forked from Deuxfleurs/garage
Refactor model stuff, including cleaner CRDTs
This commit is contained in:
parent
6a3dcf3974
commit
f319a7d374
20 changed files with 591 additions and 457 deletions
|
@ -66,25 +66,28 @@ pub async fn handle_copy(
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.await?;
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let source_version = source_version.ok_or(Error::NotFound)?;
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let dest_version = Version::new(
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let mut dest_version = Version::new(
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new_uuid,
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dest_bucket.to_string(),
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dest_key.to_string(),
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false,
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source_version.blocks().to_vec(),
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);
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for (bk, bv) in source_version.blocks.items().iter() {
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dest_version.blocks.put(*bk, *bv);
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}
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let dest_object = Object::new(
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dest_bucket.to_string(),
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dest_key.to_string(),
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vec![dest_object_version],
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);
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let dest_block_refs = dest_version
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.blocks()
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.blocks
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.items()
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.iter()
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.map(|b| BlockRef {
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block: b.hash,
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block: b.1.hash,
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version: new_uuid,
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deleted: false,
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deleted: false.into(),
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})
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.collect::<Vec<_>>();
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futures::try_join!(
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@ -146,9 +146,10 @@ pub async fn handle_get(
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let version = version.ok_or(Error::NotFound)?;
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let mut blocks = version
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.blocks()
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.blocks
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.items()
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.iter()
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.map(|vb| (vb.hash, None))
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.map(|(_, vb)| (vb.hash, None))
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.collect::<Vec<_>>();
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blocks[0].1 = Some(first_block);
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@ -219,11 +220,12 @@ pub async fn handle_get_range(
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// file (whereas block.offset designates the offset of the block WITHIN THE PART
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// block.part_number, which is not the same in the case of a multipart upload)
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let mut blocks = Vec::with_capacity(std::cmp::min(
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version.blocks().len(),
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4 + ((end - begin) / std::cmp::max(version.blocks()[0].size as u64, 1024)) as usize,
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version.blocks.len(),
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4 + ((end - begin) / std::cmp::max(version.blocks.items()[0].1.size as u64, 1024))
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as usize,
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));
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let mut true_offset = 0;
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for b in version.blocks().iter() {
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for (_, b) in version.blocks.items().iter() {
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if true_offset >= end {
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break;
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}
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@ -94,7 +94,7 @@ pub async fn handle_put(
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garage.object_table.insert(&object).await?;
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// Initialize corresponding entry in version table
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let version = Version::new(version_uuid, bucket.into(), key.into(), false, vec![]);
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let version = Version::new(version_uuid, bucket.into(), key.into(), false);
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let first_block_hash = sha256sum(&first_block[..]);
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// Transfer data and verify checksum
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@ -242,19 +242,18 @@ async fn put_block_meta(
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) -> Result<(), GarageError> {
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// TODO: don't clone, restart from empty block list ??
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let mut version = version.clone();
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version
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.add_block(VersionBlock {
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version.blocks.put(
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VersionBlockKey {
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part_number,
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offset,
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hash,
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size,
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})
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.unwrap();
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},
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VersionBlock { hash, size },
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);
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let block_ref = BlockRef {
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block: hash,
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version: version.uuid,
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deleted: false,
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deleted: false.into(),
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};
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futures::try_join!(
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@ -389,7 +388,7 @@ pub async fn handle_put_part(
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}
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// Copy block to store
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let version = Version::new(version_uuid, bucket, key, false, vec![]);
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let version = Version::new(version_uuid, bucket, key, false);
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let first_block_hash = sha256sum(&first_block[..]);
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let (_, md5sum_arr, sha256sum) = read_and_put_blocks(
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&garage,
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@ -454,7 +453,7 @@ pub async fn handle_complete_multipart_upload(
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};
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let version = version.ok_or(Error::BadRequest(format!("Version not found")))?;
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if version.blocks().len() == 0 {
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if version.blocks.len() == 0 {
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return Err(Error::BadRequest(format!("No data was uploaded")));
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}
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@ -466,9 +465,10 @@ pub async fn handle_complete_multipart_upload(
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// Check that the list of parts they gave us corresponds to the parts we have here
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// TODO: check MD5 sum of all uploaded parts? but that would mean we have to store them somewhere...
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let mut parts = version
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.blocks()
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.blocks
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.items()
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.iter()
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.map(|x| x.part_number)
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.map(|x| x.0.part_number)
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.collect::<Vec<_>>();
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parts.dedup();
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let same_parts = body_list_of_parts
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@ -485,8 +485,8 @@ pub async fn handle_complete_multipart_upload(
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// shouldn't impact compatibility as the S3 docs specify that
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// the ETag is an opaque value in case of a multipart upload.
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// See also: https://teppen.io/2018/06/23/aws_s3_etags/
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let num_parts = version.blocks().last().unwrap().part_number
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- version.blocks().first().unwrap().part_number
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let num_parts = version.blocks.items().last().unwrap().0.part_number
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- version.blocks.items().first().unwrap().0.part_number
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+ 1;
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let etag = format!(
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"{}-{}",
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@ -495,17 +495,18 @@ pub async fn handle_complete_multipart_upload(
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);
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let total_size = version
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.blocks()
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.blocks
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.items()
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.iter()
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.map(|x| x.size)
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.map(|x| x.1.size)
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.fold(0, |x, y| x + y);
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object_version.state = ObjectVersionState::Complete(ObjectVersionData::FirstBlock(
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ObjectVersionMeta {
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headers,
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size: total_size,
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etag: etag,
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etag,
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},
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version.blocks()[0].hash,
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version.blocks.items()[0].1.hash,
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));
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let final_object = Object::new(bucket.clone(), key.clone(), vec![object_version]);
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@ -97,7 +97,7 @@ impl Repair {
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pos = item_key.to_vec();
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let version = rmp_serde::decode::from_read_ref::<_, Version>(item_bytes.as_ref())?;
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if version.deleted {
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if version.deleted.get() {
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continue;
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}
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let object = self
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@ -127,7 +127,6 @@ impl Repair {
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version.bucket,
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version.key,
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true,
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vec![],
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))
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.await?;
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}
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@ -146,7 +145,7 @@ impl Repair {
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pos = item_key.to_vec();
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let block_ref = rmp_serde::decode::from_read_ref::<_, BlockRef>(item_bytes.as_ref())?;
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if block_ref.deleted {
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if block_ref.deleted.get() {
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continue;
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}
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let version = self
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@ -155,7 +154,7 @@ impl Repair {
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.get(&block_ref.version, &EmptyKey)
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.await?;
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let ref_exists = match version {
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Some(v) => !v.deleted,
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Some(v) => !v.deleted.get(),
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None => {
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warn!(
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"Block ref repair: version for block ref {:?} not found, skipping.",
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@ -174,7 +173,7 @@ impl Repair {
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.insert(&BlockRef {
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block: block_ref.block,
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version: block_ref.version,
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deleted: true,
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deleted: true.into(),
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})
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.await?;
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}
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@ -420,7 +420,7 @@ impl BlockManager {
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if Some(&block_ref.block) == last_hash.as_ref() {
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continue;
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}
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if !block_ref.deleted {
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if !block_ref.deleted.get() {
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last_hash = Some(block_ref.block);
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self.put_to_resync(&block_ref.block, 0)?;
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}
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@ -1,9 +1,9 @@
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use serde::{Deserialize, Serialize};
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use std::sync::Arc;
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use garage_util::background::*;
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use garage_util::data::*;
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use garage_table::crdt::CRDT;
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use garage_table::*;
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use crate::block::*;
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@ -17,7 +17,7 @@ pub struct BlockRef {
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pub version: UUID,
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// Keep track of deleted status
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pub deleted: bool,
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pub deleted: crdt::Bool,
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}
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impl Entry<Hash, UUID> for BlockRef {
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@ -27,16 +27,15 @@ impl Entry<Hash, UUID> for BlockRef {
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fn sort_key(&self) -> &UUID {
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&self.version
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}
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fn merge(&mut self, other: &Self) {
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if other.deleted {
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self.deleted = true;
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}
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impl CRDT for BlockRef {
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fn merge(&mut self, other: &Self) {
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self.deleted.merge(&other.deleted);
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}
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}
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pub struct BlockRefTable {
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pub background: Arc<BackgroundRunner>,
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pub block_manager: Arc<BlockManager>,
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}
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@ -48,8 +47,8 @@ impl TableSchema for BlockRefTable {
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fn updated(&self, old: Option<Self::E>, new: Option<Self::E>) {
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let block = &old.as_ref().or(new.as_ref()).unwrap().block;
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let was_before = old.as_ref().map(|x| !x.deleted).unwrap_or(false);
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let is_after = new.as_ref().map(|x| !x.deleted).unwrap_or(false);
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let was_before = old.as_ref().map(|x| !x.deleted.get()).unwrap_or(false);
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let is_after = new.as_ref().map(|x| !x.deleted.get()).unwrap_or(false);
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if is_after && !was_before {
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if let Err(e) = self.block_manager.block_incref(block) {
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warn!("block_incref failed for block {:?}: {}", block, e);
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@ -63,6 +62,6 @@ impl TableSchema for BlockRefTable {
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}
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fn matches_filter(entry: &Self::E, filter: &Self::Filter) -> bool {
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filter.apply(entry.deleted)
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filter.apply(entry.deleted.get())
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}
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}
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@ -89,7 +89,9 @@ impl Entry<EmptyKey, String> for Bucket {
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fn sort_key(&self) -> &String {
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&self.name
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}
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}
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impl CRDT for Bucket {
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fn merge(&mut self, other: &Self) {
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self.state.merge(&other.state);
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}
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@ -79,7 +79,6 @@ impl Garage {
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info!("Initialize block_ref_table...");
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let block_ref_table = Table::new(
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BlockRefTable {
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background: background.clone(),
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block_manager: block_manager.clone(),
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},
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data_rep_param.clone(),
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@ -1,6 +1,6 @@
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use serde::{Deserialize, Serialize};
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use garage_table::crdt::CRDT;
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use garage_table::crdt::*;
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use garage_table::*;
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use model010::key_table as prev;
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@ -66,6 +66,10 @@ pub struct PermissionSet {
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pub allow_write: bool,
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}
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impl AutoCRDT for PermissionSet {
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const WARN_IF_DIFFERENT: bool = true;
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}
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impl Entry<EmptyKey, String> for Key {
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fn partition_key(&self) -> &EmptyKey {
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&EmptyKey
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@ -73,19 +77,20 @@ impl Entry<EmptyKey, String> for Key {
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fn sort_key(&self) -> &String {
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&self.key_id
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}
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}
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impl CRDT for Key {
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fn merge(&mut self, other: &Self) {
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self.name.merge(&other.name);
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self.deleted.merge(&other.deleted);
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if self.deleted.get() {
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self.authorized_buckets.clear();
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return;
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}
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} else {
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self.authorized_buckets.merge(&other.authorized_buckets);
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}
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}
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}
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pub struct KeyTable;
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|
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@ -5,6 +5,7 @@ use std::sync::Arc;
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use garage_util::background::BackgroundRunner;
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use garage_util::data::*;
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use garage_table::crdt::*;
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use garage_table::table_sharded::*;
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use garage_table::*;
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@ -70,7 +71,7 @@ pub enum ObjectVersionState {
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Aborted,
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}
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impl ObjectVersionState {
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impl CRDT for ObjectVersionState {
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fn merge(&mut self, other: &Self) {
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use ObjectVersionState::*;
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match other {
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@ -91,37 +92,30 @@ impl ObjectVersionState {
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}
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}
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#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
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#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
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pub enum ObjectVersionData {
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DeleteMarker,
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Inline(ObjectVersionMeta, #[serde(with = "serde_bytes")] Vec<u8>),
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FirstBlock(ObjectVersionMeta, Hash),
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}
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#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
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impl AutoCRDT for ObjectVersionData {
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const WARN_IF_DIFFERENT: bool = true;
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}
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#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
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pub struct ObjectVersionMeta {
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pub headers: ObjectVersionHeaders,
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pub size: u64,
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pub etag: String,
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}
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#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
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#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
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pub struct ObjectVersionHeaders {
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pub content_type: String,
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pub other: BTreeMap<String, String>,
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}
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impl ObjectVersionData {
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fn merge(&mut self, b: &Self) {
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if *self != *b {
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warn!(
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"Inconsistent object version data: {:?} (local) vs {:?} (remote)",
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self, b
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);
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}
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}
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}
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impl ObjectVersion {
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fn cmp_key(&self) -> (u64, UUID) {
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(self.timestamp, self.uuid)
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|
@ -154,8 +148,11 @@ impl Entry<String, String> for Object {
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fn sort_key(&self) -> &String {
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&self.key
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}
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}
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impl CRDT for Object {
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fn merge(&mut self, other: &Self) {
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// Merge versions from other into here
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for other_v in other.versions.iter() {
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match self
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.versions
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|
@ -169,6 +166,9 @@ impl Entry<String, String> for Object {
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}
|
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}
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}
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// Remove versions which are obsolete, i.e. those that come
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// before the last version which .is_complete().
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let last_complete = self
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.versions
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.iter()
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|
@ -212,13 +212,8 @@ impl TableSchema for ObjectTable {
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}
|
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};
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if newly_deleted {
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let deleted_version = Version::new(
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v.uuid,
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old_v.bucket.clone(),
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old_v.key.clone(),
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true,
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vec![],
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);
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let deleted_version =
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Version::new(v.uuid, old_v.bucket.clone(), old_v.key.clone(), true);
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version_table.insert(&deleted_version).await?;
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}
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}
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|
|
|
@ -4,6 +4,7 @@ use std::sync::Arc;
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use garage_util::background::BackgroundRunner;
|
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use garage_util::data::*;
|
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|
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use garage_table::crdt::*;
|
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use garage_table::table_sharded::*;
|
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use garage_table::*;
|
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|
@ -15,8 +16,8 @@ pub struct Version {
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pub uuid: UUID,
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|
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// Actual data: the blocks for this version
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pub deleted: bool,
|
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blocks: Vec<VersionBlock>,
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pub deleted: crdt::Bool,
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pub blocks: crdt::Map<VersionBlockKey, VersionBlock>,
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|
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// Back link to bucket+key so that we can figure if
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// this was deleted later on
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|
@ -25,56 +26,45 @@ pub struct Version {
|
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}
|
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|
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impl Version {
|
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pub fn new(
|
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uuid: UUID,
|
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bucket: String,
|
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key: String,
|
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deleted: bool,
|
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blocks: Vec<VersionBlock>,
|
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) -> Self {
|
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let mut ret = Self {
|
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pub fn new(uuid: UUID, bucket: String, key: String, deleted: bool) -> Self {
|
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Self {
|
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uuid,
|
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deleted,
|
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blocks: vec![],
|
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deleted: deleted.into(),
|
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blocks: crdt::Map::new(),
|
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bucket,
|
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key,
|
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};
|
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for b in blocks {
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ret.add_block(b)
|
||||
.expect("Twice the same VersionBlock in Version constructor");
|
||||
}
|
||||
ret
|
||||
}
|
||||
/// Adds a block if it wasn't already present
|
||||
pub fn add_block(&mut self, new: VersionBlock) -> Result<(), ()> {
|
||||
match self
|
||||
.blocks
|
||||
.binary_search_by(|b| b.cmp_key().cmp(&new.cmp_key()))
|
||||
{
|
||||
Err(i) => {
|
||||
self.blocks.insert(i, new);
|
||||
Ok(())
|
||||
}
|
||||
Ok(_) => Err(()),
|
||||
}
|
||||
}
|
||||
pub fn blocks(&self) -> &[VersionBlock] {
|
||||
&self.blocks[..]
