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storage_service: Hoist migration precondition

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`prepare_for_tablets_migration()` is idempotent; it filters out tables
that already have tablet maps and returns early if no tablet maps need
to be created. However, this precondition is currently misplaced. Move
it higher to skip extra work.

Signed-off-by: Nikos Dragazis <nikolaos.dragazis@scylladb.com>
This commit is contained in:
Nikos Dragazis
2026-03-29 17:10:45 +03:00
parent f0e9177130
commit 8ea8c05120
1 changed files with 39 additions and 39 deletions
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78
service/storage_service.cc
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@@ -3928,45 +3928,6 @@ future<> storage_service::prepare_for_tablets_migration(const sstring& ks_name)
}
}
// Stateful lambdas for round-robin shard assignment per node.
std::unordered_map<locator::host_id, std::function<shard_id()>> next_shard_for;
tm.for_each_token_owner([&] (const locator::node& node) {
auto host = node.host_id();
next_shard_for[host] = [num_shards = node.get_shard_count(), idx = 0u]() mutable {
return shard_id(idx++ % num_shards);
};
});
slogger.info("Building tablet maps for tables in keyspace {} with {} tablet(s)", ks_name, tablet_count);
// Build a tablet_map from vnode token boundaries.
//
// The map contains one tablet per vnode. The replicas of each tablet are
// the same as the replicas of the corresponding vnode. Shards are assigned
// in round-robin fashion per node so that tablets are evenly distributed
// within each node.
// (FIXME: we should consider tablet sizes as well)
//
// This map will serve as a template for per-table tablet map mutations.
// Each table in the keyspace receives its own tablet map, but all maps
// have identical tablet boundaries and replica placement.
auto erm = ks.get_static_effective_replication_map();
locator::tablet_map tmap(tablet_count);
for (size_t i = 0; i < tablet_count; ++i) {
auto tablet = locator::tablet_id(i);
auto vnode_replica_hosts = erm->get_natural_replicas(sorted_tokens[i], true);
locator::tablet_replica_set tablet_replicas;
for (auto host : vnode_replica_hosts) {
tablet_replicas.push_back(locator::tablet_replica{host, next_shard_for[host]()});
}
tmap.set_tablet(tablet, locator::tablet_info(std::move(tablet_replicas)));
if (tmap.get_last_token(tablet) != sorted_tokens[i]) {
throw std::runtime_error(fmt::format("vnode token {} is not aligned; cannot be used as tablet boundary (expected: {})", sorted_tokens[i], tmap.get_last_token(tablet)));
}
}
std::vector<std::pair<table_id, sstring>> tables_to_migrate;
for (const auto& [name, schema] : cf_meta_data) {
@@ -3985,6 +3946,45 @@ future<> storage_service::prepare_for_tablets_migration(const sstring& ks_name)
co_return;
}
// Build a tablet_map from vnode token boundaries.
//
// The map contains one tablet per vnode. The replicas of each tablet are
// the same as the replicas of the corresponding vnode. Shards are assigned
// in round-robin fashion per node so that tablets are evenly distributed
// within each node.
// (FIXME: we should consider tablet sizes as well)
//
// This map will serve as a template for per-table tablet map mutations.
// Each table in the keyspace receives its own tablet map, but all maps
// have identical tablet boundaries and replica placement.
slogger.info("Building tablet maps for tables in keyspace {} with {} tablet(s)", ks_name, tablet_count);
// Stateful lambdas for round-robin shard assignment per node.
std::unordered_map<locator::host_id, std::function<shard_id()>> next_shard_for;
tm.for_each_token_owner([&] (const locator::node& node) {
auto host = node.host_id();
next_shard_for[host] = [num_shards = node.get_shard_count(), idx = 0u]() mutable {
return shard_id(idx++ % num_shards);
};
});
auto erm = ks.get_static_effective_replication_map();
locator::tablet_map tmap(tablet_count);
for (size_t i = 0; i < tablet_count; ++i) {
auto tablet = locator::tablet_id(i);
auto vnode_replica_hosts = erm->get_natural_replicas(sorted_tokens[i], true);
locator::tablet_replica_set tablet_replicas;
for (auto host : vnode_replica_hosts) {
tablet_replicas.push_back(locator::tablet_replica{host, next_shard_for[host]()});
}
tmap.set_tablet(tablet, locator::tablet_info(std::move(tablet_replicas)));
if (tmap.get_last_token(tablet) != sorted_tokens[i]) {
throw std::runtime_error(fmt::format("vnode token {} is not aligned; cannot be used as tablet boundary (expected: {})", sorted_tokens[i], tmap.get_last_token(tablet)));
}
}
// Build tablet map mutations for all tables and persist them to group0 (system.tablets)
// in a single command.
//