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kvstore.go
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kvstore.go
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// Copyright (c) 2014 Couchbase, Inc.
// 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 store
import "encoding/json"
// KVStore is an abstraction for working with KV stores
type KVStore interface {
// Writer returns a KVWriter which can be used to
// make changes to the KVStore. If a writer cannot
// be obtained a non-nil error is returned.
Writer() (KVWriter, error)
// Reader returns a KVReader which can be used to
// read data from the KVStore. If a reader cannot
// be obtained a non-nil error is returned.
Reader() (KVReader, error)
// Close closes the KVStore
Close() error
}
// KVReader is an abstraction of an **ISOLATED** reader
// In this context isolated is defined to mean that
// writes/deletes made after the KVReader is opened
// are not observed.
// Because there is usually a cost associated with
// keeping isolated readers active, users should
// close them as soon as they are no longer needed.
type KVReader interface {
// Get returns the value associated with the key
// If the key does not exist, nil is returned.
// The caller owns the bytes returned.
Get(key []byte) ([]byte, error)
// MultiGet retrieves multiple values in one call.
MultiGet(keys [][]byte) ([][]byte, error)
// PrefixIterator returns a KVIterator that will
// visit all K/V pairs with the provided prefix
PrefixIterator(prefix []byte) KVIterator
// RangeIterator returns a KVIterator that will
// visit all K/V pairs >= start AND < end
RangeIterator(start, end []byte) KVIterator
// Close closes the iterator
Close() error
}
// KVIterator is an abstraction around key iteration
type KVIterator interface {
// Seek will advance the iterator to the specified key
Seek(key []byte)
// Next will advance the iterator to the next key
Next()
// Key returns the key pointed to by the iterator
// The bytes returned are **ONLY** valid until the next call to Seek/Next/Close
// Continued use after that requires that they be copied.
Key() []byte
// Value returns the value pointed to by the iterator
// The bytes returned are **ONLY** valid until the next call to Seek/Next/Close
// Continued use after that requires that they be copied.
Value() []byte
// Valid returns whether or not the iterator is in a valid state
Valid() bool
// Current returns Key(),Value(),Valid() in a single operation
Current() ([]byte, []byte, bool)
// Close closes the iterator
Close() error
}
// KVWriter is an abstraction for mutating the KVStore
// KVWriter does **NOT** enforce restrictions of a single writer
// if the underlying KVStore allows concurrent writes, the
// KVWriter interface should also do so, it is up to the caller
// to do this in a way that is safe and makes sense
type KVWriter interface {
// NewBatch returns a KVBatch for performing batch operations on this kvstore
NewBatch() KVBatch
// NewBatchEx returns a KVBatch and an associated byte array
// that's pre-sized based on the KVBatchOptions. The caller can
// use the returned byte array for keys and values associated with
// the batch. Once the batch is either executed or closed, the
// associated byte array should no longer be accessed by the
// caller.
NewBatchEx(KVBatchOptions) ([]byte, KVBatch, error)
// ExecuteBatch will execute the KVBatch, the provided KVBatch **MUST** have
// been created by the same KVStore (though not necessarily the same KVWriter)
// Batch execution is atomic, either all the operations or none will be performed
ExecuteBatch(batch KVBatch) error
// Close closes the writer
Close() error
}
// KVBatchOptions provides the KVWriter.NewBatchEx() method with batch
// preparation and preallocation information.
type KVBatchOptions struct {
// TotalBytes is the sum of key and value bytes needed by the
// caller for the entire batch. It affects the size of the
// returned byte array of KVWrite.NewBatchEx().
TotalBytes int
// NumSets is the number of Set() calls the caller will invoke on
// the KVBatch.
NumSets int
// NumMerges is the number of Merge() calls the caller will invoke
// on the KVBatch.
NumDeletes int
// NumMerges is the number of Merge() calls the caller will invoke
// on the KVBatch.
NumMerges int
}
// KVBatch is an abstraction for making multiple KV mutations at once
type KVBatch interface {
// Set updates the key with the specified value
// both key and value []byte may be reused as soon as this call returns
Set(key, val []byte)
// Delete removes the specified key
// the key []byte may be reused as soon as this call returns
Delete(key []byte)
// Merge merges old value with the new value at the specified key
// as prescribed by the KVStores merge operator
// both key and value []byte may be reused as soon as this call returns
Merge(key, val []byte)
// Reset frees resources for this batch and allows reuse
Reset()
// Close frees resources
Close() error
}
// KVStoreStats is an optional interface that KVStores can implement
// if they're able to report any useful stats
type KVStoreStats interface {
// Stats returns a JSON serializable object representing stats for this KVStore
Stats() json.Marshaler
StatsMap() map[string]interface{}
}