|
||||
}
|
||||
}
|
||||
|
||||
#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
|
||||
pub struct VersionBlock {
|
||||
#[derive(PartialEq, Eq, Clone, Copy, Debug, Serialize, Deserialize)]
|
||||
pub struct VersionBlockKey {
|
||||
pub part_number: u64,
|
||||
pub offset: u64,
|
||||
}
|
||||
|
||||
impl Ord for VersionBlockKey {
|
||||
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
|
||||
self.part_number
|
||||
.cmp(&other.part_number)
|
||||
.then(self.offset.cmp(&other.offset))
|
||||
}
|
||||
}
|
||||
|
||||
impl PartialOrd for VersionBlockKey {
|
||||
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
|
||||
Some(self.cmp(other))
|
||||
}
|
||||
}
|
||||
|
||||
#[derive(PartialEq, Eq, Ord, PartialOrd, Clone, Copy, Debug, Serialize, Deserialize)]
|
||||
pub struct VersionBlock {
|
||||
pub hash: Hash,
|
||||
pub size: u64,
|
||||
}
|
||||
|
||||
impl VersionBlock {
|
||||
fn cmp_key(&self) -> (u64, u64) {
|
||||
(self.part_number, self.offset)
|
||||
}
|
||||
impl AutoCRDT for VersionBlock {
|
||||
const WARN_IF_DIFFERENT: bool = true;
|
||||
}
|
||||
|
||||
impl Entry<Hash, EmptyKey> for Version {
|
||||
|
@ -84,23 +74,16 @@ impl Entry<Hash, EmptyKey> for Version {
|
|||
fn sort_key(&self) -> &EmptyKey {
|
||||
&EmptyKey
|
||||
}
|
||||
}
|
||||
|
||||
impl CRDT for Version {
|
||||
fn merge(&mut self, other: &Self) {
|
||||
if other.deleted {
|
||||
self.deleted = true;
|
||||
self.deleted.merge(&other.deleted);
|
||||
|
||||
if self.deleted.get() {
|
||||
self.blocks.clear();
|
||||
} else if !self.deleted {
|
||||
for bi in other.blocks.iter() {
|
||||
match self
|
||||
.blocks
|
||||
.binary_search_by(|x| x.cmp_key().cmp(&bi.cmp_key()))
|
||||
{
|
||||
Ok(_) => (),
|
||||
Err(pos) => {
|
||||
self.blocks.insert(pos, bi.clone());
|
||||
}
|
||||
}
|
||||
}
|
||||
} else {
|
||||
self.blocks.merge(&other.blocks);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
@ -121,14 +104,15 @@ impl TableSchema for VersionTable {
|
|||
self.background.spawn(async move {
|
||||
if let (Some(old_v), Some(new_v)) = (old, new) {
|
||||
// Propagate deletion of version blocks
|
||||
if new_v.deleted && !old_v.deleted {
|
||||
if new_v.deleted.get() && !old_v.deleted.get() {
|
||||
let deleted_block_refs = old_v
|
||||
.blocks
|
||||
.items()
|
||||
.iter()
|
||||
.map(|vb| BlockRef {
|
||||
.map(|(_k, vb)| BlockRef {
|
||||
block: vb.hash,
|
||||
version: old_v.uuid,
|
||||
deleted: true,
|
||||
deleted: true.into(),
|
||||
})
|
||||
.collect::<Vec<_>>();
|
||||
block_ref_table.insert_many(&deleted_block_refs[..]).await?;
|
||||
|
@ -139,6 +123,6 @@ impl TableSchema for VersionTable {
|
|||
}
|
||||
|
||||
fn matches_filter(entry: &Self::E, filter: &Self::Filter) -> bool {
|
||||
filter.apply(entry.deleted)
|
||||
filter.apply(entry.deleted.get())
|
||||
}
|
||||
}
|
||||
|
|
|
@ -1,327 +0,0 @@
|
|||
//! This package provides a simple implementation of conflict-free replicated data types (CRDTs)
|
||||
//!
|
||||
//! CRDTs are a type of data structures that do not require coordination. In other words, we can
|
||||
//! edit them in parallel, we will always find a way to merge it.
|
||||
//!
|
||||
//! A general example is a counter. Its initial value is 0. Alice and Bob get a copy of the
|
||||
//! counter. Alice does +1 on her copy, she reads 1. Bob does +3 on his copy, he reads 3. Now,
|
||||
//! it is easy to merge their counters, order does not count: we always get 4.
|
||||
//!
|
||||
//! Learn more about CRDT [on Wikipedia](https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
|
||||
|
||||
use serde::{Deserialize, Serialize};
|
||||
|
||||
use garage_util::data::*;
|
||||
|
||||
/// Definition of a CRDT - all CRDT Rust types implement this.
|
||||
///
|
||||
/// A CRDT is defined as a merge operator that respects a certain set of axioms.
|
||||
///
|
||||
/// In particular, the merge operator must be commutative, associative,
|
||||
/// idempotent, and monotonic.
|
||||
/// In other words, if `a`, `b` and `c` are CRDTs, and `⊔` denotes the merge operator,
|
||||
/// the following axioms must apply:
|
||||
///
|
||||
/// ```text
|
||||
/// a ⊔ b = b ⊔ a (commutativity)
|
||||
/// (a ⊔ b) ⊔ c = a ⊔ (b ⊔ c) (associativity)
|
||||
/// (a ⊔ b) ⊔ b = a ⊔ b (idempotence)
|
||||
/// ```
|
||||
///
|
||||
/// Moreover, the relationship `≥` defined by `a ≥ b ⇔ ∃c. a = b ⊔ c` must be a partial order.
|
||||
/// This implies a few properties such as: if `a ⊔ b ≠ a`, then there is no `c` such that `(a ⊔ b) ⊔ c = a`,
|
||||
/// as this would imply a cycle in the partial order.
|
||||
pub trait CRDT {
|
||||
/// Merge the two datastructures according to the CRDT rules.
|
||||
/// `self` is modified to contain the merged CRDT value. `other` is not modified.
