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Support read-only nodes

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Change 'zenith.signal' file to a human-readable format, similar to
backup_label. It can contain a "PREV LSN: %X/%X" line, or a special
value to indicate that it's OK to start with invalid LSN ('none'), or
that it's a read-only node and generating WAL is forbidden
('invalid').

The 'zenith pg create' and 'zenith pg start' commands now take a node
name parameter, separate from the branch name. If the node name is not
given, it defaults to the branch name, so this doesn't break existing
scripts.

If you pass "foo@<lsn>" as the branch name, a read-only node anchored
at that LSN is created. The anchoring is performed by setting the
'recovery_target_lsn' option in the postgresql.conf file, and putting
the server into standby mode with 'standby.signal'.

We no longer store the synthetic checkpoint record in the WAL segment.
The postgres startup code has been changed to use the copy of the
checkpoint record in the pg_control file, when starting in zenith
mode.
This commit is contained in:
Heikki Linnakangas
2021-10-19 09:48:12 +03:00
parent c2b468c958
commit feae7f39c1
10 changed files with 233 additions and 95 deletions
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45
postgres_ffi/src/xlog_utils.rs
View File

@@ -9,7 +9,6 @@
use crate::pg_constants;
use crate::CheckPoint;
use crate::ControlFileData;
use crate::FullTransactionId;
use crate::XLogLongPageHeaderData;
use crate::XLogPageHeaderData;
@@ -18,8 +17,8 @@ use crate::XLOG_PAGE_MAGIC;
use anyhow::{bail, Result};
use byteorder::{ByteOrder, LittleEndian};
use bytes::BytesMut;
use bytes::{Buf, Bytes};
use bytes::{BufMut, BytesMut};
use crc32c::*;
use log::*;
use std::cmp::max;
@@ -410,27 +409,25 @@ impl CheckPoint {
}
//
// Generate new WAL segment with single XLOG_CHECKPOINT_SHUTDOWN record.
// Generate new, empty WAL segment.
// We need this segment to start compute node.
// In order to minimize changes in Postgres core, we prefer to
// provide WAL segment from which is can extract checkpoint record in standard way,
// rather then implement some alternative mechanism.
//
pub fn generate_wal_segment(pg_control: &ControlFileData) -> Bytes {
pub fn generate_wal_segment(segno: u64, system_id: u64) -> Bytes {
let mut seg_buf = BytesMut::with_capacity(pg_constants::WAL_SEGMENT_SIZE as usize);
let pageaddr = XLogSegNoOffsetToRecPtr(segno, 0, pg_constants::WAL_SEGMENT_SIZE);
let hdr = XLogLongPageHeaderData {
std: {
XLogPageHeaderData {
xlp_magic: XLOG_PAGE_MAGIC as u16,
xlp_info: pg_constants::XLP_LONG_HEADER,
xlp_tli: 1, // FIXME: always use Postgres timeline 1
xlp_pageaddr: pg_control.checkPoint - XLOG_SIZE_OF_XLOG_LONG_PHD as u64,
xlp_pageaddr: pageaddr,
xlp_rem_len: 0,
..Default::default() // Put 0 in padding fields.
}
},
xlp_sysid: pg_control.system_identifier,
xlp_sysid: system_id,
xlp_seg_size: pg_constants::WAL_SEGMENT_SIZE as u32,
xlp_xlog_blcksz: XLOG_BLCKSZ as u32,
};
@@ -438,36 +435,6 @@ pub fn generate_wal_segment(pg_control: &ControlFileData) -> Bytes {
let hdr_bytes = hdr.encode();
seg_buf.extend_from_slice(&hdr_bytes);
let rec_hdr = XLogRecord {
xl_tot_len: (XLOG_SIZE_OF_XLOG_RECORD
+ SIZE_OF_XLOG_RECORD_DATA_HEADER_SHORT
+ SIZEOF_CHECKPOINT) as u32,
xl_xid: 0, //0 is for InvalidTransactionId
xl_prev: 0,
xl_info: pg_constants::XLOG_CHECKPOINT_SHUTDOWN,
xl_rmid: pg_constants::RM_XLOG_ID,
xl_crc: 0,
..Default::default() // Put 0 in padding fields.
};
let mut rec_shord_hdr_bytes = BytesMut::new();
rec_shord_hdr_bytes.put_u8(pg_constants::XLR_BLOCK_ID_DATA_SHORT);
rec_shord_hdr_bytes.put_u8(SIZEOF_CHECKPOINT as u8);
let rec_bytes = rec_hdr.encode();
let checkpoint_bytes = pg_control.checkPointCopy.encode();
//calculate record checksum
let mut crc = 0;
crc = crc32c_append(crc, &rec_shord_hdr_bytes[..]);
crc = crc32c_append(crc, &checkpoint_bytes[..]);
crc = crc32c_append(crc, &rec_bytes[0..XLOG_RECORD_CRC_OFFS]);
seg_buf.extend_from_slice(&rec_bytes[0..XLOG_RECORD_CRC_OFFS]);
seg_buf.put_u32_le(crc);
seg_buf.extend_from_slice(&rec_shord_hdr_bytes);
seg_buf.extend_from_slice(&checkpoint_bytes);
//zero out the rest of the file
seg_buf.resize(pg_constants::WAL_SEGMENT_SIZE, 0);
seg_buf.freeze()