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trim down merge_local_remote_metadata()

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This commit is contained in:
Christian Schwarz
2023-02-01 18:40:08 +01:00
parent 5e270ec037
commit 11cc103d1d
1 changed files with 18 additions and 38 deletions
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56
pageserver/src/tenant.rs
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@@ -418,25 +418,18 @@ impl Drop for TimelineUninitMark {
}
}
// We should not blindly overwrite local metadata with remote one.
// For example, consider the following case:
// Image layer is flushed to disk as a new delta layer, we update local metadata and start upload task but after that
// pageserver crashes. During startup we'll load new metadata, and then reset it
// to the state of remote one. But current layermap will have layers from the old
// metadata which is inconsistent.
// And with current logic it wont disgard them during load because during layermap
// load it sees local disk consistent lsn which is ahead of layer lsns.
// If we treat remote as source of truth we need to completely sync with it,
// i e delete local files which are missing on the remote. This will add extra work,
// wal for these layers needs to be reingested for example
//
// So the solution is to take remote metadata only when we're attaching.
pub fn merge_local_remote_metadata<'a>(
/// Verify that the local state is en-par or ahead of the remote state.
/// If this function returns an error, it is likely that some other pageserver
/// wrote to the remote, so, we better bail out to avoid the risk of split-brain.
///
/// If `remote` is None, it is assumed that there is not remote state, so, the
/// function returns `Ok()` in that case.
fn verify_local_metadata_is_not_behind_remote<'a>(
local: &'a TimelineMetadata,
remote: Option<&'a TimelineMetadata>,
) -> anyhow::Result<(&'a TimelineMetadata, bool)> {
) -> anyhow::Result<()> {
match (local, remote) {
(local, None) => Ok((local, true)),
(_local, None) => Ok(()),
// This is the regular case where we crash/exit before finishing queued uploads.
(local, Some(remote)) => {
let consistent_lsn_cmp = local
@@ -448,13 +441,13 @@ pub fn merge_local_remote_metadata<'a>(
use std::cmp::Ordering::*;
match (consistent_lsn_cmp, gc_cutoff_lsn_cmp) {
// It wouldn't matter, but pick the local one so that we don't rewrite the metadata file.
(Equal, Equal) => Ok((local, true)),
(Equal, Equal) => Ok(()),
// Local state is clearly ahead of the remote.
(Greater, Greater) => Ok((local, true)),
(Greater, Greater) => Ok(()),
// We have local layer files that aren't on the remote, but GC horizon is on par.
(Greater, Equal) => Ok((local, true)),
(Greater, Equal) => Ok(()),
// Local GC started running but we couldn't sync it to the remote.
(Equal, Greater) => Ok((local, true)),
(Equal, Greater) => Ok(()),
// We always update the local value first, so something else must have
// updated the remote value, probably a different pageserver.
@@ -506,12 +499,11 @@ impl Tenant {
) -> anyhow::Result<()> {
let tenant_id = self.tenant_id;
let (up_to_date_metadata, picked_local) = merge_local_remote_metadata(
verify_local_metadata_is_not_behind_remote(
&local_metadata,
remote_startup_data.as_ref().map(|r| &r.remote_metadata),
)
.context("merge_local_remote_metadata")?
.to_owned();
.context("merge_local_remote_metadata")?;
let timeline = {
// avoiding holding it across awaits
@@ -524,7 +516,7 @@ impl Tenant {
let dummy_timeline = self.create_timeline_data(
timeline_id,
up_to_date_metadata.clone(),
local_metadata.clone(),
ancestor.clone(),
remote_client,
)?;
@@ -549,7 +541,7 @@ impl Tenant {
let broken_timeline = self
.create_timeline_data(
timeline_id,
up_to_date_metadata.clone(),
local_metadata.clone(),
ancestor.clone(),
None,
)
@@ -569,7 +561,7 @@ impl Tenant {
// in remote storage.
timeline
.reconcile_with_remote(
up_to_date_metadata,
&local_metadata,
remote_startup_data.as_ref().map(|r| &r.index_part),
)
.await
@@ -589,18 +581,6 @@ impl Tenant {
"Timeline has no ancestor and no layer files"
);
// Save the metadata file to local disk.
if !picked_local {
save_metadata(
self.conf,
timeline_id,
tenant_id,
up_to_date_metadata,
false,
)
.context("save_metadata")?;
}
Ok(())
}