|
||||
///
|
||||
/// # Arguments
|
||||
///
|
||||
/// * `other` - the other CRDT we wish to merge with
|
||||
fn merge(&mut self, other: &Self);
|
||||
}
|
||||
|
||||
/// All types that implement `Ord` (a total order) also implement a trivial CRDT
|
||||
/// defined by the merge rule: `a ⊔ b = max(a, b)`.
|
||||
impl<T> CRDT for T
|
||||
where
|
||||
T: Ord + Clone,
|
||||
{
|
||||
fn merge(&mut self, other: &Self) {
|
||||
if other > self {
|
||||
*self = other.clone();
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// ---- LWW Register ----
|
||||
|
||||
/// Last Write Win (LWW)
|
||||
///
|
||||
/// An LWW CRDT associates a timestamp with a value, in order to implement a
|
||||
/// time-based reconciliation rule: the most recent write wins.
|
||||
/// For completeness, the LWW reconciliation rule must also be defined for two LWW CRDTs
|
||||
/// with the same timestamp but different values.
|
||||
///
|
||||
/// In our case, we add the constraint that the value that is wrapped inside the LWW CRDT must
|
||||
/// itself be a CRDT: in the case when the timestamp does not allow us to decide on which value to
|
||||
/// keep, the merge rule of the inner CRDT is applied on the wrapped values. (Note that all types
|
||||
/// that implement the `Ord` trait get a default CRDT implemetnation that keeps the maximum value.
|
||||
/// This enables us to use LWW directly with primitive data types such as numbers or strings. It is
|
||||
/// generally desirable in this case to never explicitly produce LWW values with the same timestamp
|
||||
/// but different inner values, as the rule to keep the maximum value isn't generally the desired
|
||||
/// semantics.)
|
||||
///
|
||||
/// As multiple computers clocks are always desynchronized,
|
||||
/// when operations are close enough, it is equivalent to
|
||||
/// take one copy and drop the other one.
|
||||
///
|
||||
/// Given that clocks are not too desynchronized, this assumption
|
||||
/// is enough for most cases, as there is few chance that two humans
|
||||
/// coordonate themself faster than the time difference between two NTP servers.
|
||||
///
|
||||
/// As a more concret example, let's suppose you want to upload a file
|
||||
/// with the same key (path) in the same bucket at the very same time.
|
||||
/// For each request, the file will be timestamped by the receiving server
|
||||
/// and may differ from what you observed with your atomic clock!
|
||||
///
|
||||
/// This scheme is used by AWS S3 or Soundcloud and often without knowing
|
||||
/// in entreprise when reconciliating databases with ad-hoc scripts.
|
||||
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
|
||||
pub struct LWW<T> {
|
||||
ts: u64,
|
||||
v: T,
|
||||
}
|
||||
|
||||
impl<T> LWW<T>
|
||||
where
|
||||
T: CRDT,
|
||||
{
|
||||
/// Creates a new CRDT
|
||||
///
|
||||
/// CRDT's internal timestamp is set with current node's clock.
|
||||
pub fn new(value: T) -> Self {
|
||||
Self {
|
||||
ts: now_msec(),
|
||||
v: value,
|
||||
}
|
||||
}
|
||||
|
||||
/// Build a new CRDT from a previous non-compatible one
|
||||
///
|
||||
/// Compared to new, the CRDT's timestamp is not set to now
|
||||
/// but must be set to the previous, non-compatible, CRDT's timestamp.
|
||||
pub fn migrate_from_raw(ts: u64, value: T) -> Self {
|
||||
Self { ts, v: value }
|
||||
}
|
||||
|
||||
/// Update the LWW CRDT while keeping some causal ordering.
|
||||
///
|
||||
/// The timestamp of the LWW CRDT is updated to be the current node's clock
|
||||
/// at time of update, or the previous timestamp + 1 if that's bigger,
|
||||
/// so that the new timestamp is always strictly larger than the previous one.
|
||||
/// This ensures that merging the update with the old value will result in keeping
|
||||
/// the updated value.
|
||||
pub fn update(&mut self, new_value: T) {
|
||||
self.ts = std::cmp::max(self.ts + 1, now_msec());
|
||||
self.v = new_value;
|
||||
}
|
||||
|
||||
/// Get the CRDT value
|
||||
pub fn get(&self) -> &T {
|
||||
&self.v
|
||||
}
|
||||
|
||||
/// Get a mutable reference to the CRDT's value
|
||||
///
|
||||
/// This is usefull to mutate the inside value without changing the LWW timestamp.
|
||||
/// When such mutation is done, the merge between two LWW values is done using the inner
|
||||
/// CRDT's merge operation. This is usefull in the case where the inner CRDT is a large
|
||||
/// data type, such as a map, and we only want to change a single item in the map.
|
||||
/// To do this, we can produce a "CRDT delta", i.e. a LWW that contains only the modification.
|
||||
/// This delta consists in a LWW with the same timestamp, and the map
|
||||
/// inside only contains the updated value.
|
||||
/// The advantage of such a delta is that it is much smaller than the whole map.
|
||||
///
|
||||
/// Avoid using this if the inner data type is a primitive type such as a number or a string,
|
||||
/// as you will then rely on the merge function defined on `Ord` types by keeping the maximum
|
||||
/// of both values.
|
||||
pub fn get_mut(&mut self) -> &mut T {
|
||||
&mut self.v
|
||||
}
|
||||
}
|
||||
|
||||
impl<T> CRDT for LWW<T>
|
||||
where
|
||||
T: Clone + CRDT,
|
||||
{
|
||||
fn merge(&mut self, other: &Self) {
|
||||
if other.ts > self.ts {
|
||||
self.ts = other.ts;
|
||||
self.v = other.v.clone();
|
||||
} else if other.ts == self.ts {
|
||||
self.v.merge(&other.v);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/// Boolean, where `true` is an absorbing state
|
||||
#[derive(Clone, Copy, Debug, Serialize, Deserialize, PartialEq)]
|
||||
pub struct Bool(bool);
|
||||
|
||||
impl Bool {
|
||||
/// Create a new boolean with the specified value
|
||||
pub fn new(b: bool) -> Self {
|
||||
Self(b)
|
||||
}
|
||||
/// Set the boolean to true
|
||||
pub fn set(&mut self) {
|
||||
self.0 = true;
|
||||
}
|
||||
/// Get the boolean value
|
||||
pub fn get(&self) -> bool {
|
||||
self.0
|
||||
}
|
||||
}
|
||||
|
||||
impl CRDT for Bool {
|
||||
fn merge(&mut self, other: &Self) {
|
||||
self.0 = self.0 || other.0;
|
||||
}
|
||||
}
|
||||
|
||||
/// Last Write Win Map
|
||||
///
|
||||
/// This types defines a CRDT for a map from keys to values.
|
||||
/// The values have an associated timestamp, such that the last written value
|
||||
/// takes precedence over previous ones. As for the simpler `LWW` type, the value
|
||||
/// type `V` is also required to implement the CRDT trait.
|
||||
/// We do not encourage mutating the values associated with a given key
|
||||
/// without updating the timestamp, in fact at the moment we do not provide a `.get_mut()`
|
||||
/// method that would allow that.
|
||||
///
|
||||
/// Internally, the map is stored as a vector of keys and values, sorted by ascending key order.
