Struct LogBlockHeader 

pub struct LogBlockHeader {
    pub block_no: u32,
    pub flush_flag: bool,
    pub data_len: u16,
    pub first_rec_group: u16,
    pub epoch_no: u32,
}

Log block header (first 12 bytes of each 512-byte block).

The block header layout is consistent across MySQL versions:

Offset	Size	Field
0	4	Block number (bit 31 = flush flag)
4	2	Data length (including header bytes)
6	2	First record group offset
8	4	Epoch number (called checkpoint_no in older versions)

In MySQL < 8.0.30, the header was 14 bytes with 2 extra bytes at offset 12-13 that were part of the checkpoint number. In 8.0.30+ the header is 12 bytes and offset 8 stores the epoch number.

Fields

block_no: u32

Block number (with flush bit masked out).

flush_flag: bool

Whether this block was the first in a flush batch (bit 31).

data_len: u16

Number of bytes of log data in this block (including header).

first_rec_group: u16

Offset of the first log record group starting in this block.

epoch_no: u32

Epoch number (MySQL 8.0.30+) or checkpoint number (older versions).

In MySQL 8.0.30+ and 9.x, this field stores the epoch number used for log block validation. In older versions, it was the checkpoint sequence number.

Implementations

impl LogBlockHeader

pub fn parse(block: &[u8]) -> Option<Self>

Parse a log block header from a 512-byte block.

Examples

use idb::innodb::log::{LogBlockHeader, LOG_BLOCK_HDR_SIZE};
use byteorder::{BigEndian, ByteOrder};

let mut block = vec![0u8; LOG_BLOCK_HDR_SIZE];
BigEndian::write_u32(&mut block[0..], 0x80000005); // flush bit + block_no=5
BigEndian::write_u16(&mut block[4..], 200);        // data_len
BigEndian::write_u16(&mut block[6..], 14);         // first_rec_group
BigEndian::write_u32(&mut block[8..], 3);          // epoch_no

let hdr = LogBlockHeader::parse(&block).unwrap();
assert_eq!(hdr.block_no, 5);
assert!(hdr.flush_flag);
assert_eq!(hdr.data_len, 200);
assert_eq!(hdr.first_rec_group, 14);
assert_eq!(hdr.epoch_no, 3);
assert!(hdr.has_data());

pub fn checkpoint_no(&self) -> u32

Backward-compatible accessor: returns epoch_no as the checkpoint number.

In MySQL < 8.0.30, offset 8 stored the checkpoint number. In 8.0.30+ it stores the epoch number. This accessor preserves API compatibility.

pub fn has_data(&self) -> bool

Returns true if this block contains log data (data_len > header size).

Trait Implementations

impl Clone for LogBlockHeader

fn clone(&self) -> LogBlockHeader

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for LogBlockHeader

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Serialize for LogBlockHeader

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.