Redo Logs

The idb::innodb::log module provides types and functions for reading InnoDB redo log files. These are ib_logfile0/ib_logfile1 for MySQL versions before 8.0.30, or #ib_redo* numbered files for MySQL 8.0.30 and later.

File Layout

An InnoDB redo log file consists of 512-byte blocks:

• Block 0: Log file header (group ID, start LSN, file number, creator string)
• Block 1: Checkpoint slot 0
• Block 2: Reserved
• Block 3: Checkpoint slot 1
• Blocks 4+: Data blocks containing redo log records

Each block has a 14-byte header and a 4-byte trailer (CRC-32C checksum at bytes 508-511).

Opening a Redo Log

From a file path

use idb::innodb::log::LogFile;

let mut log = LogFile::open("/var/lib/mysql/ib_logfile0").unwrap();
println!("File size: {} bytes", log.file_size());
println!("Total blocks: {}", log.block_count());
println!("Data blocks: {}", log.data_block_count());

LogFile::open is not available on wasm32 targets.

From an in-memory buffer

use idb::innodb::log::LogFile;

let data: Vec<u8> = std::fs::read("/var/lib/mysql/ib_logfile0").unwrap();
let mut log = LogFile::from_bytes(data).unwrap();

The file must be at least 2048 bytes (4 blocks of 512 bytes for the header and checkpoint areas).

Reading the File Header

use idb::innodb::log::LogFile;

let mut log = LogFile::open("/var/lib/mysql/ib_logfile0").unwrap();
let header = log.read_header().unwrap();

println!("Group ID: {}", header.group_id);
println!("Start LSN: {}", header.start_lsn);
println!("File number: {}", header.file_no);
println!("Created by: {}", header.created_by);

LogFileHeader Fields

The created_by string can be used for vendor detection:

use idb::innodb::log::LogFile;
use idb::innodb::vendor::detect_vendor_from_created_by;

let mut log = LogFile::open("/var/lib/mysql/ib_logfile0").unwrap();
let header = log.read_header().unwrap();
let vendor = detect_vendor_from_created_by(&header.created_by);
println!("Vendor: {}", vendor);

Reading Checkpoints

InnoDB maintains two checkpoint slots for crash recovery. Slot 0 is in block 1, slot 1 is in block 3.

use idb::innodb::log::LogFile;

let mut log = LogFile::open("/var/lib/mysql/ib_logfile0").unwrap();

let cp0 = log.read_checkpoint(0).unwrap();
println!("Checkpoint 0: number={}, LSN={}, offset={}, buf_size={}",
    cp0.number, cp0.lsn, cp0.offset, cp0.buf_size);

let cp1 = log.read_checkpoint(1).unwrap();
println!("Checkpoint 1: number={}, LSN={}, offset={}, buf_size={}",
    cp1.number, cp1.lsn, cp1.offset, cp1.buf_size);

LogCheckpoint Fields

Reading Data Blocks

use idb::innodb::log::{LogFile, LogBlockHeader, LogBlockTrailer, LOG_FILE_HDR_BLOCKS};

let mut log = LogFile::open("/var/lib/mysql/ib_logfile0").unwrap();

// Read data blocks (starting at block 4, after header/checkpoint blocks)
for block_no in LOG_FILE_HDR_BLOCKS..log.block_count() {
    let block = log.read_block(block_no).unwrap();
    let header = LogBlockHeader::parse(&block).unwrap();

    if header.has_data() {
        println!("Block {}: data_len={}, flush={}, checkpoint_no={}",
            header.block_no, header.data_len, header.flush_flag, header.checkpoint_no);
    }
}

LogBlockHeader Fields

The has_data() method returns true when data_len exceeds the header size (14 bytes), indicating the block contains log record data.

Block Checksum Validation

Each 512-byte block has a CRC-32C checksum stored in the last 4 bytes (offset 508-511), covering bytes 0-507.

use idb::innodb::log::{LogFile, validate_log_block_checksum, LOG_FILE_HDR_BLOCKS};

let mut log = LogFile::open("/var/lib/mysql/ib_logfile0").unwrap();

for block_no in LOG_FILE_HDR_BLOCKS..log.block_count() {
    let block = log.read_block(block_no).unwrap();
    let valid = validate_log_block_checksum(&block);
    if !valid {
        println!("Block {} has invalid checksum", block_no);
    }
}

MLOG Record Types

The MlogRecordType enum classifies redo log record types from MySQL's mtr0types.h. This is useful for analyzing what operations are recorded in the redo log.

use idb::innodb::log::MlogRecordType;

let rec_type = MlogRecordType::from_u8(9);
println!("{}", rec_type);        // "MLOG_REC_INSERT"
println!("{}", rec_type.name()); // "MLOG_REC_INSERT"

let unknown = MlogRecordType::from_u8(200);
println!("{}", unknown);         // "UNKNOWN(200)"

Common MLOG Record Types

Unknown type codes are represented as MlogRecordType::Unknown(value).

Block Count Methods

Constants

The module exports several constants matching MySQL's log0log.h: