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Fix checking distance of last snapshot #77

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merged 1 commit into from
Oct 7, 2024
Merged

Fix checking distance of last snapshot #77

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29 changes: 22 additions & 7 deletions src/handle_commit.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -534,12 +534,28 @@ bool raft_server::snapshot_and_compact(ulong committed_idx, bool forced_creation
return false;
}

if ( ( forced_creation ||
snp_creation_scheduled_ ||
!local_snp ||
committed_idx >= snapshot_distance + local_snp->get_last_log_idx() ) &&
snp_in_progress_.compare_exchange_strong(f, true) )
{
auto can_create_snapshot = [&](const ptr<snapshot>& local_snapshot) {
if (forced_creation || snp_creation_scheduled_)
return true;

return !local_snapshot || committed_idx >= snapshot_distance + local_snapshot->get_last_log_idx();
};

if ( can_create_snapshot(local_snp) &&
snp_in_progress_.compare_exchange_strong(f, true) ) {
local_snp = get_last_snapshot();

// NOTE:
// Because we fetch local_snp before checking the flag snp_in_progress_
// we can have a newer snapshot that was created between
// fetching of local_snp and setting the snp_in_progress_ to false
// to avoid creating snapshots too soon, we recheck the distance when we are
// sure this is the only thread creating snapshot
if (!can_create_snapshot(local_snp)) {
snp_in_progress_ = false;
return false;
}

snapshot_in_action = true;
p_in("creating a snapshot for index %" PRIu64 "", committed_idx);

Expand All @@ -550,7 +566,6 @@ bool raft_server::snapshot_and_compact(ulong committed_idx, bool forced_creation
//
// To avoid such a case, while `snp_in_progress_` is true,
// we re-check the latest snapshot index here.
local_snp = get_last_snapshot();
if (local_snp && local_snp->get_last_log_idx() >= committed_idx) {
p_wn("snapshot index inversion detected, "
"skip snapshot creation for index %" PRIu64 ", "
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