@@ -87,17 +87,14 @@ type Iterator interface {
8787 ComputeStats (start , end MVCCKey , nowNanos int64 ) (MVCCStats , error )
8888}
8989
90- // Engine is the interface that wraps the core operations of a
91- // key/value store.
92- type Engine interface {
93- // Open initializes the engine.
94- Open () error
95- // Close closes the engine, freeing up any outstanding resources.
90+ // Reader is the read interface to an engine's data.
91+ type Reader interface {
92+ // Close closes the reader, freeing up any outstanding resources.
9693 Close ()
97- // Attrs returns the engine/store attributes .
98- Attrs () roachpb. Attributes
99- // Put sets the given key to the value provided .
100- Put ( key MVCCKey , value [] byte ) error
94+ // closed returns true if the reader has been closed or is not usable .
95+ // Objects backed by this reader (e.g. Iterators) can check this to ensure
96+ // that they are not using a closed engine .
97+ closed () bool
10198 // Get returns the value for the given key, nil otherwise.
10299 Get (key MVCCKey ) ([]byte , error )
103100 // GetProto fetches the value at the specified key and unmarshals it
@@ -111,6 +108,21 @@ type Engine interface {
111108 // an error, the iteration will stop and return the error.
112109 // If the first result of f is true, the iteration stops.
113110 Iterate (start , end MVCCKey , f func (MVCCKeyValue ) (bool , error )) error
111+ // NewIterator returns a new instance of an Iterator over this engine. When
112+ // prefix is true, Seek will use the user-key prefix of the supplied MVCC key
113+ // to restrict which sstables are searched, but iteration (using Next) over
114+ // keys without the same user-key prefix will not work correctly (keys may be
115+ // skipped). The caller must invoke Iterator.Close() when finished with the
116+ // iterator to free resources.
117+ NewIterator (prefix bool ) Iterator
118+ }
119+
120+ // Writer is the write interface to an engine's data.
121+ type Writer interface {
122+ // ApplyBatchRepr atomically applies a set of batched updates. Created by
123+ // calling Repr() on a batch. Using this method is equivalent to constructing
124+ // and committing a batch whose Repr() equals repr.
125+ ApplyBatchRepr (repr []byte ) error
114126 // Clear removes the item from the db with the given key.
115127 // Note that clear actually removes entries from the storage
116128 // engine, rather than inserting tombstones.
@@ -129,67 +141,63 @@ type Engine interface {
129141 //
130142 // The logic for merges is written in db.cc in order to be compatible with RocksDB.
131143 Merge (key MVCCKey , value []byte ) error
144+ // Put sets the given key to the value provided.
145+ Put (key MVCCKey , value []byte ) error
146+ }
147+
148+ // ReadWriter is the read/write interface to an engine's data.
149+ type ReadWriter interface {
150+ Reader
151+ Writer
152+ }
153+
154+ // Engine is the interface that wraps the core operations of a key/value store.
155+ type Engine interface {
156+ ReadWriter
157+ // Attrs returns the engine/store attributes.
158+ Attrs () roachpb.Attributes
132159 // Capacity returns capacity details for the engine's available storage.
133160 Capacity () (roachpb.StoreCapacity , error )
134161 // Flush causes the engine to write all in-memory data to disk
135162 // immediately.
136163 Flush () error
137- // NewIterator returns a new instance of an Iterator over this engine. When
138- // prefix is true, Seek will use the user-key prefix of the supplied MVCC key
139- // to restrict which sstables are searched, but iteration (using Next) over
140- // keys without the same user-key prefix will not work correctly (keys may be
141- // skipped). The caller must invoke Iterator.Close() when finished with the
142- // iterator to free resources.
143- NewIterator (prefix bool ) Iterator
164+ // GetStats retrieves stats from the engine.
165+ GetStats () (* Stats , error )
166+ // NewBatch returns a new instance of a batched engine which wraps
167+ // this engine. Batched engines accumulate all mutations and apply
168+ // them atomically on a call to Commit().
169+ NewBatch () Batch
144170 // NewSnapshot returns a new instance of a read-only snapshot
145171 // engine. Snapshots are instantaneous and, as long as they're
146172 // released relatively quickly, inexpensive. Snapshots are released
147173 // by invoking Close(). Note that snapshots must not be used after the
148174 // original engine has been stopped.
149- NewSnapshot () Engine
150- // NewBatch returns a new instance of a batched engine which wraps
151- // this engine. Batched engines accumulate all mutations and apply
152- // them atomically on a call to Commit().
153- NewBatch () Batch
154- // Commit atomically applies any batched updates to the underlying
155- // engine. This is a noop unless the engine was created via NewBatch().
