122 lines
4.1 KiB
Go
122 lines
4.1 KiB
Go
// Copyright (c) 2014 Couchbase, Inc.
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
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// except in compliance with the License. You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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// Unless required by applicable law or agreed to in writing, software distributed under the
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// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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// either express or implied. See the License for the specific language governing permissions
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// and limitations under the License.
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package store
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// KVStore is an abstraction for working with KV stores
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type KVStore interface {
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// Writer returns a KVWriter which can be used to
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// make changes to the KVStore. If a writer cannot
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// be obtained a non-nil error is returned.
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Writer() (KVWriter, error)
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// Reader returns a KVReader which can be used to
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// read data from the KVStore. If a reader cannot
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// be obtained a non-nil error is returned.
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Reader() (KVReader, error)
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// Close closes the KVStore
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Close() error
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}
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// KVReader is an abstraction of an **ISOLATED** reader
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// In this context isolated is defined to mean that
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// writes/deletes made after the KVReader is opened
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// are not observed.
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// Because there is usually a cost associated with
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// keeping isolated readers active, users should
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// close them as soon as they are no longer needed.
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type KVReader interface {
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// Get returns the value associated with the key
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// If the key does not exist, nil is returned.
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// The caller owns the bytes returned.
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Get(key []byte) ([]byte, error)
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// PrefixIterator returns a KVIterator that will
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// visit all K/V pairs with the provided prefix
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PrefixIterator(prefix []byte) KVIterator
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// RangeIterator returns a KVIterator that will
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// visit all K/V pairs >= start AND < end
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RangeIterator(start, end []byte) KVIterator
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// Close closes the iterator
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Close() error
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}
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// KVIterator is an abstraction around key iteration
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type KVIterator interface {
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// Seek will advance the iterator to the specified key
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Seek(key []byte)
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// Next will advance the iterator to the next key
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Next()
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// Key returns the key pointed to by the iterator
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// The bytes returned are **ONLY** valid until the next call to Seek/Next/Close
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// Continued use after that requires that they be copied.
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Key() []byte
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// Value returns the value pointed to by the iterator
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// The bytes returned are **ONLY** valid until the next call to Seek/Next/Close
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// Continued use after that requires that they be copied.
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Value() []byte
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// Valid returns whether or not the iterator is in a valid state
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Valid() bool
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// Current returns Key(),Value(),Valid() in a single operation
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Current() ([]byte, []byte, bool)
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// Close closes the iterator
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Close() error
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}
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// KVWriter is an abstraction for mutating the KVStore
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// KVWriter does **NOT** enforce restrictions of a single writer
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// if the underlying KVStore allows concurrent writes, the
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// KVWriter interface should also do so, it is up to the caller
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// to do this in a way that is safe and makes sense
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type KVWriter interface {
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// NewBatch returns a KVBatch for performaing batch operations on this kvstore
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NewBatch() KVBatch
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// ExecuteBatch will execute the KVBatch, the provided KVBatch **MUST** have
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// been created by the same KVStore (though not necessarily the same KVWriter)
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// Batch execution is atomic, either all the operations or none will be performed
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ExecuteBatch(batch KVBatch) error
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// Close closes the writer
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Close() error
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}
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// KVBatch is an abstraction for making multiple KV mutations at once
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type KVBatch interface {
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// Set updates the key with the specified value
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// both key and value []byte may be reused as soon as this call returns
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Set(key, val []byte)
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// Delete removes the specified key
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// the key []byte may be reused as soon as this call returns
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Delete(key []byte)
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// Merge merges old value with the new value at the specified key
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// as prescribed by the KVStores merge operator
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// both key and value []byte may be reused as soon as this call returns
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Merge(key, val []byte)
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// Reset frees resources for this batch and allows reuse
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Reset()
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}
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