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Handle backwards-compatibility of TimelineMetadata.

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This commit bumps TimelineMetadata format version and makes it independent from STORAGE_FORMAT_VERSION.
This commit is contained in:
Anastasia Lubennikova
2022-09-14 18:34:30 +03:00
parent e2dec100ff
commit a2df9d650e
2 changed files with 148 additions and 19 deletions
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6
pageserver/src/lib.rs
View File

@@ -31,9 +31,11 @@ use crate::task_mgr::TaskKind;
/// Current storage format version
///
/// This is embedded in the metadata file, and also in the header of all the
/// layer files. If you make any backwards-incompatible changes to the storage
/// This is embedded in the header of all the layer files.
/// If you make any backwards-incompatible changes to the storage
/// format, bump this!
/// Note that TimelineMetadata uses its own version number to track
/// backwards-compatible changes to the metadata format.
pub const STORAGE_FORMAT_VERSION: u16 = 3;
pub const DEFAULT_PG_VERSION: u32 = 14;

161
pageserver/src/tenant/metadata.rs
View File

@@ -20,7 +20,12 @@ use utils::{
use crate::config::PageServerConf;
use crate::virtual_file::VirtualFile;
use crate::STORAGE_FORMAT_VERSION;
/// Use special format number to enable backward compatibility.
const METADATA_FORMAT_VERSION: u16 = 4;
/// Previous supported format versions.
const METADATA_OLD_FORMAT_VERSION: u16 = 3;
/// We assume that a write of up to METADATA_MAX_SIZE bytes is atomic.
///
@@ -34,19 +39,19 @@ const METADATA_MAX_SIZE: usize = 512;
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TimelineMetadata {
hdr: TimelineMetadataHeader,
body: TimelineMetadataBody,
body: TimelineMetadataBodyV2,
}
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
struct TimelineMetadataHeader {
checksum: u32, // CRC of serialized metadata body
size: u16, // size of serialized metadata
format_version: u16, // storage format version (used for compatibility checks)
format_version: u16, // metadata format version (used for compatibility checks)
}
const METADATA_HDR_SIZE: usize = std::mem::size_of::<TimelineMetadataHeader>();
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
struct TimelineMetadataBody {
struct TimelineMetadataBodyV2 {
disk_consistent_lsn: Lsn,
// This is only set if we know it. We track it in memory when the page
// server is running, but we only track the value corresponding to
@@ -66,6 +71,26 @@ struct TimelineMetadataBody {
pg_version: u32,
}
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
struct TimelineMetadataBodyV1 {
disk_consistent_lsn: Lsn,
// This is only set if we know it. We track it in memory when the page
// server is running, but we only track the value corresponding to
// 'last_record_lsn', not 'disk_consistent_lsn' which can lag behind by a
// lot. We only store it in the metadata file when we flush *all* the
// in-memory data so that 'last_record_lsn' is the same as
// 'disk_consistent_lsn'. That's OK, because after page server restart, as
// soon as we reprocess at least one record, we will have a valid
// 'prev_record_lsn' value in memory again. This is only really needed when
// doing a clean shutdown, so that there is no more WAL beyond
// 'disk_consistent_lsn'
prev_record_lsn: Option<Lsn>,
ancestor_timeline: Option<TimelineId>,
ancestor_lsn: Lsn,
latest_gc_cutoff_lsn: Lsn,
initdb_lsn: Lsn,
}
impl TimelineMetadata {
pub fn new(
disk_consistent_lsn: Lsn,
@@ -80,9 +105,9 @@ impl TimelineMetadata {
hdr: TimelineMetadataHeader {
checksum: 0,
size: 0,
format_version: STORAGE_FORMAT_VERSION,
format_version: METADATA_FORMAT_VERSION,
},
body: TimelineMetadataBody {
body: TimelineMetadataBodyV2 {
disk_consistent_lsn,
prev_record_lsn,
ancestor_timeline,
@@ -94,16 +119,43 @@ impl TimelineMetadata {
}
}
fn upgrade_timeline_metadata(metadata_bytes: &[u8]) -> anyhow::Result<Self> {
let mut hdr = TimelineMetadataHeader::des(&metadata_bytes[0..METADATA_HDR_SIZE])?;
// backward compatible only up to this version
ensure!(
hdr.format_version == METADATA_OLD_FORMAT_VERSION,