156- Commit () error
157- // ApplyBatchRepr atomically applies a set of batched updates. Created by
158- // calling Repr() on a batch. Using this method is equivalent to constructing
159- // and committing a batch whose Repr() equals repr.
160- ApplyBatchRepr (repr []byte ) error
161- // Repr returns the underlying representation of the batch and can be used to
162- // reconstitute the batch on a remote node using
163- // Engine.NewBatchFromRepr(). This method is only valid on engines created
164- // via NewBatch().
165- Repr () []byte
166- // Defer adds a callback to be run after the batch commits
167- // successfully. If Commit() fails (or if this engine was not
168- // created via NewBatch()), deferred callbacks are not called. As
169- // with the defer statement, the last callback to be deferred is the
170- // first to be executed.
171- Defer (fn func ())
172- // Closed returns true if the engine has been close or not usable.
173- // Objects backed by this engine (e.g. Iterators) can check this to ensure
174- // that they are not using an closed engine.
175- Closed () bool
176- // GetStats retrieves stats from the engine.
177- GetStats () (* Stats , error )
175+ NewSnapshot () Reader
176+ // Open initializes the engine.
177+ Open () error
178178}
179179
180180// Batch is the interface for batch specific operations.
181- //
182- // TODO(peter): Move various methods of Engine to Batch, such as Commit() and Repr().
183181type Batch interface {
184- Engine
182+ ReadWriter
183+ // Commit atomically applies any batched updates to the underlying
184+ // engine. This is a noop unless the engine was created via NewBatch().
185+ Commit () error
186+ // Defer adds a callback to be run after the batch commits successfully. If
187+ // Commit() fails deferred callbacks are not called. As with the defer
188+ // statement, the last callback to be deferred is the first to be executed.
189+ Defer (fn func ())
185190 // Distinct returns a view of the existing batch which passes reads directly
186191 // to the underlying engine (the one the batch was created from). That is,
187192 // the returned batch will not read its own writes. This is used as an
188193 // optimization to avoid flushing mutations buffered by the batch in
189194 // situations where we know all of the batched operations are for distinct
190195 // keys. Closing/committing the returned engine is equivalent to
191196 // closing/committing the original batch.
192- Distinct () Engine
197+ Distinct () ReadWriter
198+ // Repr returns the underlying representation of the batch and can be used to
199+ // reconstitute the batch on a remote node using Writer.ApplyBatchRepr().
200+ Repr () []byte
193201}
194202
195203// Stats is a set of RocksDB stats. These are all described in RocksDB
@@ -220,7 +228,7 @@ type Stats struct {
220228// PutProto sets the given key to the protobuf-serialized byte string
221229// of msg and the provided timestamp. Returns the length in bytes of
222230// key and the value.
223- func PutProto (engine Engine , key MVCCKey , msg proto.Message ) (keyBytes , valBytes int64 , err error ) {
231+ func PutProto (engine Writer , key MVCCKey , msg proto.Message ) (keyBytes , valBytes int64 , err error ) {
224232 bytes , err := protoutil .Marshal (msg )
225233 if err != nil {
226234 return 0 , 0 , err
@@ -236,7 +244,7 @@ func PutProto(engine Engine, key MVCCKey, msg proto.Message) (keyBytes, valBytes
236244// Scan returns up to max key/value objects starting from
237245// start (inclusive) and ending at end (non-inclusive).
238246// Specify max=0 for unbounded scans.
239- func Scan (engine Engine , start , end MVCCKey , max int64 ) ([]MVCCKeyValue , error ) {
247+ func Scan (engine Reader , start , end MVCCKey , max int64 ) ([]MVCCKeyValue , error ) {
240248 var kvs []MVCCKeyValue
241249 err := engine .Iterate (start , end , func (kv MVCCKeyValue ) (bool , error ) {
242250 if max != 0 && int64 (len (kvs )) >= max {
@@ -254,18 +262,16 @@ func Scan(engine Engine, start, end MVCCKey, max int64) ([]MVCCKeyValue, error)
254262// none, and an error will be returned. Note that this function
255263// actually removes entries from the storage engine, rather than
256264// inserting tombstones, as with deletion through the MVCC.
257- func ClearRange (engine Engine , start , end MVCCKey ) (int , error ) {
258- b := engine .NewBatch ()
259- defer b .Close ()
265+ func ClearRange (engine ReadWriter , start , end MVCCKey ) (int , error ) {
260266 count := 0
261267 if err := engine .Iterate (start , end , func (kv MVCCKeyValue ) (bool , error ) {
262- if err := b .Clear (kv .Key ); err != nil {
268+ if err := engine .Clear (kv .Key ); err != nil {
263269 return false , err
264270 }
265271 count ++
266272 return false , nil
267273 }); err != nil {
268274 return 0 , err
269275 }
270- return count , b . Commit ()
276+ return count , nil
271277}
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