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Add more info about borrowed from Postgres structures (RelTag and BufferTag)

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Alexey Kondratov
2021-05-24 20:10:47 +03:00
committed by Alexey Kondratov
parent 263acef1cc
commit b1a424dfa9
1 changed files with 26 additions and 0 deletions
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26
pageserver/src/repository.rs
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@@ -177,6 +177,25 @@ pub struct RepositoryStats {
pub num_getpage_requests: Lsn,
}
///
/// Relation data file segment id throughout the Postgres cluster.
///
/// Every data file in Postgres is uniquely identified by 4 numbers:
/// - relation id / node (`relnode`)
/// - database id (`dbnode`)
/// - tablespace id (`spcnode`), in short this is a unique id of a separate
/// directory to store data files.
/// - forknumber (`forknum`) is used to split different kinds of data of the same relation
/// between some set of files (`relnode`, `relnode_fsm`, `relnode_vm`).
///
/// In native Postgres code `RelFileNode` structure and individual `ForkNumber` value
/// are used for the same purpose.
/// [See more related comments here](https:///github.com/postgres/postgres/blob/99c5852e20a0987eca1c38ba0c09329d4076b6a0/src/include/storage/relfilenode.h#L57).
///
/// We use additional fork numbers to logically separate relational and
/// non-relational data inside pageserver key-value storage.
/// See, e.g., `ROCKSDB_SPECIAL_FORKNUM`.
///
#[derive(Debug, PartialEq, Eq, PartialOrd, Hash, Ord, Clone, Copy, Serialize, Deserialize)]
pub struct RelTag {
pub forknum: u8,
@@ -203,6 +222,13 @@ impl fmt::Display for RelTag {
}
}
///
/// `RelTag` + block number (`blknum`) gives us a unique id of the page in the cluster.
/// This is used as a part of the key inside key-value storage (RocksDB currently).
///
/// In Postgres `BufferTag` structure is used for exactly the same purpose.
/// [See more related comments here](https://github.com/postgres/postgres/blob/99c5852e20a0987eca1c38ba0c09329d4076b6a0/src/include/storage/buf_internals.h#L91).
///
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Serialize, Deserialize)]
pub struct BufferTag {
pub rel: RelTag,