server: Move server files to 'server' directory.

26  git mv mvcc wal auth etcdserver etcdmain proxy embed/ lease/ server
   36  git mv go.mod go.sum server

server/wal/doc.go

@@ -0,0 +1,75 @@
+// Copyright 2015 The etcd Authors
+//
+// 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 wal provides an implementation of a write ahead log that is used by
+etcd.
+
+A WAL is created at a particular directory and is made up of a number of
+segmented WAL files. Inside of each file the raft state and entries are appended
+to it with the Save method:
+
+	metadata := []byte{}
+	w, err := wal.Create(zap.NewExample(), "/var/lib/etcd", metadata)
+	...
+	err := w.Save(s, ents)
+
+After saving a raft snapshot to disk, SaveSnapshot method should be called to
+record it. So WAL can match with the saved snapshot when restarting.
+
+	err := w.SaveSnapshot(walpb.Snapshot{Index: 10, Term: 2})
+
+When a user has finished using a WAL it must be closed:
+
+	w.Close()
+
+Each WAL file is a stream of WAL records. A WAL record is a length field and a wal record
+protobuf. The record protobuf contains a CRC, a type, and a data payload. The length field is a
+64-bit packed structure holding the length of the remaining logical record data in its lower
+56 bits and its physical padding in the first three bits of the most significant byte. Each
+record is 8-byte aligned so that the length field is never torn. The CRC contains the CRC32
+value of all record protobufs preceding the current record.
+
+WAL files are placed inside of the directory in the following format:
+$seq-$index.wal
+
+The first WAL file to be created will be 0000000000000000-0000000000000000.wal
+indicating an initial sequence of 0 and an initial raft index of 0. The first
+entry written to WAL MUST have raft index 0.
+
+WAL will cut its current tail wal file if its size exceeds 64MB. This will increment an internal
+sequence number and cause a new file to be created. If the last raft index saved
+was 0x20 and this is the first time cut has been called on this WAL then the sequence will
+increment from 0x0 to 0x1. The new file will be: 0000000000000001-0000000000000021.wal.
+If a second cut issues 0x10 entries with incremental index later then the file will be called:
+0000000000000002-0000000000000031.wal.
+
+At a later time a WAL can be opened at a particular snapshot. If there is no
+snapshot, an empty snapshot should be passed in.
+
+	w, err := wal.Open("/var/lib/etcd", walpb.Snapshot{Index: 10, Term: 2})
+	...
+
+The snapshot must have been written to the WAL.
+
+Additional items cannot be Saved to this WAL until all of the items from the given
+snapshot to the end of the WAL are read first:
+
+	metadata, state, ents, err := w.ReadAll()
+
+This will give you the metadata, the last raft.State and the slice of
+raft.Entry items in the log.
+
+*/
+package wal