1/* 2 * snapshot.go 3 * 4 * This source file is part of the FoundationDB open source project 5 * 6 * Copyright 2013-2018 Apple Inc. and the FoundationDB project authors 7 * 8 * Licensed under the Apache License, Version 2.0 (the "License"); 9 * you may not use this file except in compliance with the License. 10 * You may obtain a copy of the License at 11 * 12 * http://www.apache.org/licenses/LICENSE-2.0 13 * 14 * Unless required by applicable law or agreed to in writing, software 15 * distributed under the License is distributed on an "AS IS" BASIS, 16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 17 * See the License for the specific language governing permissions and 18 * limitations under the License. 19 */ 20 21// FoundationDB Go API 22 23package fdb 24 25// Snapshot is a handle to a FoundationDB transaction snapshot, suitable for 26// performing snapshot reads. Snapshot reads offer a more relaxed isolation 27// level than FoundationDB's default serializable isolation, reducing 28// transaction conflicts but making it harder to reason about concurrency. 29// 30// For more information on snapshot reads, see 31// https://apple.github.io/foundationdb/developer-guide.html#snapshot-reads. 32type Snapshot struct { 33 *transaction 34} 35 36// ReadTransact executes the caller-provided function, passing it the Snapshot 37// receiver object (as a ReadTransaction). 38// 39// A panic of type Error during execution of the function will be recovered and 40// returned to the caller as an error, but ReadTransact will not retry the 41// function. 42// 43// By satisfying the ReadTransactor interface, Snapshot may be passed to a 44// read-only transactional function from another (possibly read-only) 45// transactional function, allowing composition. 46// 47// See the ReadTransactor interface for an example of using ReadTransact with 48// Transaction, Snapshot and Database objects. 49func (s Snapshot) ReadTransact(f func(ReadTransaction) (interface{}, error)) (r interface{}, e error) { 50 defer panicToError(&e) 51 52 r, e = f(s) 53 return 54} 55 56// Snapshot returns the receiver and allows Snapshot to satisfy the 57// ReadTransaction interface. 58func (s Snapshot) Snapshot() Snapshot { 59 return s 60} 61 62// Get is equivalent to (Transaction).Get, performed as a snapshot read. 63func (s Snapshot) Get(key KeyConvertible) FutureByteSlice { 64 return s.get(key.FDBKey(), 1) 65} 66 67// GetKey is equivalent to (Transaction).GetKey, performed as a snapshot read. 68func (s Snapshot) GetKey(sel Selectable) FutureKey { 69 return s.getKey(sel.FDBKeySelector(), 1) 70} 71 72// GetRange is equivalent to (Transaction).GetRange, performed as a snapshot 73// read. 74func (s Snapshot) GetRange(r Range, options RangeOptions) RangeResult { 75 return s.getRange(r, options, true) 76} 77 78// GetReadVersion is equivalent to (Transaction).GetReadVersion, performed as 79// a snapshot read. 80func (s Snapshot) GetReadVersion() FutureInt64 { 81 return s.getReadVersion() 82} 83 84// GetDatabase returns a handle to the database with which this snapshot is 85// interacting. 86func (s Snapshot) GetDatabase() Database { 87 return s.transaction.db 88} 89