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Diffstat (limited to 'db/dur_journalformat.h')
| -rw-r--r-- | db/dur_journalformat.h | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/db/dur_journalformat.h b/db/dur_journalformat.h new file mode 100644 index 0000000..d29f94d --- /dev/null +++ b/db/dur_journalformat.h @@ -0,0 +1,166 @@ +// @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 +* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +* 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 <http://www.gnu.org/licenses/>. +*/ + +#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() + + } + +} |