|
||||
/// This is why the key type `K` must implement `Ord` (and also to ensure a unique serialization,
|
||||
/// such that two values can be compared for equality based on their hashes). As a consequence,
|
||||
/// insertions take `O(n)` time. This means that LWWMap should be used for reasonably small maps.
|
||||
/// However, note that even if we were using a more efficient data structure such as a `BTreeMap`,
|
||||
/// the serialization cost `O(n)` would still have to be paid at each modification, so we are
|
||||
/// actually not losing anything here.
|
||||
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
|
||||
pub struct LWWMap<K, V> {
|
||||
vals: Vec<(K, u64, V)>,
|
||||
}
|
||||
|
||||
impl<K, V> LWWMap<K, V>
|
||||
where
|
||||
K: Ord,
|
||||
V: CRDT,
|
||||
{
|
||||
/// Create a new empty map CRDT
|
||||
pub fn new() -> Self {
|
||||
Self { vals: vec![] }
|
||||
}
|
||||
/// Used to migrate from a map defined in an incompatible format. This produces
|
||||
/// a map that contains a single item with the specified timestamp (copied from
|
||||
/// the incompatible format). Do this as many times as you have items to migrate,
|
||||
/// and put them all together using the CRDT merge operator.
|
||||
pub fn migrate_from_raw_item(k: K, ts: u64, v: V) -> Self {
|
||||
Self {
|
||||
vals: vec![(k, ts, v)],
|
||||
}
|
||||
}
|
||||
/// Returns a map that contains a single mapping from the specified key to the specified value.
|
||||
/// This map is a mutator, or a delta-CRDT, such that when it is merged with the original map,
|
||||
/// the previous value will be replaced with the one specified here.
|
||||
/// The timestamp in the provided mutator is set to the maximum of the current system's clock
|
||||
/// and 1 + the previous value's timestamp (if there is one), so that the new value will always
|
||||
/// take precedence (LWW rule).
|
||||
///
|
||||
/// Typically, to update the value associated to a key in the map, you would do the following:
|
||||
///
|
||||
/// ```ignore
|
||||
/// let my_update = my_crdt.update_mutator(key_to_modify, new_value);
|
||||
/// my_crdt.merge(&my_update);
|
||||
/// ```
|
||||
///
|
||||
/// However extracting the mutator on its own and only sending that on the network is very
|
||||
/// interesting as it is much smaller than the whole map.
|
||||
pub fn update_mutator(&self, k: K, new_v: V) -> Self {
|
||||
let new_vals = match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
|
||||
Ok(i) => {
|
||||
let (_, old_ts, _) = self.vals[i];
|
||||
let new_ts = std::cmp::max(old_ts + 1, now_msec());
|
||||
vec![(k, new_ts, new_v)]
|
||||
}
|
||||
Err(_) => vec![(k, now_msec(), new_v)],
|
||||
};
|
||||
Self { vals: new_vals }
|
||||
}
|
||||
/// Takes all of the values of the map and returns them. The current map is reset to the
|
||||
/// empty map. This is very usefull to produce in-place a new map that contains only a delta
|
||||
/// that modifies a certain value:
|
||||
///
|
||||
/// ```ignore
|
||||
/// let mut a = get_my_crdt_value();
|
||||
/// let old_a = a.take_and_clear();
|
||||
/// a.merge(&old_a.update_mutator(key_to_modify, new_value));
|
||||
/// put_my_crdt_value(a);
|
||||
/// ```
|
||||
///
|
||||
/// Of course in this simple example we could have written simply
|
||||
/// `pyt_my_crdt_value(a.update_mutator(key_to_modify, new_value))`,
|
||||
/// but in the case where the map is a field in a struct for instance (as is always the case),
|
||||
/// this becomes very handy:
|
||||
///
|
||||
/// ```ignore
|
||||
/// let mut a = get_my_crdt_value();
|
||||
/// let old_a_map = a.map_field.take_and_clear();
|
||||
/// a.map_field.merge(&old_a_map.update_mutator(key_to_modify, new_value));
|
||||
/// put_my_crdt_value(a);
|
||||
/// ```
|
||||
pub fn take_and_clear(&mut self) -> Self {
|
||||
let vals = std::mem::replace(&mut self.vals, vec![]);
|
||||
Self { vals }
|
||||
}
|
||||
/// Removes all values from the map
|
||||
pub fn clear(&mut self) {
|
||||
self.vals.clear();
|
||||
}
|
||||
/// Get a reference to the value assigned to a key
|
||||
pub fn get(&self, k: &K) -> Option<&V> {
|
||||
match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
|
||||
Ok(i) => Some(&self.vals[i].2),
|
||||
Err(_) => None,
|
||||
}
|
||||
}
|
||||
/// Gets a reference to all of the items, as a slice. Usefull to iterate on all map values.
|
||||
/// In most case you will want to ignore the timestamp (second item of the tuple).
|
||||
pub fn items(&self) -> &[(K, u64, V)] {
|
||||
&self.vals[..]
|
||||
}
|
||||
}
|
||||
|
||||
impl<K, V> CRDT for LWWMap<K, V>
|
||||
where
|
||||
K: Clone + Ord,
|
||||
V: Clone + CRDT,
|
||||
{
|
||||
fn merge(&mut self, other: &Self) {
|
||||
for (k, ts2, v2) in other.vals.iter() {
|
||||
match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
|
||||
Ok(i) => {
|
||||
let (_, ts1, _v1) = &self.vals[i];
|
||||
if ts2 > ts1 {
|
||||
self.vals[i].1 = *ts2;
|
||||
self.vals[i].2 = v2.clone();
|
||||
} else if ts1 == ts2 {
|
||||
self.vals[i].2.merge(&v2);
|
||||
}
|
||||
}
|
||||
Err(i) => {
|
||||
self.vals.insert(i, (k.clone(), *ts2, v2.clone()));
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
34
src/table/crdt/bool.rs
Normal file
34
src/table/crdt/bool.rs
Normal file
|
@ -0,0 +1,34 @@
|
|||
use serde::{Deserialize, Serialize};
|
||||
|
||||
use crate::crdt::crdt::*;
|
||||
|
||||
/// Boolean, where `true` is an absorbing state
|
||||
#[derive(Clone, Copy, Debug, Serialize, Deserialize, PartialEq)]
|
||||
pub struct Bool(bool);
|
||||
|
||||
impl Bool {
|
||||
/// Create a new boolean with the specified value
|
||||
pub fn new(b: bool) -> Self {
|
||||
Self(b)
|
||||
}
|
||||
/// Set the boolean to true
|
||||
pub fn set(&mut self) {
|
||||
self.0 = true;
|
||||
}
|
||||
/// Get the boolean value
|
||||
pub fn get(&self) -> bool {
|
||||
self.0
|
||||
}
|
||||
}
|
||||
|
||||
impl From<bool> for Bool {
|
||||
fn from(b: bool) -> Bool {
|
||||
Bool::new(b)
|
||||
}
|
||||
}
|
||||
|
||||
impl CRDT for Bool {
|
||||
fn merge(&mut self, other: &Self) {
|
||||
self.0 = self.0 || other.0;
|
||||
}
|
||||
}
|
73
src/table/crdt/crdt.rs
Normal file
73
src/table/crdt/crdt.rs
Normal file
|
@ -0,0 +1,73 @@
|
|||
use garage_util::data::*;
|
||||
|
||||
/// Definition of a CRDT - all CRDT Rust types implement this.
