
+
+// ErrKeyNotFound is returned when key isn't found on a txn.Get.
+var ErrKeyNotFound = errors.New("Key not found")
+
+// ErrTxnTooBig is returned if too many writes are fit into a single transaction.
+var ErrTxnTooBig = errors.New("Txn is too big to fit into one request.")
+
+// ErrConflict is returned when a transaction conflicts with another transaction. This can happen if
+// the read rows had been updated concurrently by another transaction.
+var ErrConflict = errors.New("Transaction Conflict. Please retry.")
+
+// ErrReadOnlyTxn is returned if an update function is called on a read-only transaction.
+var ErrReadOnlyTxn = errors.New("No sets or deletes are allowed in a read-only transaction.")
+
+// ErrEmptyKey is returned if an empty key is passed on an update function.
+var ErrEmptyKey = errors.New("Key cannot be empty.")
+
+const maxKeySize = 1 << 20
+
+func exceedsMaxKeySizeError(key []byte) error {
+	return errors.Errorf("Key with size %d exceeded %dMB limit. Key:\n%s",
+		len(key), maxKeySize<<20, hex.Dump(key[:1<<10]))
+}
+
+func exceedsMaxValueSizeError(value []byte, maxValueSize int64) error {
+	return errors.Errorf("Value with size %d exceeded ValueLogFileSize (%dMB). Key:\n%s",
+		len(value), maxValueSize<<20, hex.Dump(value[:1<<10]))
+}
+
+var (
+	// ErrRetry is returned when a log file containing the value is not found.
+	// This usually indicates that it may have been garbage collected, and the
+	// operation needs to be retried.
+	ErrRetry = errors.New("Unable to find log file. Please retry")
+
+	// ErrThresholdZero is returned if threshold is set to zero, and value log GC is called.
+	// In such a case, GC can't be run.
+	ErrThresholdZero = errors.New(
+		"Value log GC can't run because threshold is set to zero")
+
+	// ErrNoRewrite is returned if a call for value log GC doesn't result in a log file rewrite.
+	ErrNoRewrite = errors.New(
+		"Value log GC attempt didn't result in any cleanup")
+
+	// ErrRejected is returned if a value log GC is called either while another GC is running, or
+	// after KV::Close has been called.
+	ErrRejected = errors.New("Value log GC request rejected")
+
+	// ErrInvalidRequest is returned if the user request is invalid.
+	ErrInvalidRequest = errors.New("Invalid request")
+)

iterator.go

@@ -34,18 +34,17 @@ const (
 // KVItem is returned during iteration. Both the Key() and Value() output is only valid until
 // iterator.Next() is called.
 type KVItem struct {
-	status     prefetchStatus
-	err        error
-	wg         sync.WaitGroup
-	kv         *KV
-	key        []byte
-	vptr       []byte
-	meta       byte
-	userMeta   byte
-	val        []byte
-	casCounter uint64   // TODO: Rename to version ts.
-	slice      *y.Slice // Used only during prefetching.
-	next       *KVItem
+	status   prefetchStatus
+	err      error
+	wg       sync.WaitGroup
+	kv       *KV
+	key      []byte
+	vptr     []byte
+	meta     byte
+	userMeta byte
+	val      []byte
+	slice    *y.Slice // Used only during prefetching.
+	next     *KVItem
 }
 
 // Key returns the key. Remember to copy if you need to access it outside the iteration loop.
@@ -116,10 +115,9 @@ func (item *KVItem) EstimatedSize() int64 {
 	return int64(vp.Len) // includes key length.
 }
 
-// Counter returns the CAS counter associated with the value.
-// TODO: Make this version.
-func (item *KVItem) Counter() uint64 {
-	return item.casCounter
+// Version returns the commit timestamp of the item.
+func (item *KVItem) Version() uint64 {
+	return y.ParseTs(item.key)
 }
 
 // UserMeta returns the userMeta set by the user. Typically, this byte, optionally set by the user
@@ -322,7 +320,6 @@ func (it *Iterator) fill(item *KVItem) {
 	vs := it.iitr.Value()
 	item.meta = vs.Meta
 	item.userMeta = vs.UserMeta
-	item.casCounter = vs.CASCounter
 	item.key = y.Safecopy(item.key, it.iitr.Key())
 	item.vptr = y.Safecopy(item.vptr, vs.Value)
 	item.val = nil