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// @file dur_journalformat.h The format of our journal files.
* Copyright (C) 2010 10gen Inc.
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU Affero General Public License for more details.
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <>.
#pragma once
#include "../util/md5.hpp"
namespace mongo {
namespace dur {
#pragma pack(1)
/** beginning header for a journal/j._<n> file
there is nothing important int this header at this time. except perhaps version #.
struct JHeader {
JHeader() { }
JHeader(string fname);
char magic[2]; // "j\n". j means journal, then a linefeed, fwiw if you were to run "less" on the file or something...
// x4142 is asci--readable if you look at the file with head/less -- thus the starting values were near
// that. simply incrementing the version # is safe on a fwd basis.
enum { CurrentVersion = 0x4147 };
unsigned short _version;
// these are just for diagnostic ease (make header more useful as plain text)
char n1; // '\n'
char ts[20]; // ascii timestamp of file generation. for user reading, not used by code.
char n2; // '\n'
char dbpath[128]; // path/filename of this file for human reading and diagnostics. not used by code.
char n3, n4; // '\n', '\n'
unsigned long long fileId; // unique identifier that will be in each JSectHeader. important as we recycle prealloced files
char reserved3[8026]; // 8KB total for the file header
char txt2[2]; // "\n\n" at the end
bool versionOk() const { return _version == CurrentVersion; }
bool valid() const { return magic[0] == 'j' && txt2[1] == '\n' && fileId; }
/** "Section" header. A section corresponds to a group commit.
len is length of the entire section including header and footer.
struct JSectHeader {
unsigned len; // length in bytes of the whole section
unsigned long long seqNumber; // sequence number that can be used on recovery to not do too much work
unsigned long long fileId; // matches JHeader::fileId
/** an individual write operation within a group commit section. Either the entire section should
be applied, or nothing. (We check the md5 for the whole section before doing anything on recovery.)
struct JEntry {
enum OpCodes {
OpCode_Footer = 0xffffffff,
OpCode_DbContext = 0xfffffffe,
OpCode_FileCreated = 0xfffffffd,
OpCode_DropDb = 0xfffffffc,
OpCode_Min = 0xfffff000
union {
unsigned len; // length in bytes of the data of the JEntry. does not include the JEntry header
OpCodes opcode;
unsigned ofs; // offset in file
// sentinel and masks for _fileNo
enum {
DotNsSuffix = 0x7fffffff, // ".ns" file
LocalDbBit = 0x80000000 // assuming "local" db instead of using the JDbContext
int _fileNo; // high bit is set to indicate it should be the <dbpath>/local database
// char data[len] follows
const char * srcData() const {
const int *i = &_fileNo;
return (const char *) (i+1);
int getFileNo() const { return _fileNo & (~LocalDbBit); }
void setFileNo(int f) { _fileNo = f; }
bool isNsSuffix() const { return getFileNo() == DotNsSuffix; }
void setLocalDbContextBit() { _fileNo |= LocalDbBit; }
bool isLocalDbContext() const { return _fileNo & LocalDbBit; }
void clearLocalDbContextBit() { _fileNo = getFileNo(); }
static string suffix(int fileno) {
if( fileno == DotNsSuffix ) return "ns";
stringstream ss;
ss << fileno;
return ss.str();
/** group commit section footer. md5 is a key field. */
struct JSectFooter {
JSectFooter(const void* begin, int len) { // needs buffer to compute hash
sentinel = JEntry::OpCode_Footer;
reserved = 0;
magic[0] = magic[1] = magic[2] = magic[3] = '\n';
// skip section header since size modified after hashing
(const char*&)begin += sizeof(JSectHeader);
len -= sizeof(JSectHeader);
md5(begin, len, hash);
unsigned sentinel;
md5digest hash; // unsigned char[16]
unsigned long long reserved;
char magic[4]; // "\n\n\n\n"
bool checkHash(const void* begin, int len) const {
// skip section header since size modified after hashing
(const char*&)begin += sizeof(JSectHeader);
len -= sizeof(JSectHeader);
md5digest current;
md5(begin, len, current);
DEV log() << "checkHash len:" << len << " hash:" << toHex(hash, 16) << " current:" << toHex(current, 16) << endl;
return (memcmp(hash, current, sizeof(hash)) == 0);
/** declares "the next entry(s) are for this database / file path prefix" */
struct JDbContext {
JDbContext() : sentinel(JEntry::OpCode_DbContext) { }
const unsigned sentinel; // compare to JEntry::len -- zero is our sentinel
//char dbname[];
/** "last sequence number" */
struct LSNFile {
unsigned ver;
unsigned reserved2;
unsigned long long lsn;
unsigned long long checkbytes;
unsigned long long reserved[8];
void set(unsigned long long lsn);
unsigned long long get();
#pragma pack()
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