|
||||
///
|
||||
/// A CRDT is defined as a merge operator that respects a certain set of axioms.
|
||||
///
|
||||
/// In particular, the merge operator must be commutative, associative,
|
||||
/// idempotent, and monotonic.
|
||||
/// In other words, if `a`, `b` and `c` are CRDTs, and `⊔` denotes the merge operator,
|
||||
/// the following axioms must apply:
|
||||
///
|
||||
/// ```text
|
||||
/// a ⊔ b = b ⊔ a (commutativity)
|
||||
/// (a ⊔ b) ⊔ c = a ⊔ (b ⊔ c) (associativity)
|
||||
/// (a ⊔ b) ⊔ b = a ⊔ b (idempotence)
|
||||
/// ```
|
||||
///
|
||||
/// Moreover, the relationship `≥` defined by `a ≥ b ⇔ ∃c. a = b ⊔ c` must be a partial order.
|
||||
/// This implies a few properties such as: if `a ⊔ b ≠ a`, then there is no `c` such that `(a ⊔ b) ⊔ c = a`,
|
||||
/// as this would imply a cycle in the partial order.
|
||||
pub trait CRDT {
|
||||
/// Merge the two datastructures according to the CRDT rules.
|
||||
/// `self` is modified to contain the merged CRDT value. `other` is not modified.
|
||||
///
|
||||
/// # Arguments
|
||||
///
|
||||
/// * `other` - the other CRDT we wish to merge with
|
||||
fn merge(&mut self, other: &Self);
|
||||
}
|
||||
|
||||
/// All types that implement `Ord` (a total order) can also implement a trivial CRDT
|
||||
/// defined by the merge rule: `a ⊔ b = max(a, b)`. Implement this trait for your type
|
||||
/// to enable this behavior.
|
||||
pub trait AutoCRDT: Ord + Clone + std::fmt::Debug {
|
||||
/// WARN_IF_DIFFERENT: emit a warning when values differ. Set this to true if
|
||||
/// different values in your application should never happen. Set this to false
|
||||
/// if you are actually relying on the semantics of `a ⊔ b = max(a, b)`.
|
||||
const WARN_IF_DIFFERENT: bool;
|
||||
}
|
||||
|
||||
impl<T> CRDT for T
|
||||
where
|
||||
T: AutoCRDT,
|
||||
{
|
||||
fn merge(&mut self, other: &Self) {
|
||||
if Self::WARN_IF_DIFFERENT && self != other {
|
||||
warn!(
|
||||
"Different CRDT values should be the same (logic error!): {:?} vs {:?}",
|
||||
self, other
|
||||
);
|
||||
if other > self {
|
||||
*self = other.clone();
|
||||
}
|
||||
warn!("Making an arbitrary choice: {:?}", self);
|
||||
} else {
|
||||
if other > self {
|
||||
*self = other.clone();
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
impl AutoCRDT for String {
|
||||
const WARN_IF_DIFFERENT: bool = true;
|
||||
}
|
||||
|
||||
impl AutoCRDT for bool {
|
||||
const WARN_IF_DIFFERENT: bool = true;
|
||||
}
|
||||
|
||||
impl AutoCRDT for FixedBytes32 {
|
||||
const WARN_IF_DIFFERENT: bool = true;
|
||||
}
|
114
src/table/crdt/lww.rs
Normal file
114
src/table/crdt/lww.rs
Normal file
|
@ -0,0 +1,114 @@
|
|||
use serde::{Deserialize, Serialize};
|
||||
|
||||
use garage_util::data::now_msec;
|
||||
|
||||
use crate::crdt::crdt::*;
|
||||
|
||||
/// Last Write Win (LWW)
|
||||
///
|
||||
/// An LWW CRDT associates a timestamp with a value, in order to implement a
|
||||
/// time-based reconciliation rule: the most recent write wins.
|
||||
/// For completeness, the LWW reconciliation rule must also be defined for two LWW CRDTs
|
||||
/// with the same timestamp but different values.
|
||||
///
|
||||
/// In our case, we add the constraint that the value that is wrapped inside the LWW CRDT must
|
||||
/// itself be a CRDT: in the case when the timestamp does not allow us to decide on which value to
|
||||
/// keep, the merge rule of the inner CRDT is applied on the wrapped values. (Note that all types
|
||||
/// that implement the `Ord` trait get a default CRDT implemetnation that keeps the maximum value.
|
||||
/// This enables us to use LWW directly with primitive data types such as numbers or strings. It is
|
||||
/// generally desirable in this case to never explicitly produce LWW values with the same timestamp
|
||||
/// but different inner values, as the rule to keep the maximum value isn't generally the desired
|
||||
/// semantics.)
|
||||
///
|
||||
/// As multiple computers clocks are always desynchronized,
|
||||
/// when operations are close enough, it is equivalent to
|
||||
/// take one copy and drop the other one.
|
||||
///
|
||||
/// Given that clocks are not too desynchronized, this assumption
|
||||
/// is enough for most cases, as there is few chance that two humans
|
||||
/// coordonate themself faster than the time difference between two NTP servers.
|
||||
///
|
||||
/// As a more concret example, let's suppose you want to upload a file
|
||||
/// with the same key (path) in the same bucket at the very same time.
|
||||
/// For each request, the file will be timestamped by the receiving server
|
||||
/// and may differ from what you observed with your atomic clock!
|
||||
///
|
||||
/// This scheme is used by AWS S3 or Soundcloud and often without knowing
|
||||
/// in entreprise when reconciliating databases with ad-hoc scripts.
|
||||
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
|
||||
pub struct LWW<T> {
|
||||
ts: u64,
|
||||
v: T,
|
||||
}
|
||||
|
||||
impl<T> LWW<T>
|
||||
where
|
||||
T: CRDT,
|
||||
{
|
||||
/// Creates a new CRDT
|
||||
///
|
||||
/// CRDT's internal timestamp is set with current node's clock.
|
||||
pub fn new(value: T) -> Self {
|
||||
Self {
|
||||
ts: now_msec(),
|
||||
v: value,
|
||||
}
|
||||
}
|
||||
|
||||
/// Build a new CRDT from a previous non-compatible one
|
||||
///
|
||||
/// Compared to new, the CRDT's timestamp is not set to now
|
||||
/// but must be set to the previous, non-compatible, CRDT's timestamp.
|
||||
pub fn migrate_from_raw(ts: u64, value: T) -> Self {
|
||||
Self { ts, v: value }
|
||||
}
|
||||
|
||||
/// Update the LWW CRDT while keeping some causal ordering.
|
||||
///
|
||||
/// The timestamp of the LWW CRDT is updated to be the current node's clock
|
||||
/// at time of update, or the previous timestamp + 1 if that's bigger,
|
||||
/// so that the new timestamp is always strictly larger than the previous one.
|
||||
/// This ensures that merging the update with the old value will result in keeping
|
||||
/// the updated value.
|
||||
pub fn update(&mut self, new_value: T) {
|
||||
self.ts = std::cmp::max(self.ts + 1, now_msec());
|
||||
self.v = new_value;
|
||||
}
|
||||
|
||||
/// Get the CRDT value
|
||||
pub fn get(&self) -> &T {
|
||||
&self.v
|
||||
}
|
||||
|
||||
/// Get a mutable reference to the CRDT's value
|
||||
///
|
||||
/// This is usefull to mutate the inside value without changing the LWW timestamp.
