mito: Potential issue to recover truncated data about greptimedb

[evenyag]

Now the region doesn't consider truncated entries during replay.

greptimedb/src/mito2/src/region/opener.rs

Lines 256 to 270 in c2db970

	let flushed_entry_id = version.flushed_entry_id;
	let version_control = Arc::new(VersionControl::new(version));
	if !self.skip_wal_replay {
	info!(
	"Start replaying memtable at flushed_entry_id + 1 {} for region {}",
	flushed_entry_id + 1,
	region_id
	);
	replay_memtable(
	wal,
	&wal_options,
	region_id,
	flushed_entry_id,
	&version_control,
	)

It should skip entries <= truncated_entry_id. We might do this in replay_memtable().

[evenyag]

After checking how we recover the truncate action, I found that apply_truncate() updates the flushed entry id by the truncated entry id. Thus the region won't replay entries before the truncated entry id.

greptimedb/src/mito2/src/manifest/action.rs

Lines 147 to 153 in c2db970

	pub fn apply_truncate(&mut self, manifest_version: ManifestVersion, truncate: RegionTruncate) {
	self.manifest_version = manifest_version;
	self.flushed_entry_id = truncate.truncated_entry_id;
	self.flushed_sequence = truncate.truncated_sequence;
	self.truncated_entry_id = Some(truncate.truncated_entry_id);
	self.files.clear();
	}