"unsupported metadata format version {}",
hdr.format_version
);
let metadata_size = hdr.size as usize;
let body: TimelineMetadataBodyV1 =
TimelineMetadataBodyV1::des(&metadata_bytes[METADATA_HDR_SIZE..metadata_size])?;
let body = TimelineMetadataBodyV2 {
disk_consistent_lsn: body.disk_consistent_lsn,
prev_record_lsn: body.prev_record_lsn,
ancestor_timeline: body.ancestor_timeline,
ancestor_lsn: body.ancestor_lsn,
latest_gc_cutoff_lsn: body.latest_gc_cutoff_lsn,
initdb_lsn: body.initdb_lsn,
pg_version: 14, // All timelines created before this version had pg_version 14
};
hdr.format_version = METADATA_FORMAT_VERSION;
Ok(Self { hdr, body })
}
pub fn from_bytes(metadata_bytes: &[u8]) -> anyhow::Result<Self> {
ensure!(
metadata_bytes.len() == METADATA_MAX_SIZE,
"metadata bytes size is wrong"
);
let hdr = TimelineMetadataHeader::des(&metadata_bytes[0..METADATA_HDR_SIZE])?;
ensure!(
hdr.format_version == STORAGE_FORMAT_VERSION,
"format version mismatch"
);
let metadata_size = hdr.size as usize;
ensure!(
metadata_size <= METADATA_MAX_SIZE,
@@ -114,13 +166,20 @@ impl TimelineMetadata {
hdr.checksum == calculated_checksum,
"metadata checksum mismatch"
);
let body = TimelineMetadataBody::des(&metadata_bytes[METADATA_HDR_SIZE..metadata_size])?;
ensure!(
body.disk_consistent_lsn.is_aligned(),
"disk_consistent_lsn is not aligned"
);
Ok(TimelineMetadata { hdr, body })
if hdr.format_version != METADATA_FORMAT_VERSION {
// If metadata has the old format,
// upgrade it and return the result
TimelineMetadata::upgrade_timeline_metadata(&metadata_bytes)
} else {
let body =
TimelineMetadataBodyV2::des(&metadata_bytes[METADATA_HDR_SIZE..metadata_size])?;
ensure!(
body.disk_consistent_lsn.is_aligned(),
"disk_consistent_lsn is not aligned"
);
Ok(TimelineMetadata { hdr, body })
}
}
pub fn to_bytes(&self) -> anyhow::Result<Vec<u8>> {
@@ -128,7 +187,7 @@ impl TimelineMetadata {
let metadata_size = METADATA_HDR_SIZE + body_bytes.len();
let hdr = TimelineMetadataHeader {
size: metadata_size as u16,
format_version: STORAGE_FORMAT_VERSION,
format_version: METADATA_FORMAT_VERSION,
checksum: crc32c::crc32c(&body_bytes),
};
let hdr_bytes = hdr.ser()?;
@@ -235,4 +294,72 @@ mod tests {
"Metadata that was serialized to bytes and deserialized back should not change"
);
}
// Generate old version metadata and read it with current code.
// Ensure that it is upgraded correctly
#[test]
fn test_metadata_upgrade() {
#[derive(Debug, Clone, PartialEq, Eq)]
struct TimelineMetadataV1 {
hdr: TimelineMetadataHeader,
body: TimelineMetadataBodyV1,
}
let metadata_v1 = TimelineMetadataV1 {
hdr: TimelineMetadataHeader {
checksum: 0,
size: 0,
format_version: METADATA_OLD_FORMAT_VERSION,
},
body: TimelineMetadataBodyV1 {
disk_consistent_lsn: Lsn(0x200),
prev_record_lsn: Some(Lsn(0x100)),
ancestor_timeline: Some(TIMELINE_ID),
ancestor_lsn: Lsn(0),
latest_gc_cutoff_lsn: Lsn(0),
initdb_lsn: Lsn(0),
},
};
impl TimelineMetadataV1 {
pub fn to_bytes(&self) -> anyhow::Result<Vec<u8>> {
let body_bytes = self.body.ser()?;
let metadata_size = METADATA_HDR_SIZE + body_bytes.len();
let hdr = TimelineMetadataHeader {
size: metadata_size as u16,
format_version: METADATA_OLD_FORMAT_VERSION,
checksum: crc32c::crc32c(&body_bytes),
};
let hdr_bytes = hdr.ser()?;
let mut metadata_bytes = vec![0u8; METADATA_MAX_SIZE];
metadata_bytes[0..METADATA_HDR_SIZE].copy_from_slice(&hdr_bytes);
metadata_bytes[METADATA_HDR_SIZE..metadata_size].copy_from_slice(&body_bytes);
Ok(metadata_bytes)
}
}
let metadata_bytes = metadata_v1
.to_bytes()
.expect("Should serialize correct metadata to bytes");
// This should deserialize to the latest version format
let deserialized_metadata = TimelineMetadata::from_bytes(&metadata_bytes)
.expect("Should deserialize its own bytes");
let expected_metadata = TimelineMetadata::new(
Lsn(0x200),
Some(Lsn(0x100)),
Some(TIMELINE_ID),
Lsn(0),
Lsn(0),
Lsn(0),
14, // All timelines created before this version had pg_version 14
);
assert_eq!(
deserialized_metadata.body, expected_metadata.body,
"Metadata of the old version {} should be upgraded to the latest version {}",
METADATA_OLD_FORMAT_VERSION, METADATA_FORMAT_VERSION
);
}
}