|
||||
/// When such mutation is done, the merge between two LWW values is done using the inner
|
||||
/// CRDT's merge operation. This is usefull in the case where the inner CRDT is a large
|
||||
/// data type, such as a map, and we only want to change a single item in the map.
|
||||
/// To do this, we can produce a "CRDT delta", i.e. a LWW that contains only the modification.
|
||||
/// This delta consists in a LWW with the same timestamp, and the map
|
||||
/// inside only contains the updated value.
|
||||
/// The advantage of such a delta is that it is much smaller than the whole map.
|
||||
///
|
||||
/// Avoid using this if the inner data type is a primitive type such as a number or a string,
|
||||
/// as you will then rely on the merge function defined on `Ord` types by keeping the maximum
|
||||
/// of both values.
|
||||
pub fn get_mut(&mut self) -> &mut T {
|
||||
&mut self.v
|
||||
}
|
||||
}
|
||||
|
||||
impl<T> CRDT for LWW<T>
|
||||
where
|
||||
T: Clone + CRDT,
|
||||
{
|
||||
fn merge(&mut self, other: &Self) {
|
||||
if other.ts > self.ts {
|
||||
self.ts = other.ts;
|
||||
self.v = other.v.clone();
|
||||
} else if other.ts == self.ts {
|
||||
self.v.merge(&other.v);
|
||||
}
|
||||
}
|
||||
}
|
145
src/table/crdt/lww_map.rs
Normal file
145
src/table/crdt/lww_map.rs
Normal file
|
@ -0,0 +1,145 @@
|
|||
use serde::{Deserialize, Serialize};
|
||||
|
||||
use garage_util::data::now_msec;
|
||||
|
||||
use crate::crdt::crdt::*;
|
||||
|
||||
/// Last Write Win Map
|
||||
///
|
||||
/// This types defines a CRDT for a map from keys to values.
|
||||
/// The values have an associated timestamp, such that the last written value
|
||||
/// takes precedence over previous ones. As for the simpler `LWW` type, the value
|
||||
/// type `V` is also required to implement the CRDT trait.
|
||||
/// We do not encourage mutating the values associated with a given key
|
||||
/// without updating the timestamp, in fact at the moment we do not provide a `.get_mut()`
|
||||
/// method that would allow that.
|
||||
///
|
||||
/// Internally, the map is stored as a vector of keys and values, sorted by ascending key order.
|
||||
/// This is why the key type `K` must implement `Ord` (and also to ensure a unique serialization,
|
||||
/// such that two values can be compared for equality based on their hashes). As a consequence,
|
||||
/// insertions take `O(n)` time. This means that LWWMap should be used for reasonably small maps.
|
||||
/// However, note that even if we were using a more efficient data structure such as a `BTreeMap`,
|
||||
/// the serialization cost `O(n)` would still have to be paid at each modification, so we are
|
||||
/// actually not losing anything here.
|
||||
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
|
||||
pub struct LWWMap<K, V> {
|
||||
vals: Vec<(K, u64, V)>,
|
||||
}
|
||||
|
||||
impl<K, V> LWWMap<K, V>
|
||||
where
|
||||
K: Ord,
|
||||
V: CRDT,
|
||||
{
|
||||
/// Create a new empty map CRDT
|
||||
pub fn new() -> Self {
|
||||
Self { vals: vec![] }
|
||||
}
|
||||
/// Used to migrate from a map defined in an incompatible format. This produces
|
||||
/// a map that contains a single item with the specified timestamp (copied from
|
||||
/// the incompatible format). Do this as many times as you have items to migrate,
|
||||
/// and put them all together using the CRDT merge operator.
|
||||
pub fn migrate_from_raw_item(k: K, ts: u64, v: V) -> Self {
|
||||
Self {
|
||||
vals: vec![(k, ts, v)],
|
||||
}
|
||||
}
|
||||
/// Returns a map that contains a single mapping from the specified key to the specified value.
|
||||
/// This map is a mutator, or a delta-CRDT, such that when it is merged with the original map,
|
||||
/// the previous value will be replaced with the one specified here.
|
||||
/// The timestamp in the provided mutator is set to the maximum of the current system's clock
|
||||
/// and 1 + the previous value's timestamp (if there is one), so that the new value will always
|
||||
/// take precedence (LWW rule).
|
||||
///
|
||||
/// Typically, to update the value associated to a key in the map, you would do the following:
|
||||
///
|
||||
/// ```ignore
|
||||
/// let my_update = my_crdt.update_mutator(key_to_modify, new_value);
|
||||
/// my_crdt.merge(&my_update);
|
||||
/// ```
|
||||
///
|
||||
/// However extracting the mutator on its own and only sending that on the network is very
|
||||
/// interesting as it is much smaller than the whole map.
|
||||
pub fn update_mutator(&self, k: K, new_v: V) -> Self {
|
||||
let new_vals = match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
|
||||
Ok(i) => {
|
||||
let (_, old_ts, _) = self.vals[i];
|
||||
let new_ts = std::cmp::max(old_ts + 1, now_msec());
|
||||
vec![(k, new_ts, new_v)]
|
||||
}
|
||||
Err(_) => vec![(k, now_msec(), new_v)],
|
||||
};
|
||||
Self { vals: new_vals }
|
||||
}
|
||||
/// Takes all of the values of the map and returns them. The current map is reset to the
|
||||
/// empty map. This is very usefull to produce in-place a new map that contains only a delta
|
||||
/// that modifies a certain value:
|
||||
///
|
||||
/// ```ignore
|
||||
/// let mut a = get_my_crdt_value();
|
||||
/// let old_a = a.take_and_clear();
|
||||
/// a.merge(&old_a.update_mutator(key_to_modify, new_value));
|
||||
/// put_my_crdt_value(a);
|
||||
/// ```
|
||||
///
|
||||
/// Of course in this simple example we could have written simply
|
||||
/// `pyt_my_crdt_value(a.update_mutator(key_to_modify, new_value))`,
|
||||
/// but in the case where the map is a field in a struct for instance (as is always the case),
|
||||
/// this becomes very handy:
|
||||
///
|
||||
/// ```ignore
|
||||
/// let mut a = get_my_crdt_value();
|
||||
/// let old_a_map = a.map_field.take_and_clear();
|
||||
/// a.map_field.merge(&old_a_map.update_mutator(key_to_modify, new_value));
|
||||
/// put_my_crdt_value(a);
|
||||
/// ```
|
||||
pub fn take_and_clear(&mut self) -> Self {
|
||||
let vals = std::mem::replace(&mut self.vals, vec![]);
|
||||
Self { vals }
|
||||
}
|
||||
/// Removes all values from the map
|
||||
pub fn clear(&mut self) {
|
||||
self.vals.clear();
|
||||
}
|
||||
/// Get a reference to the value assigned to a key
|
||||
pub fn get(&self, k: &K) -> Option<&V> {
|
||||
match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
|
||||
Ok(i) => Some(&self.vals[i].2),
|
||||
Err(_) => None,
|
||||
}
|
||||
}
|
||||
/// Gets a reference to all of the items, as a slice. Usefull to iterate on all map values.
