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Add term history to safekeepers.

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Persist full history of term switches on safekeepers instead of storing only the
single term of the highest entry (called epoch). This allows easily and
correctly find the divergence point of two logs and truncate the obsolete part
before overwriting it with entries of the newer proposer(s).

Full history of the proposer is transferred in separate message before proposer
starts streaming; it is immediately persisted by safekeeper, though he might not
yet have entries for some older terms there. That's because we can't atomically
append to WAL and update the control file anyway, so locally available WAL must
be taken into account when looking at the history.

We should sometimes purge term history entries beyond truncate_lsn; this is not
done here.

Per https://github.com/zenithdb/rfcs/pull/12

Closes #296.

Bumps vendor/postgres.
This commit is contained in:
Arseny Sher
2021-11-05 13:39:41 +03:00
parent 2669d140f8
commit cba4da3f4d
7 changed files with 417 additions and 121 deletions
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22
walkeeper/src/http/routes.rs
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@@ -7,7 +7,8 @@ use std::fmt::Display;
use std::sync::Arc;
use zenith_utils::lsn::Lsn;
use crate::safekeeper::AcceptorState;
use crate::safekeeper::Term;
use crate::safekeeper::TermHistory;
use crate::timeline::CreateControlFile;
use crate::timeline::GlobalTimelines;
use crate::SafeKeeperConf;
@@ -29,6 +30,7 @@ fn get_conf(request: &Request<Body>) -> &SafeKeeperConf {
.as_ref()
}
/// Serialize through Display trait.
fn display_serialize<S, F>(z: &F, s: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
@@ -37,6 +39,14 @@ where
s.serialize_str(&format!("{}", z))
}
/// Augment AcceptorState with epoch for convenience
#[derive(Debug, Serialize)]
struct AcceptorStateStatus {
term: Term,
epoch: Term,
term_history: TermHistory,
}
/// Info about timeline on safekeeper ready for reporting.
#[derive(Debug, Serialize)]
struct TimelineStatus {
@@ -44,7 +54,7 @@ struct TimelineStatus {
tenant_id: ZTenantId,
#[serde(serialize_with = "display_serialize")]
timeline_id: ZTimelineId,
acceptor_state: AcceptorState,
acceptor_state: AcceptorStateStatus,
#[serde(serialize_with = "display_serialize")]
commit_lsn: Lsn,
#[serde(serialize_with = "display_serialize")]
@@ -68,10 +78,16 @@ async fn timeline_status_handler(request: Request<Body>) -> Result<Response<Body
let sk_state = tli.get_info();
let flush_lsn = tli.get_end_of_wal();
let acc_state = AcceptorStateStatus {
term: sk_state.acceptor_state.term,
epoch: sk_state.acceptor_state.get_epoch(flush_lsn),
term_history: sk_state.acceptor_state.term_history,
};
let status = TimelineStatus {
tenant_id,
timeline_id,
acceptor_state: sk_state.acceptor_state,
acceptor_state: acc_state,
commit_lsn: sk_state.commit_lsn,
truncate_lsn: sk_state.truncate_lsn,
flush_lsn,