|
||||
/// In most case you will want to ignore the timestamp (second item of the tuple).
|
||||
pub fn items(&self) -> &[(K, u64, V)] {
|
||||
&self.vals[..]
|
||||
}
|
||||
/// Returns the number of items in the map
|
||||
pub fn len(&self) -> usize {
|
||||
self.vals.len()
|
||||
}
|
||||
}
|
||||
|
||||
impl<K, V> CRDT for LWWMap<K, V>
|
||||
where
|
||||
K: Clone + Ord,
|
||||
V: Clone + CRDT,
|
||||
{
|
||||
fn merge(&mut self, other: &Self) {
|
||||
for (k, ts2, v2) in other.vals.iter() {
|
||||
match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
|
||||
Ok(i) => {
|
||||
let (_, ts1, _v1) = &self.vals[i];
|
||||
if ts2 > ts1 {
|
||||
self.vals[i].1 = *ts2;
|
||||
self.vals[i].2 = v2.clone();
|
||||
} else if ts1 == ts2 {
|
||||
self.vals[i].2.merge(&v2);
|
||||
}
|
||||
}
|
||||
Err(i) => {
|
||||
self.vals.insert(i, (k.clone(), *ts2, v2.clone()));
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
83
src/table/crdt/map.rs
Normal file
83
src/table/crdt/map.rs
Normal file
|
@ -0,0 +1,83 @@
|
|||
use serde::{Deserialize, Serialize};
|
||||
|
||||
use crate::crdt::crdt::*;
|
||||
|
||||
/// Simple CRDT Map
|
||||
///
|
||||
/// This types defines a CRDT for a map from keys to values. Values are CRDT types which
|
||||
/// can have their own updating logic.
|
||||
///
|
||||
/// Internally, the map is stored as a vector of keys and values, sorted by ascending key order.
|
||||
/// This is why the key type `K` must implement `Ord` (and also to ensure a unique serialization,
|
||||
/// such that two values can be compared for equality based on their hashes). As a consequence,
|
||||
/// insertions take `O(n)` time. This means that Map should be used for reasonably small maps.
|
||||
/// However, note that even if we were using a more efficient data structure such as a `BTreeMap`,
|
||||
/// the serialization cost `O(n)` would still have to be paid at each modification, so we are
|
||||
/// actually not losing anything here.
|
||||
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
|
||||
pub struct Map<K, V> {
|
||||
vals: Vec<(K, V)>,
|
||||
}
|
||||
|
||||
impl<K, V> Map<K, V>
|
||||
where
|
||||
K: Clone + Ord,
|
||||
V: Clone + CRDT,
|
||||
{
|
||||
/// Create a new empty map CRDT
|
||||
pub fn new() -> Self {
|
||||
Self { vals: vec![] }
|
||||
}
|
||||
|
||||
/// Returns a map that contains a single mapping from the specified key to the specified value.
|
||||
/// This can be used to build a delta-mutator:
|
||||
/// when merged with another map, the value will be added or CRDT-merged if a previous
|
||||
/// value already exists.
|
||||
pub fn put_mutator(k: K, v: V) -> Self {
|
||||
Self { vals: vec![(k, v)] }
|
||||
}
|
||||
|
||||
pub fn put(&mut self, k: K, v: V) {
|
||||
self.merge(&Self::put_mutator(k, v));
|
||||
}
|
||||
|
||||
/// Removes all values from the map
|
||||
pub fn clear(&mut self) {
|
||||
self.vals.clear();
|
||||
}
|
||||
|
||||
/// Get a reference to the value assigned to a key
|
||||
pub fn get(&self, k: &K) -> Option<&V> {
|
||||
match self.vals.binary_search_by(|(k2, _)| k2.cmp(&k)) {
|
||||
Ok(i) => Some(&self.vals[i].1),
|
||||
Err(_) => None,
|
||||
}
|
||||
}
|
||||
/// Gets a reference to all of the items, as a slice. Usefull to iterate on all map values.
|
||||
pub fn items(&self) -> &[(K, V)] {
|
||||
&self.vals[..]
|
||||
}
|
||||
/// Returns the number of items in the map
|
||||
pub fn len(&self) -> usize {
|
||||
self.vals.len()
|
||||
}
|
||||
}
|
||||
|
||||
impl<K, V> CRDT for Map<K, V>
|
||||
where
|
||||
K: Clone + Ord,
|
||||
V: Clone + CRDT,
|
||||
{
|
||||
fn merge(&mut self, other: &Self) {
|
||||
for (k, v2) in other.vals.iter() {
|
||||
match self.vals.binary_search_by(|(k2, _)| k2.cmp(&k)) {
|
||||
Ok(i) => {
|
||||
self.vals[i].1.merge(&v2);
|
||||
}
|
||||
Err(i) => {
|
||||
self.vals.insert(i, (k.clone(), v2.clone()));
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
22
src/table/crdt/mod.rs
Normal file
22
src/table/crdt/mod.rs
Normal file
|
@ -0,0 +1,22 @@
|
|||
//! This package provides a simple implementation of conflict-free replicated data types (CRDTs)
|
||||
//!
|
||||
//! CRDTs are a type of data structures that do not require coordination. In other words, we can
|
||||
//! edit them in parallel, we will always find a way to merge it.
|
||||
//!
|
||||
//! A general example is a counter. Its initial value is 0. Alice and Bob get a copy of the
|
||||
//! counter. Alice does +1 on her copy, she reads 1. Bob does +3 on his copy, he reads 3. Now,
|
||||
//! it is easy to merge their counters, order does not count: we always get 4.
|
||||
//!
|
||||
//! Learn more about CRDT [on Wikipedia](https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
|
||||
|
||||
mod bool;
|
||||
mod crdt;
|
||||
mod lww;
|
||||
mod lww_map;
|
||||
mod map;
|
||||
|
||||
pub use self::bool::*;
|
||||
pub use crdt::*;
|
||||
pub use lww::*;
|
||||
pub use lww_map::*;
|
||||
pub use map::*;
|
|
@ -2,6 +2,8 @@ use serde::{Deserialize, Serialize};
|
|||
|
||||
use garage_util::data::*;
|
||||
|
||||
use crate::crdt::CRDT;
|
||||
|
||||
pub trait PartitionKey {
|
||||
fn hash(&self) -> Hash;
|
||||
}
|
||||
|
@ -35,12 +37,10 @@ impl SortKey for Hash {
|
|||
}
|
||||
|
||||
pub trait Entry<P: PartitionKey, S: SortKey>:
|
||||
PartialEq + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync
|
||||
CRDT + PartialEq + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync
|
||||
{
|
||||
fn partition_key(&self) -> &P;
|
||||
fn sort_key(&self) -> &S;
|
||||
|
||||
fn merge(&mut self, other: &Self);
|
||||
}
|
||||
|
||||
pub trait TableSchema: Send + Sync {
|
||||
|
|
|
@ -17,6 +17,7 @@ use garage_rpc::ring::Ring;
|
|||
use garage_rpc::rpc_client::*;
|
||||
use garage_rpc::rpc_server::*;
|
||||
|
||||
use crate::crdt::CRDT;
|
||||
use crate::schema::*;
|
||||
use crate::table_sync::*;
|
||||
|
||||
|
|
Loading…
Reference in a new issue